diff mbox series

[v2,1/3] hw/net: Add npcm7xx emc model

Message ID 20210202232838.1641382-2-dje@google.com (mailing list archive)
State New, archived
Headers show
Series Add npcm7xx emc model | expand

Commit Message

Zhijian Li (Fujitsu)" via Feb. 2, 2021, 11:28 p.m. UTC
This is a 10/100 ethernet device that has several features.
Only the ones needed by the Linux driver have been implemented.
See npcm7xx_emc.c for a list of unimplemented features.

Reviewed-by: Hao Wu <wuhaotsh@google.com>
Reviewed-by: Avi Fishman <avi.fishman@nuvoton.com>
Signed-off-by: Doug Evans <dje@google.com>
---
 hw/net/meson.build           |   1 +
 hw/net/npcm7xx_emc.c         | 852 +++++++++++++++++++++++++++++++++++
 hw/net/trace-events          |  17 +
 include/hw/net/npcm7xx_emc.h | 286 ++++++++++++
 4 files changed, 1156 insertions(+)
 create mode 100644 hw/net/npcm7xx_emc.c
 create mode 100644 include/hw/net/npcm7xx_emc.h

Comments

Peter Maydell Feb. 8, 2021, 5:17 p.m. UTC | #1
On Tue, 2 Feb 2021 at 23:29, Doug Evans <dje@google.com> wrote:
>
> This is a 10/100 ethernet device that has several features.
> Only the ones needed by the Linux driver have been implemented.
> See npcm7xx_emc.c for a list of unimplemented features.
>
> Reviewed-by: Hao Wu <wuhaotsh@google.com>
> Reviewed-by: Avi Fishman <avi.fishman@nuvoton.com>
> Signed-off-by: Doug Evans <dje@google.com>
> ---
>  hw/net/meson.build           |   1 +
>  hw/net/npcm7xx_emc.c         | 852 +++++++++++++++++++++++++++++++++++
>  hw/net/trace-events          |  17 +
>  include/hw/net/npcm7xx_emc.h | 286 ++++++++++++
>  4 files changed, 1156 insertions(+)
>  create mode 100644 hw/net/npcm7xx_emc.c
>  create mode 100644 include/hw/net/npcm7xx_emc.h

> +static void emc_reset(NPCM7xxEMCState *emc)
> +{
> +    trace_npcm7xx_emc_reset(emc->emc_num);
> +
> +    memset(&emc->regs[0], 0, sizeof(emc->regs));
> +
> +    /* These regs have non-zero reset values. */
> +    emc->regs[REG_TXDLSA] = 0xfffffffc;
> +    emc->regs[REG_RXDLSA] = 0xfffffffc;
> +    emc->regs[REG_MIIDA] = 0x00900000;
> +    emc->regs[REG_FFTCR] = 0x0101;
> +    emc->regs[REG_DMARFC] = 0x0800;
> +    emc->regs[REG_MPCNT] = 0x7fff;
> +
> +    emc->tx_active = false;
> +    emc->rx_active = false;
> +
> +    qemu_set_irq(emc->tx_irq, 0);
> +    qemu_set_irq(emc->rx_irq, 0);
> +}
> +
> +static void npcm7xx_emc_reset(DeviceState *dev)
> +{
> +    NPCM7xxEMCState *emc = NPCM7XX_EMC(dev);
> +    emc_reset(emc);
> +}

You can't call qemu_set_irq() from a DeviceState::reset method.
Usually it's OK just not to try to set the outbound IRQs and
to assume that the device you're connected to has reset to the
state where its inbound IRQ line is not asserted. If you really
need to set the irq line then you need to switch to 3-phase
reset (some of the other npcm7xx devices do this). But I
suspect that just moving the qemu_set_irq() calls to
emc_soft_reset() would be enough.

> +
> +static void emc_soft_reset(NPCM7xxEMCState *emc)
> +{
> +    /*
> +     * The docs say at least MCMDR.{LBK,OPMOD} bits are not changed during a
> +     * soft reset, but does not go into further detail. For now, KISS.
> +     */
> +    uint32_t mcmdr = emc->regs[REG_MCMDR];
> +    emc_reset(emc);
> +    emc->regs[REG_MCMDR] =
> +        mcmdr & (REG_MCMDR_LBK | REG_MCMDR_OPMOD);
> + }


> +static void emc_try_send_next_packet(NPCM7xxEMCState *emc)
> +{
> +    uint32_t desc_addr = TX_DESC_NTXDSA(emc->regs[REG_CTXDSA]);
> +    NPCM7xxEMCTxDesc tx_desc;
> +    if (emc_read_tx_desc(desc_addr, &tx_desc)) {
> +        /* Error reading descriptor, already reported. */
> +        emc_halt_tx(emc, REG_MISTA_TXBERR);
> +        emc_update_tx_irq(emc);
> +        return;
> +    }
> +
> +    /* Nothing we can do if we don't own the descriptor. */
> +    if (!(tx_desc.flags & TX_DESC_FLAG_OWNER_MASK)) {
> +        trace_npcm7xx_emc_cpu_owned_desc(desc_addr);
> +        emc_halt_tx(emc, REG_MISTA_TDU);
> +        emc_update_tx_irq(emc);
> +        return;
> +     }
> +
> +    /* Give the descriptor back regardless of what happens. */
> +    tx_desc.flags &= ~TX_DESC_FLAG_OWNER_MASK;
> +    tx_desc.status_and_length &= 0xffff;
> +
> +    /* Working buffer for sending out packets. Most packets fit in this. */
> +#define TX_BUFFER_SIZE 2048
> +    uint8_t tx_send_buffer[TX_BUFFER_SIZE];

Don't put local variable declarations in the middle of functions,
please. Coding style says they should be at the start of a
block (so, here, the start of the function). It looks like you've
got middle-of-function declarations in several places in other
functions too, so could you fix them all up please?

> +
> +    /*
> +     * Despite the h/w documentation saying the tx buffer is word aligned,
> +     * the linux driver does not word align the buffer. There is value in not
> +     * aligning the buffer: See the description of NET_IP_ALIGN in linux
> +     * kernel sources.
> +     */
> +    uint32_t next_buf_addr = tx_desc.txbsa;
> +    emc->regs[REG_CTXBSA] = next_buf_addr;
> +    uint32_t length = TX_DESC_PKT_LEN(tx_desc.status_and_length);
> +    uint8_t *buf = &tx_send_buffer[0];
> +    uint8_t *malloced_buf = NULL;

Optional, but you might consider using g_autofree for
malloced_buf, which would let the compiler deal with
g_free()ing it for you on all the function exit paths.

> +
> +    if (length > sizeof(tx_send_buffer)) {
> +        malloced_buf = g_malloc(length);
> +        buf = malloced_buf;
> +    }

Otherwise the patch looks OK I think.

thanks
-- PMM
Doug Evans Feb. 9, 2021, 1:25 a.m. UTC | #2
On Mon, Feb 8, 2021 at 9:17 AM Peter Maydell <peter.maydell@linaro.org>
wrote:

> On Tue, 2 Feb 2021 at 23:29, Doug Evans <dje@google.com> wrote:
> >
> > This is a 10/100 ethernet device that has several features.
> > Only the ones needed by the Linux driver have been implemented.
> > See npcm7xx_emc.c for a list of unimplemented features.
> >
> > Reviewed-by: Hao Wu <wuhaotsh@google.com>
> > Reviewed-by: Avi Fishman <avi.fishman@nuvoton.com>
> > Signed-off-by: Doug Evans <dje@google.com>
> > ---
> >  hw/net/meson.build           |   1 +
> >  hw/net/npcm7xx_emc.c         | 852 +++++++++++++++++++++++++++++++++++
> >  hw/net/trace-events          |  17 +
> >  include/hw/net/npcm7xx_emc.h | 286 ++++++++++++
> >  4 files changed, 1156 insertions(+)
> >  create mode 100644 hw/net/npcm7xx_emc.c
> >  create mode 100644 include/hw/net/npcm7xx_emc.h
>
> > +static void emc_reset(NPCM7xxEMCState *emc)
> > +{
> > +    trace_npcm7xx_emc_reset(emc->emc_num);
> > +
> > +    memset(&emc->regs[0], 0, sizeof(emc->regs));
> > +
> > +    /* These regs have non-zero reset values. */
> > +    emc->regs[REG_TXDLSA] = 0xfffffffc;
> > +    emc->regs[REG_RXDLSA] = 0xfffffffc;
> > +    emc->regs[REG_MIIDA] = 0x00900000;
> > +    emc->regs[REG_FFTCR] = 0x0101;
> > +    emc->regs[REG_DMARFC] = 0x0800;
> > +    emc->regs[REG_MPCNT] = 0x7fff;
> > +
> > +    emc->tx_active = false;
> > +    emc->rx_active = false;
> > +
> > +    qemu_set_irq(emc->tx_irq, 0);
> > +    qemu_set_irq(emc->rx_irq, 0);
> > +}
> > +
> > +static void npcm7xx_emc_reset(DeviceState *dev)
> > +{
> > +    NPCM7xxEMCState *emc = NPCM7XX_EMC(dev);
> > +    emc_reset(emc);
> > +}
>
> You can't call qemu_set_irq() from a DeviceState::reset method.
> Usually it's OK just not to try to set the outbound IRQs and
> to assume that the device you're connected to has reset to the
> state where its inbound IRQ line is not asserted. If you really
> need to set the irq line then you need to switch to 3-phase
> reset (some of the other npcm7xx devices do this). But I
> suspect that just moving the qemu_set_irq() calls to
> emc_soft_reset() would be enough.
>

Ah. Fixed in v3.

Don't put local variable declarations in the middle of functions,
> please. Coding style says they should be at the start of a
> block (so, here, the start of the function). It looks like you've
> got middle-of-function declarations in several places in other
> functions too, so could you fix them all up please?
>

Fixed in v3.
Maybe now's a good time though to revisit this rule.
QEMU uses C99, and mixed decls/statements is an easy improvement to the
coding standards.
I'm guessing this is an uncontroversial request. Is there just inertia
behind not making the change thus far?


> Optional, but you might consider using g_autofree for
> malloced_buf, which would let the compiler deal with
> g_free()ing it for you on all the function exit paths.
>

Done in v3.

Thanks.
Peter Maydell Feb. 9, 2021, 9:44 a.m. UTC | #3
On Tue, 9 Feb 2021 at 01:26, Doug Evans <dje@google.com> wrote:
> On Mon, Feb 8, 2021 at 9:17 AM Peter Maydell <peter.maydell@linaro.org> wrote:
>> Don't put local variable declarations in the middle of functions,
>> please. Coding style says they should be at the start of a
>> block (so, here, the start of the function). It looks like you've
>> got middle-of-function declarations in several places in other
>> functions too, so could you fix them all up please?
>
>
> Fixed in v3.
> Maybe now's a good time though to revisit this rule.
> QEMU uses C99, and mixed decls/statements is an easy improvement to the coding standards.
> I'm guessing this is an uncontroversial request. Is there just inertia behind not making the change thus far?

My personal opinion is that having declarations in the
middle of functions is uglier. CODING_STYLE.rst already
notes that we have an occasional-exception if there are
#ifdefs involved, so we don't have the style rule because
we're trying to work with compilers that don't accept
middle-of-block declarations.

thanks
-- PMM
diff mbox series

Patch

diff --git a/hw/net/meson.build b/hw/net/meson.build
index 4a7051b54a..af0749c42b 100644
--- a/hw/net/meson.build
+++ b/hw/net/meson.build
@@ -35,6 +35,7 @@  softmmu_ss.add(when: 'CONFIG_I82596_COMMON', if_true: files('i82596.c'))
 softmmu_ss.add(when: 'CONFIG_SUNHME', if_true: files('sunhme.c'))
 softmmu_ss.add(when: 'CONFIG_FTGMAC100', if_true: files('ftgmac100.c'))
 softmmu_ss.add(when: 'CONFIG_SUNGEM', if_true: files('sungem.c'))
+softmmu_ss.add(when: 'CONFIG_NPCM7XX', if_true: files('npcm7xx_emc.c'))
 
 softmmu_ss.add(when: 'CONFIG_ETRAXFS', if_true: files('etraxfs_eth.c'))
 softmmu_ss.add(when: 'CONFIG_COLDFIRE', if_true: files('mcf_fec.c'))
diff --git a/hw/net/npcm7xx_emc.c b/hw/net/npcm7xx_emc.c
new file mode 100644
index 0000000000..d7da1387b3
--- /dev/null
+++ b/hw/net/npcm7xx_emc.c
@@ -0,0 +1,852 @@ 
+/*
+ * Nuvoton NPCM7xx EMC Module
+ *
+ * Copyright 2020 Google LLC
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ *
+ * Unsupported/unimplemented features:
+ * - MCMDR.FDUP (full duplex) is ignored, half duplex is not supported
+ * - Only CAM0 is supported, CAM[1-15] are not
+ *   - writes to CAMEN.[1-15] are ignored, these bits always read as zeroes
+ * - MII is not implemented, MIIDA.BUSY and MIID always return zero
+ * - MCMDR.LBK is not implemented
+ * - MCMDR.{OPMOD,ENSQE,AEP,ARP} are not supported
+ * - H/W FIFOs are not supported, MCMDR.FFTCR is ignored
+ * - MGSTA.SQE is not supported
+ * - pause and control frames are not implemented
+ * - MGSTA.CCNT is not supported
+ * - MPCNT, DMARFS are not implemented
+ */
+
+#include "qemu/osdep.h"
+
+/* For crc32 */
+#include <zlib.h>
+
+#include "qemu-common.h"
+#include "hw/irq.h"
+#include "hw/qdev-clock.h"
+#include "hw/qdev-properties.h"
+#include "hw/net/npcm7xx_emc.h"
+#include "net/eth.h"
+#include "migration/vmstate.h"
+#include "qemu/bitops.h"
+#include "qemu/error-report.h"
+#include "qemu/log.h"
+#include "qemu/module.h"
+#include "qemu/units.h"
+#include "sysemu/dma.h"
+#include "trace.h"
+
+#define CRC_LENGTH 4
+
+/*
+ * The maximum size of a (layer 2) ethernet frame as defined by 802.3.
+ * 1518 = 6(dest macaddr) + 6(src macaddr) + 2(proto) + 4(crc) + 1500(payload)
+ * This does not include an additional 4 for the vlan field (802.1q).
+ */
+#define MAX_ETH_FRAME_SIZE 1518
+
+static const char *emc_reg_name(int regno)
+{
+#define REG(name) case REG_ ## name: return #name;
+    switch (regno) {
+    REG(CAMCMR)
+    REG(CAMEN)
+    REG(TXDLSA)
+    REG(RXDLSA)
+    REG(MCMDR)
+    REG(MIID)
+    REG(MIIDA)
+    REG(FFTCR)
+    REG(TSDR)
+    REG(RSDR)
+    REG(DMARFC)
+    REG(MIEN)
+    REG(MISTA)
+    REG(MGSTA)
+    REG(MPCNT)
+    REG(MRPC)
+    REG(MRPCC)
+    REG(MREPC)
+    REG(DMARFS)
+    REG(CTXDSA)
+    REG(CTXBSA)
+    REG(CRXDSA)
+    REG(CRXBSA)
+    case REG_CAMM_BASE + 0: return "CAM0M";
+    case REG_CAML_BASE + 0: return "CAM0L";
+    case REG_CAMM_BASE + 2 ... REG_CAMML_LAST:
+        /* Only CAM0 is supported, fold the others into something simple. */
+        if (regno & 1) {
+            return "CAM<n>L";
+        } else {
+            return "CAM<n>M";
+        }
+    default: return "UNKNOWN";
+    }
+#undef REG
+}
+
+static void emc_reset(NPCM7xxEMCState *emc)
+{
+    trace_npcm7xx_emc_reset(emc->emc_num);
+
+    memset(&emc->regs[0], 0, sizeof(emc->regs));
+
+    /* These regs have non-zero reset values. */
+    emc->regs[REG_TXDLSA] = 0xfffffffc;
+    emc->regs[REG_RXDLSA] = 0xfffffffc;
+    emc->regs[REG_MIIDA] = 0x00900000;
+    emc->regs[REG_FFTCR] = 0x0101;
+    emc->regs[REG_DMARFC] = 0x0800;
+    emc->regs[REG_MPCNT] = 0x7fff;
+
+    emc->tx_active = false;
+    emc->rx_active = false;
+
+    qemu_set_irq(emc->tx_irq, 0);
+    qemu_set_irq(emc->rx_irq, 0);
+}
+
+static void npcm7xx_emc_reset(DeviceState *dev)
+{
+    NPCM7xxEMCState *emc = NPCM7XX_EMC(dev);
+    emc_reset(emc);
+}
+
+static void emc_soft_reset(NPCM7xxEMCState *emc)
+{
+    /*
+     * The docs say at least MCMDR.{LBK,OPMOD} bits are not changed during a
+     * soft reset, but does not go into further detail. For now, KISS.
+     */
+    uint32_t mcmdr = emc->regs[REG_MCMDR];
+    emc_reset(emc);
+    emc->regs[REG_MCMDR] =
+        mcmdr & (REG_MCMDR_LBK | REG_MCMDR_OPMOD);
+}
+
+static void emc_set_link(NetClientState *nc)
+{
+    /* Nothing to do yet. */
+}
+
+/* MISTA.TXINTR is the union of the individual bits with their enables. */
+static void emc_update_mista_txintr(NPCM7xxEMCState *emc)
+{
+    /* Only look at the bits we support. */
+    uint32_t mask = (REG_MISTA_TXBERR |
+                     REG_MISTA_TDU |
+                     REG_MISTA_TXCP);
+    if (emc->regs[REG_MISTA] & emc->regs[REG_MIEN] & mask) {
+        emc->regs[REG_MISTA] |= REG_MISTA_TXINTR;
+    } else {
+        emc->regs[REG_MISTA] &= ~REG_MISTA_TXINTR;
+    }
+}
+
+/* MISTA.RXINTR is the union of the individual bits with their enables. */
+static void emc_update_mista_rxintr(NPCM7xxEMCState *emc)
+{
+    /* Only look at the bits we support. */
+    uint32_t mask = (REG_MISTA_RXBERR |
+                     REG_MISTA_RDU |
+                     REG_MISTA_RXGD);
+    if (emc->regs[REG_MISTA] & emc->regs[REG_MIEN] & mask) {
+        emc->regs[REG_MISTA] |= REG_MISTA_RXINTR;
+    } else {
+        emc->regs[REG_MISTA] &= ~REG_MISTA_RXINTR;
+    }
+}
+
+/* N.B. emc_update_mista_txintr must have already been called. */
+static void emc_update_tx_irq(NPCM7xxEMCState *emc)
+{
+    int level = !!(emc->regs[REG_MISTA] &
+                   emc->regs[REG_MIEN] &
+                   REG_MISTA_TXINTR);
+    trace_npcm7xx_emc_update_tx_irq(level);
+    qemu_set_irq(emc->tx_irq, level);
+}
+
+/* N.B. emc_update_mista_rxintr must have already been called. */
+static void emc_update_rx_irq(NPCM7xxEMCState *emc)
+{
+    int level = !!(emc->regs[REG_MISTA] &
+                   emc->regs[REG_MIEN] &
+                   REG_MISTA_RXINTR);
+    trace_npcm7xx_emc_update_rx_irq(level);
+    qemu_set_irq(emc->rx_irq, level);
+}
+
+/* Update IRQ states due to changes in MIEN,MISTA. */
+static void emc_update_irq_from_reg_change(NPCM7xxEMCState *emc)
+{
+    emc_update_mista_txintr(emc);
+    emc_update_tx_irq(emc);
+
+    emc_update_mista_rxintr(emc);
+    emc_update_rx_irq(emc);
+}
+
+static int emc_read_tx_desc(dma_addr_t addr, NPCM7xxEMCTxDesc *desc)
+{
+    if (dma_memory_read(&address_space_memory, addr, desc, sizeof(*desc))) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Failed to read descriptor @ 0x%"
+                      HWADDR_PRIx "\n", __func__, addr);
+        return -1;
+    }
+    desc->flags = le32_to_cpu(desc->flags);
+    desc->txbsa = le32_to_cpu(desc->txbsa);
+    desc->status_and_length = le32_to_cpu(desc->status_and_length);
+    desc->ntxdsa = le32_to_cpu(desc->ntxdsa);
+    return 0;
+}
+
+static int emc_write_tx_desc(const NPCM7xxEMCTxDesc *desc, dma_addr_t addr)
+{
+    NPCM7xxEMCTxDesc le_desc;
+
+    le_desc.flags = cpu_to_le32(desc->flags);
+    le_desc.txbsa = cpu_to_le32(desc->txbsa);
+    le_desc.status_and_length = cpu_to_le32(desc->status_and_length);
+    le_desc.ntxdsa = cpu_to_le32(desc->ntxdsa);
+    if (dma_memory_write(&address_space_memory, addr, &le_desc,
+                         sizeof(le_desc))) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Failed to write descriptor @ 0x%"
+                      HWADDR_PRIx "\n", __func__, addr);
+        return -1;
+    }
+    return 0;
+}
+
+static int emc_read_rx_desc(dma_addr_t addr, NPCM7xxEMCRxDesc *desc)
+{
+    if (dma_memory_read(&address_space_memory, addr, desc, sizeof(*desc))) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Failed to read descriptor @ 0x%"
+                      HWADDR_PRIx "\n", __func__, addr);
+        return -1;
+    }
+    desc->status_and_length = le32_to_cpu(desc->status_and_length);
+    desc->rxbsa = le32_to_cpu(desc->rxbsa);
+    desc->reserved = le32_to_cpu(desc->reserved);
+    desc->nrxdsa = le32_to_cpu(desc->nrxdsa);
+    return 0;
+}
+
+static int emc_write_rx_desc(const NPCM7xxEMCRxDesc *desc, dma_addr_t addr)
+{
+    NPCM7xxEMCRxDesc le_desc;
+
+    le_desc.status_and_length = cpu_to_le32(desc->status_and_length);
+    le_desc.rxbsa = cpu_to_le32(desc->rxbsa);
+    le_desc.reserved = cpu_to_le32(desc->reserved);
+    le_desc.nrxdsa = cpu_to_le32(desc->nrxdsa);
+    if (dma_memory_write(&address_space_memory, addr, &le_desc,
+                         sizeof(le_desc))) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Failed to write descriptor @ 0x%"
+                      HWADDR_PRIx "\n", __func__, addr);
+        return -1;
+    }
+    return 0;
+}
+
+static void emc_set_mista(NPCM7xxEMCState *emc, uint32_t flags)
+{
+    trace_npcm7xx_emc_set_mista(flags);
+    emc->regs[REG_MISTA] |= flags;
+    if (extract32(flags, 16, 16)) {
+        emc_update_mista_txintr(emc);
+    }
+    if (extract32(flags, 0, 16)) {
+        emc_update_mista_rxintr(emc);
+    }
+}
+
+static void emc_halt_tx(NPCM7xxEMCState *emc, uint32_t mista_flag)
+{
+    emc->tx_active = false;
+    emc_set_mista(emc, mista_flag);
+}
+
+static void emc_halt_rx(NPCM7xxEMCState *emc, uint32_t mista_flag)
+{
+    emc->rx_active = false;
+    emc_set_mista(emc, mista_flag);
+}
+
+static void emc_set_next_tx_descriptor(NPCM7xxEMCState *emc,
+                                       const NPCM7xxEMCTxDesc *tx_desc,
+                                       uint32_t desc_addr)
+{
+    /* Update the current descriptor, if only to reset the owner flag. */
+    if (emc_write_tx_desc(tx_desc, desc_addr)) {
+        /*
+         * We just read it so this shouldn't generally happen.
+         * Error already reported.
+         */
+        emc_set_mista(emc, REG_MISTA_TXBERR);
+    }
+    emc->regs[REG_CTXDSA] = TX_DESC_NTXDSA(tx_desc->ntxdsa);
+}
+
+static void emc_set_next_rx_descriptor(NPCM7xxEMCState *emc,
+                                       const NPCM7xxEMCRxDesc *rx_desc,
+                                       uint32_t desc_addr)
+{
+    /* Update the current descriptor, if only to reset the owner flag. */
+    if (emc_write_rx_desc(rx_desc, desc_addr)) {
+        /*
+         * We just read it so this shouldn't generally happen.
+         * Error already reported.
+         */
+        emc_set_mista(emc, REG_MISTA_RXBERR);
+    }
+    emc->regs[REG_CRXDSA] = RX_DESC_NRXDSA(rx_desc->nrxdsa);
+}
+
+static void emc_try_send_next_packet(NPCM7xxEMCState *emc)
+{
+    uint32_t desc_addr = TX_DESC_NTXDSA(emc->regs[REG_CTXDSA]);
+    NPCM7xxEMCTxDesc tx_desc;
+    if (emc_read_tx_desc(desc_addr, &tx_desc)) {
+        /* Error reading descriptor, already reported. */
+        emc_halt_tx(emc, REG_MISTA_TXBERR);
+        emc_update_tx_irq(emc);
+        return;
+    }
+
+    /* Nothing we can do if we don't own the descriptor. */
+    if (!(tx_desc.flags & TX_DESC_FLAG_OWNER_MASK)) {
+        trace_npcm7xx_emc_cpu_owned_desc(desc_addr);
+        emc_halt_tx(emc, REG_MISTA_TDU);
+        emc_update_tx_irq(emc);
+        return;
+     }
+
+    /* Give the descriptor back regardless of what happens. */
+    tx_desc.flags &= ~TX_DESC_FLAG_OWNER_MASK;
+    tx_desc.status_and_length &= 0xffff;
+
+    /* Working buffer for sending out packets. Most packets fit in this. */
+#define TX_BUFFER_SIZE 2048
+    uint8_t tx_send_buffer[TX_BUFFER_SIZE];
+
+    /*
+     * Despite the h/w documentation saying the tx buffer is word aligned,
+     * the linux driver does not word align the buffer. There is value in not
+     * aligning the buffer: See the description of NET_IP_ALIGN in linux
+     * kernel sources.
+     */
+    uint32_t next_buf_addr = tx_desc.txbsa;
+    emc->regs[REG_CTXBSA] = next_buf_addr;
+    uint32_t length = TX_DESC_PKT_LEN(tx_desc.status_and_length);
+    uint8_t *buf = &tx_send_buffer[0];
+    uint8_t *malloced_buf = NULL;
+
+    if (length > sizeof(tx_send_buffer)) {
+        malloced_buf = g_malloc(length);
+        buf = malloced_buf;
+    }
+
+    if (dma_memory_read(&address_space_memory, next_buf_addr, buf, length)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Failed to read packet @ 0x%x\n",
+                      __func__, next_buf_addr);
+        emc_set_mista(emc, REG_MISTA_TXBERR);
+        g_free(malloced_buf);
+        emc_set_next_tx_descriptor(emc, &tx_desc, desc_addr);
+        emc_update_tx_irq(emc);
+        trace_npcm7xx_emc_tx_done(emc->regs[REG_CTXDSA]);
+        return;
+    }
+
+    if ((tx_desc.flags & TX_DESC_FLAG_PADEN) && (length < MIN_PACKET_LENGTH)) {
+        memset(buf + length, 0, MIN_PACKET_LENGTH - length);
+        length = MIN_PACKET_LENGTH;
+    }
+
+    /* N.B. emc_receive can get called here. */
+    qemu_send_packet(qemu_get_queue(emc->nic), buf, length);
+    trace_npcm7xx_emc_sent_packet(length);
+    g_free(malloced_buf);
+    malloced_buf = buf = NULL;
+
+    tx_desc.status_and_length |= TX_DESC_STATUS_TXCP;
+    if (tx_desc.flags & TX_DESC_FLAG_INTEN) {
+        emc_set_mista(emc, REG_MISTA_TXCP);
+    }
+    if (emc->regs[REG_MISTA] & emc->regs[REG_MIEN] & REG_MISTA_TXINTR) {
+        tx_desc.status_and_length |= TX_DESC_STATUS_TXINTR;
+    }
+
+    emc_set_next_tx_descriptor(emc, &tx_desc, desc_addr);
+    emc_update_tx_irq(emc);
+    trace_npcm7xx_emc_tx_done(emc->regs[REG_CTXDSA]);
+}
+
+static bool emc_can_receive(NetClientState *nc)
+{
+    NPCM7xxEMCState *emc = NPCM7XX_EMC(qemu_get_nic_opaque(nc));
+
+    bool can_receive = emc->rx_active;
+    trace_npcm7xx_emc_can_receive(can_receive);
+    return can_receive;
+}
+
+/* If result is false then *fail_reason contains the reason. */
+static bool emc_receive_filter1(NPCM7xxEMCState *emc, const uint8_t *buf,
+                                size_t len, const char **fail_reason)
+{
+    eth_pkt_types_e pkt_type = get_eth_packet_type(PKT_GET_ETH_HDR(buf));
+
+    switch (pkt_type) {
+    case ETH_PKT_BCAST:
+        if (emc->regs[REG_CAMCMR] & REG_CAMCMR_CCAM) {
+            return true;
+        } else {
+            *fail_reason = "Broadcast packet disabled";
+            return !!(emc->regs[REG_CAMCMR] & REG_CAMCMR_ABP);
+        }
+    case ETH_PKT_MCAST:
+        if (emc->regs[REG_CAMCMR] & REG_CAMCMR_CCAM) {
+            return true;
+        } else {
+            *fail_reason = "Multicast packet disabled";
+            return !!(emc->regs[REG_CAMCMR] & REG_CAMCMR_AMP);
+        }
+    case ETH_PKT_UCAST: {
+        if (emc->regs[REG_CAMCMR] & REG_CAMCMR_AUP) {
+            return true;
+        }
+        bool matches = ((emc->regs[REG_CAMCMR] & REG_CAMCMR_ECMP) &&
+                        /* We only support one CAM register, CAM0. */
+                        (emc->regs[REG_CAMEN] & (1 << 0)) &&
+                        memcmp(buf, emc->conf.macaddr.a, ETH_ALEN) == 0);
+        if (emc->regs[REG_CAMCMR] & REG_CAMCMR_CCAM) {
+            *fail_reason = "MACADDR matched, comparison complemented";
+            return !matches;
+        } else {
+            *fail_reason = "MACADDR didn't match";
+            return matches;
+        }
+    }
+    default:
+        g_assert_not_reached();
+    }
+}
+
+static bool emc_receive_filter(NPCM7xxEMCState *emc, const uint8_t *buf,
+                               size_t len)
+{
+    const char *fail_reason = NULL;
+    bool ok = emc_receive_filter1(emc, buf, len, &fail_reason);
+    if (!ok) {
+        trace_npcm7xx_emc_packet_filtered_out(fail_reason);
+    }
+    return ok;
+}
+
+static ssize_t emc_receive(NetClientState *nc, const uint8_t *buf, size_t len1)
+{
+    NPCM7xxEMCState *emc = NPCM7XX_EMC(qemu_get_nic_opaque(nc));
+    const uint32_t len = len1;
+
+    trace_npcm7xx_emc_receiving_packet(len);
+
+    if (!emc_can_receive(nc)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Unexpected packet\n", __func__);
+        return -1;
+    }
+
+    if (len < ETH_HLEN ||
+        /* Defensive programming: drop unsupportable large packets. */
+        len > 0xffff - CRC_LENGTH) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Dropped frame of %u bytes\n",
+                      __func__, len);
+        return len;
+    }
+
+    /*
+     * DENI is set if EMC received the Length/Type field of the incoming
+     * packet, so it will be set regardless of what happens next.
+     */
+    emc_set_mista(emc, REG_MISTA_DENI);
+
+    if (!emc_receive_filter(emc, buf, len)) {
+        emc_update_rx_irq(emc);
+        return len;
+    }
+
+    /* Huge frames (> DMARFC) are dropped. */
+    size_t max_frame_len = REG_DMARFC_RXMS(emc->regs[REG_DMARFC]);
+    if (len + CRC_LENGTH > max_frame_len) {
+        trace_npcm7xx_emc_packet_dropped(len);
+        emc_set_mista(emc, REG_MISTA_DFOI);
+        emc_update_rx_irq(emc);
+        return len;
+    }
+
+    /*
+     * Long Frames (> MAX_ETH_FRAME_SIZE) are also dropped, unless MCMDR.ALP
+     * is set.
+     */
+    bool long_frame = false;
+    if (len + CRC_LENGTH > MAX_ETH_FRAME_SIZE) {
+        if (emc->regs[REG_MCMDR] & REG_MCMDR_ALP) {
+            long_frame = true;
+        } else {
+            trace_npcm7xx_emc_packet_dropped(len);
+            emc_set_mista(emc, REG_MISTA_PTLE);
+            emc_update_rx_irq(emc);
+            return len;
+        }
+    }
+
+    uint32_t desc_addr = RX_DESC_NRXDSA(emc->regs[REG_CRXDSA]);
+    NPCM7xxEMCRxDesc rx_desc;
+    if (emc_read_rx_desc(desc_addr, &rx_desc)) {
+        /* Error reading descriptor, already reported. */
+        emc_halt_rx(emc, REG_MISTA_RXBERR);
+        emc_update_rx_irq(emc);
+        return len;
+    }
+
+    /* Nothing we can do if we don't own the descriptor. */
+    if (!(rx_desc.status_and_length & RX_DESC_STATUS_OWNER_MASK)) {
+        trace_npcm7xx_emc_cpu_owned_desc(desc_addr);
+        emc_halt_rx(emc, REG_MISTA_RDU);
+        emc_update_rx_irq(emc);
+        return len;
+    }
+
+    uint32_t crc = 0;
+    uint8_t *crc_ptr = (uint8_t *) &crc;
+    if (!(emc->regs[REG_MCMDR] & REG_MCMDR_SPCRC)) {
+        crc = cpu_to_be32(crc32(~0, buf, len));
+    }
+
+    /* Give the descriptor back regardless of what happens. */
+    rx_desc.status_and_length &= ~RX_DESC_STATUS_OWNER_MASK;
+
+    uint32_t buf_addr = rx_desc.rxbsa;
+    emc->regs[REG_CRXBSA] = buf_addr;
+    if (dma_memory_write(&address_space_memory, buf_addr, buf, len) ||
+        (!(emc->regs[REG_MCMDR] & REG_MCMDR_SPCRC) &&
+         dma_memory_write(&address_space_memory, buf_addr + len, crc_ptr,
+                          4))) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Bus error writing packet\n",
+                      __func__);
+        emc_set_mista(emc, REG_MISTA_RXBERR);
+        emc_set_next_rx_descriptor(emc, &rx_desc, desc_addr);
+        emc_update_rx_irq(emc);
+        trace_npcm7xx_emc_rx_done(emc->regs[REG_CRXDSA]);
+        return len;
+    }
+
+    trace_npcm7xx_emc_received_packet(len);
+
+    /* Note: We've already verified len+4 <= 0xffff. */
+    rx_desc.status_and_length = len;
+    if (!(emc->regs[REG_MCMDR] & REG_MCMDR_SPCRC)) {
+        rx_desc.status_and_length += 4;
+    }
+    rx_desc.status_and_length |= RX_DESC_STATUS_RXGD;
+    emc_set_mista(emc, REG_MISTA_RXGD);
+
+    if (emc->regs[REG_MISTA] & emc->regs[REG_MIEN] & REG_MISTA_RXINTR) {
+        rx_desc.status_and_length |= RX_DESC_STATUS_RXINTR;
+    }
+    if (long_frame) {
+        rx_desc.status_and_length |= RX_DESC_STATUS_PTLE;
+    }
+
+    emc_set_next_rx_descriptor(emc, &rx_desc, desc_addr);
+    emc_update_rx_irq(emc);
+    trace_npcm7xx_emc_rx_done(emc->regs[REG_CRXDSA]);
+    return len;
+}
+
+static void emc_try_receive_next_packet(NPCM7xxEMCState *emc)
+{
+    if (emc_can_receive(qemu_get_queue(emc->nic))) {
+        qemu_flush_queued_packets(qemu_get_queue(emc->nic));
+    }
+}
+
+static uint64_t npcm7xx_emc_read(void *opaque, hwaddr offset, unsigned size)
+{
+    NPCM7xxEMCState *emc = opaque;
+    uint32_t reg = offset / sizeof(uint32_t);
+
+    if (reg >= NPCM7XX_NUM_EMC_REGS) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: Invalid offset 0x%04" HWADDR_PRIx "\n",
+                      __func__, offset);
+        return 0;
+    }
+
+    uint32_t result;
+
+    switch (reg) {
+    case REG_MIID:
+        /*
+         * We don't implement MII. For determinism, always return zero as
+         * writes record the last value written for debugging purposes.
+         */
+        qemu_log_mask(LOG_UNIMP, "%s: Read of MIID, returning 0\n", __func__);
+        result = 0;
+        break;
+    case REG_TSDR:
+    case REG_RSDR:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: Read of write-only reg, %s/%d\n",
+                      __func__, emc_reg_name(reg), reg);
+        return 0;
+    default:
+        result = emc->regs[reg];
+        break;
+    }
+
+    trace_npcm7xx_emc_reg_read(emc->emc_num, result, emc_reg_name(reg), reg);
+    return result;
+}
+
+static void npcm7xx_emc_write(void *opaque, hwaddr offset,
+                              uint64_t v, unsigned size)
+{
+    NPCM7xxEMCState *emc = opaque;
+    uint32_t reg = offset / sizeof(uint32_t);
+    uint32_t value = v;
+
+    g_assert(size == sizeof(uint32_t));
+
+    if (reg >= NPCM7XX_NUM_EMC_REGS) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: Invalid offset 0x%04" HWADDR_PRIx "\n",
+                      __func__, offset);
+        return;
+    }
+
+    trace_npcm7xx_emc_reg_write(emc->emc_num, emc_reg_name(reg), reg, value);
+
+    switch (reg) {
+    case REG_CAMCMR:
+        emc->regs[reg] = value;
+        break;
+    case REG_CAMEN:
+        /* Only CAM0 is supported, don't pretend otherwise. */
+        if (value & ~1) {
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "%s: Only CAM0 is supported, cannot enable others"
+                          ": 0x%x\n",
+                          __func__, value);
+        }
+        emc->regs[reg] = value & 1;
+        break;
+    case REG_CAMM_BASE + 0:
+        emc->regs[reg] = value;
+        emc->conf.macaddr.a[0] = value >> 24;
+        emc->conf.macaddr.a[1] = value >> 16;
+        emc->conf.macaddr.a[2] = value >> 8;
+        emc->conf.macaddr.a[3] = value >> 0;
+        break;
+    case REG_CAML_BASE + 0:
+        emc->regs[reg] = value;
+        emc->conf.macaddr.a[4] = value >> 24;
+        emc->conf.macaddr.a[5] = value >> 16;
+        break;
+    case REG_MCMDR: {
+        if (value & REG_MCMDR_SWR) {
+            emc_soft_reset(emc);
+            /* On h/w the reset happens over multiple cycles. For now KISS. */
+            break;
+        }
+        uint32_t prev = emc->regs[reg];
+        emc->regs[reg] = value;
+        /* Update tx state. */
+        if (!(prev & REG_MCMDR_TXON) &&
+            (value & REG_MCMDR_TXON)) {
+            emc->regs[REG_CTXDSA] = emc->regs[REG_TXDLSA];
+            /*
+             * Linux kernel turns TX on with CPU still holding descriptor,
+             * which suggests we should wait for a write to TSDR before trying
+             * to send a packet: so we don't send one here.
+             */
+        } else if ((prev & REG_MCMDR_TXON) &&
+                   !(value & REG_MCMDR_TXON)) {
+            emc->regs[REG_MGSTA] |= REG_MGSTA_TXHA;
+        }
+        if (!(value & REG_MCMDR_TXON)) {
+            emc_halt_tx(emc, 0);
+        }
+        /* Update rx state. */
+        if (!(prev & REG_MCMDR_RXON) &&
+            (value & REG_MCMDR_RXON)) {
+            emc->regs[REG_CRXDSA] = emc->regs[REG_RXDLSA];
+        } else if ((prev & REG_MCMDR_RXON) &&
+                   !(value & REG_MCMDR_RXON)) {
+            emc->regs[REG_MGSTA] |= REG_MGSTA_RXHA;
+        }
+        if (!(value & REG_MCMDR_RXON)) {
+            emc_halt_rx(emc, 0);
+        }
+        break;
+    }
+    case REG_TXDLSA:
+    case REG_RXDLSA:
+    case REG_DMARFC:
+    case REG_MIID:
+        emc->regs[reg] = value;
+        break;
+    case REG_MIEN:
+        emc->regs[reg] = value;
+        emc_update_irq_from_reg_change(emc);
+        break;
+    case REG_MISTA:
+        /* Clear the bits that have 1 in "value". */
+        emc->regs[reg] &= ~value;
+        emc_update_irq_from_reg_change(emc);
+        break;
+    case REG_MGSTA:
+        /* Clear the bits that have 1 in "value". */
+        emc->regs[reg] &= ~value;
+        break;
+    case REG_TSDR:
+        if (emc->regs[REG_MCMDR] & REG_MCMDR_TXON) {
+            emc->tx_active = true;
+            /* Keep trying to send packets until we run out. */
+            while (emc->tx_active) {
+                emc_try_send_next_packet(emc);
+            }
+        }
+        break;
+    case REG_RSDR:
+        if (emc->regs[REG_MCMDR] & REG_MCMDR_RXON) {
+            emc->rx_active = true;
+            emc_try_receive_next_packet(emc);
+        }
+        break;
+    case REG_MIIDA:
+        emc->regs[reg] = value & ~REG_MIIDA_BUSY;
+        break;
+    case REG_MRPC:
+    case REG_MRPCC:
+    case REG_MREPC:
+    case REG_CTXDSA:
+    case REG_CTXBSA:
+    case REG_CRXDSA:
+    case REG_CRXBSA:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: Write to read-only reg %s/%d\n",
+                      __func__, emc_reg_name(reg), reg);
+        break;
+    default:
+        qemu_log_mask(LOG_UNIMP, "%s: Write to unimplemented reg %s/%d\n",
+                      __func__, emc_reg_name(reg), reg);
+        break;
+    }
+}
+
+static const struct MemoryRegionOps npcm7xx_emc_ops = {
+    .read = npcm7xx_emc_read,
+    .write = npcm7xx_emc_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid = {
+        .min_access_size = 4,
+        .max_access_size = 4,
+        .unaligned = false,
+    },
+};
+
+static void emc_cleanup(NetClientState *nc)
+{
+    /* Nothing to do yet. */
+}
+
+static NetClientInfo net_npcm7xx_emc_info = {
+    .type = NET_CLIENT_DRIVER_NIC,
+    .size = sizeof(NICState),
+    .can_receive = emc_can_receive,
+    .receive = emc_receive,
+    .cleanup = emc_cleanup,
+    .link_status_changed = emc_set_link,
+};
+
+static void npcm7xx_emc_realize(DeviceState *dev, Error **errp)
+{
+    NPCM7xxEMCState *emc = NPCM7XX_EMC(dev);
+    SysBusDevice *sbd = SYS_BUS_DEVICE(emc);
+
+    memory_region_init_io(&emc->iomem, OBJECT(emc), &npcm7xx_emc_ops, emc,
+                          TYPE_NPCM7XX_EMC, 4 * KiB);
+    sysbus_init_mmio(sbd, &emc->iomem);
+    sysbus_init_irq(sbd, &emc->tx_irq);
+    sysbus_init_irq(sbd, &emc->rx_irq);
+
+    qemu_macaddr_default_if_unset(&emc->conf.macaddr);
+    emc->nic = qemu_new_nic(&net_npcm7xx_emc_info, &emc->conf,
+                            object_get_typename(OBJECT(dev)), dev->id, emc);
+    qemu_format_nic_info_str(qemu_get_queue(emc->nic), emc->conf.macaddr.a);
+}
+
+static void npcm7xx_emc_unrealize(DeviceState *dev)
+{
+    NPCM7xxEMCState *emc = NPCM7XX_EMC(dev);
+
+    qemu_del_nic(emc->nic);
+}
+
+static const VMStateDescription vmstate_npcm7xx_emc = {
+    .name = TYPE_NPCM7XX_EMC,
+    .version_id = 0,
+    .minimum_version_id = 0,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT8(emc_num, NPCM7xxEMCState),
+        VMSTATE_UINT32_ARRAY(regs, NPCM7xxEMCState, NPCM7XX_NUM_EMC_REGS),
+        VMSTATE_BOOL(tx_active, NPCM7xxEMCState),
+        VMSTATE_BOOL(rx_active, NPCM7xxEMCState),
+        VMSTATE_END_OF_LIST(),
+    },
+};
+
+static Property npcm7xx_emc_properties[] = {
+    DEFINE_NIC_PROPERTIES(NPCM7xxEMCState, conf),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void npcm7xx_emc_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    set_bit(DEVICE_CATEGORY_NETWORK, dc->categories);
+    dc->desc = "NPCM7xx EMC Controller";
+    dc->realize = npcm7xx_emc_realize;
+    dc->unrealize = npcm7xx_emc_unrealize;
+    dc->reset = npcm7xx_emc_reset;
+    dc->vmsd = &vmstate_npcm7xx_emc;
+    device_class_set_props(dc, npcm7xx_emc_properties);
+}
+
+static const TypeInfo npcm7xx_emc_info = {
+    .name = TYPE_NPCM7XX_EMC,
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(NPCM7xxEMCState),
+    .class_init = npcm7xx_emc_class_init,
+};
+
+static void npcm7xx_emc_register_type(void)
+{
+    type_register_static(&npcm7xx_emc_info);
+}
+
+type_init(npcm7xx_emc_register_type)
diff --git a/hw/net/trace-events b/hw/net/trace-events
index 5db45456d9..baf25ffa7e 100644
--- a/hw/net/trace-events
+++ b/hw/net/trace-events
@@ -429,3 +429,20 @@  imx_fec_receive_last(int last) "rx frame flags 0x%04x"
 imx_enet_receive(size_t size) "len %zu"
 imx_enet_receive_len(uint64_t addr, int len) "rx_bd 0x%"PRIx64" length %d"
 imx_enet_receive_last(int last) "rx frame flags 0x%04x"
+
+# npcm7xx_emc.c
+npcm7xx_emc_reset(int emc_num) "Resetting emc%d"
+npcm7xx_emc_update_tx_irq(int level) "Setting tx irq to %d"
+npcm7xx_emc_update_rx_irq(int level) "Setting rx irq to %d"
+npcm7xx_emc_set_mista(uint32_t flags) "ORing 0x%x into MISTA"
+npcm7xx_emc_cpu_owned_desc(uint32_t addr) "Can't process cpu-owned descriptor @0x%x"
+npcm7xx_emc_sent_packet(uint32_t len) "Sent %u byte packet"
+npcm7xx_emc_tx_done(uint32_t ctxdsa) "TX done, CTXDSA=0x%x"
+npcm7xx_emc_can_receive(int can_receive) "Can receive: %d"
+npcm7xx_emc_packet_filtered_out(const char* fail_reason) "Packet filtered out: %s"
+npcm7xx_emc_packet_dropped(uint32_t len) "%u byte packet dropped"
+npcm7xx_emc_receiving_packet(uint32_t len) "Receiving %u byte packet"
+npcm7xx_emc_received_packet(uint32_t len) "Received %u byte packet"
+npcm7xx_emc_rx_done(uint32_t crxdsa) "RX done, CRXDSA=0x%x"
+npcm7xx_emc_reg_read(int emc_num, uint32_t result, const char *name, int regno) "emc%d: 0x%x = reg[%s/%d]"
+npcm7xx_emc_reg_write(int emc_num, const char *name, int regno, uint32_t value) "emc%d: reg[%s/%d] = 0x%x"
diff --git a/include/hw/net/npcm7xx_emc.h b/include/hw/net/npcm7xx_emc.h
new file mode 100644
index 0000000000..eac7f29816
--- /dev/null
+++ b/include/hw/net/npcm7xx_emc.h
@@ -0,0 +1,286 @@ 
+/*
+ * Nuvoton NPCM7xx EMC Module
+ *
+ * Copyright 2020 Google LLC
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ */
+
+#ifndef NPCM7XX_EMC_H
+#define NPCM7XX_EMC_H
+
+#include "hw/irq.h"
+#include "hw/sysbus.h"
+#include "net/net.h"
+
+/* 32-bit register indices. */
+enum NPCM7xxPWMRegister {
+    /* Control registers. */
+    REG_CAMCMR,
+    REG_CAMEN,
+
+    /* There are 16 CAMn[ML] registers. */
+    REG_CAMM_BASE,
+    REG_CAML_BASE,
+    REG_CAMML_LAST = 0x21,
+
+    REG_TXDLSA = 0x22,
+    REG_RXDLSA,
+    REG_MCMDR,
+    REG_MIID,
+    REG_MIIDA,
+    REG_FFTCR,
+    REG_TSDR,
+    REG_RSDR,
+    REG_DMARFC,
+    REG_MIEN,
+
+    /* Status registers. */
+    REG_MISTA,
+    REG_MGSTA,
+    REG_MPCNT,
+    REG_MRPC,
+    REG_MRPCC,
+    REG_MREPC,
+    REG_DMARFS,
+    REG_CTXDSA,
+    REG_CTXBSA,
+    REG_CRXDSA,
+    REG_CRXBSA,
+
+    NPCM7XX_NUM_EMC_REGS,
+};
+
+/* REG_CAMCMR fields */
+/* Enable CAM Compare */
+#define REG_CAMCMR_ECMP (1 << 4)
+/* Complement CAM Compare */
+#define REG_CAMCMR_CCAM (1 << 3)
+/* Accept Broadcast Packet */
+#define REG_CAMCMR_ABP (1 << 2)
+/* Accept Multicast Packet */
+#define REG_CAMCMR_AMP (1 << 1)
+/* Accept Unicast Packet */
+#define REG_CAMCMR_AUP (1 << 0)
+
+/* REG_MCMDR fields */
+/* Software Reset */
+#define REG_MCMDR_SWR (1 << 24)
+/* Internal Loopback Select */
+#define REG_MCMDR_LBK (1 << 21)
+/* Operation Mode Select */
+#define REG_MCMDR_OPMOD (1 << 20)
+/* Enable MDC Clock Generation */
+#define REG_MCMDR_ENMDC (1 << 19)
+/* Full-Duplex Mode Select */
+#define REG_MCMDR_FDUP (1 << 18)
+/* Enable SQE Checking */
+#define REG_MCMDR_ENSEQ (1 << 17)
+/* Send PAUSE Frame */
+#define REG_MCMDR_SDPZ (1 << 16)
+/* No Defer */
+#define REG_MCMDR_NDEF (1 << 9)
+/* Frame Transmission On */
+#define REG_MCMDR_TXON (1 << 8)
+/* Strip CRC Checksum */
+#define REG_MCMDR_SPCRC (1 << 5)
+/* Accept CRC Error Packet */
+#define REG_MCMDR_AEP (1 << 4)
+/* Accept Control Packet */
+#define REG_MCMDR_ACP (1 << 3)
+/* Accept Runt Packet */
+#define REG_MCMDR_ARP (1 << 2)
+/* Accept Long Packet */
+#define REG_MCMDR_ALP (1 << 1)
+/* Frame Reception On */
+#define REG_MCMDR_RXON (1 << 0)
+
+/* REG_MIEN fields */
+/* Enable Transmit Descriptor Unavailable Interrupt */
+#define REG_MIEN_ENTDU (1 << 23)
+/* Enable Transmit Completion Interrupt */
+#define REG_MIEN_ENTXCP (1 << 18)
+/* Enable Transmit Interrupt */
+#define REG_MIEN_ENTXINTR (1 << 16)
+/* Enable Receive Descriptor Unavailable Interrupt */
+#define REG_MIEN_ENRDU (1 << 10)
+/* Enable Receive Good Interrupt */
+#define REG_MIEN_ENRXGD (1 << 4)
+/* Enable Receive Interrupt */
+#define REG_MIEN_ENRXINTR (1 << 0)
+
+/* REG_MISTA fields */
+/* TODO: Add error fields and support simulated errors? */
+/* Transmit Bus Error Interrupt */
+#define REG_MISTA_TXBERR (1 << 24)
+/* Transmit Descriptor Unavailable Interrupt */
+#define REG_MISTA_TDU (1 << 23)
+/* Transmit Completion Interrupt */
+#define REG_MISTA_TXCP (1 << 18)
+/* Transmit Interrupt */
+#define REG_MISTA_TXINTR (1 << 16)
+/* Receive Bus Error Interrupt */
+#define REG_MISTA_RXBERR (1 << 11)
+/* Receive Descriptor Unavailable Interrupt */
+#define REG_MISTA_RDU (1 << 10)
+/* DMA Early Notification Interrupt */
+#define REG_MISTA_DENI (1 << 9)
+/* Maximum Frame Length Interrupt */
+#define REG_MISTA_DFOI (1 << 8)
+/* Receive Good Interrupt */
+#define REG_MISTA_RXGD (1 << 4)
+/* Packet Too Long Interrupt */
+#define REG_MISTA_PTLE (1 << 3)
+/* Receive Interrupt */
+#define REG_MISTA_RXINTR (1 << 0)
+
+/* REG_MGSTA fields */
+/* Transmission Halted */
+#define REG_MGSTA_TXHA (1 << 11)
+/* Receive Halted */
+#define REG_MGSTA_RXHA (1 << 11)
+
+/* REG_DMARFC fields */
+/* Maximum Receive Frame Length */
+#define REG_DMARFC_RXMS(word) extract32((word), 0, 16)
+
+/* REG MIIDA fields */
+/* Busy Bit */
+#define REG_MIIDA_BUSY (1 << 17)
+
+/* Transmit and receive descriptors */
+typedef struct NPCM7xxEMCTxDesc NPCM7xxEMCTxDesc;
+typedef struct NPCM7xxEMCRxDesc NPCM7xxEMCRxDesc;
+
+struct NPCM7xxEMCTxDesc {
+    uint32_t flags;
+    uint32_t txbsa;
+    uint32_t status_and_length;
+    uint32_t ntxdsa;
+};
+
+struct NPCM7xxEMCRxDesc {
+    uint32_t status_and_length;
+    uint32_t rxbsa;
+    uint32_t reserved;
+    uint32_t nrxdsa;
+};
+
+/* NPCM7xxEMCTxDesc.flags values */
+/* Owner: 0 = cpu, 1 = emc */
+#define TX_DESC_FLAG_OWNER_MASK (1 << 31)
+/* Transmit interrupt enable */
+#define TX_DESC_FLAG_INTEN (1 << 2)
+/* CRC append */
+#define TX_DESC_FLAG_CRCAPP (1 << 1)
+/* Padding enable */
+#define TX_DESC_FLAG_PADEN (1 << 0)
+
+/* NPCM7xxEMCTxDesc.status_and_length values */
+/* Collision count */
+#define TX_DESC_STATUS_CCNT_SHIFT 28
+#define TX_DESC_STATUS_CCNT_BITSIZE 4
+/* SQE error */
+#define TX_DESC_STATUS_SQE (1 << 26)
+/* Transmission paused */
+#define TX_DESC_STATUS_PAU (1 << 25)
+/* P transmission halted */
+#define TX_DESC_STATUS_TXHA (1 << 24)
+/* Late collision */
+#define TX_DESC_STATUS_LC (1 << 23)
+/* Transmission abort */
+#define TX_DESC_STATUS_TXABT (1 << 22)
+/* No carrier sense */
+#define TX_DESC_STATUS_NCS (1 << 21)
+/* Defer exceed */
+#define TX_DESC_STATUS_EXDEF (1 << 20)
+/* Transmission complete */
+#define TX_DESC_STATUS_TXCP (1 << 19)
+/* Transmission deferred */
+#define TX_DESC_STATUS_DEF (1 << 17)
+/* Transmit interrupt */
+#define TX_DESC_STATUS_TXINTR (1 << 16)
+
+#define TX_DESC_PKT_LEN(word) extract32((word), 0, 16)
+
+/* Transmit buffer start address */
+#define TX_DESC_TXBSA(word) ((uint32_t) (word) & ~3u)
+
+/* Next transmit descriptor start address */
+#define TX_DESC_NTXDSA(word) ((uint32_t) (word) & ~3u)
+
+/* NPCM7xxEMCRxDesc.status_and_length values */
+/* Owner: 0b00 = cpu, 0b01 = undefined, 0b10 = emc, 0b11 = undefined */
+#define RX_DESC_STATUS_OWNER_SHIFT 30
+#define RX_DESC_STATUS_OWNER_BITSIZE 2
+#define RX_DESC_STATUS_OWNER_MASK (3 << RX_DESC_STATUS_OWNER_SHIFT)
+/* Runt packet */
+#define RX_DESC_STATUS_RP (1 << 22)
+/* Alignment error */
+#define RX_DESC_STATUS_ALIE (1 << 21)
+/* Frame reception complete */
+#define RX_DESC_STATUS_RXGD (1 << 20)
+/* Packet too long */
+#define RX_DESC_STATUS_PTLE (1 << 19)
+/* CRC error */
+#define RX_DESC_STATUS_CRCE (1 << 17)
+/* Receive interrupt */
+#define RX_DESC_STATUS_RXINTR (1 << 16)
+
+#define RX_DESC_PKT_LEN(word) extract32((word), 0, 16)
+
+/* Receive buffer start address */
+#define RX_DESC_RXBSA(word) ((uint32_t) (word) & ~3u)
+
+/* Next receive descriptor start address */
+#define RX_DESC_NRXDSA(word) ((uint32_t) (word) & ~3u)
+
+/* Minimum packet length, when TX_DESC_FLAG_PADEN is set. */
+#define MIN_PACKET_LENGTH 64
+
+struct NPCM7xxEMCState {
+    /*< private >*/
+    SysBusDevice parent;
+    /*< public >*/
+
+    MemoryRegion iomem;
+
+    qemu_irq tx_irq;
+    qemu_irq rx_irq;
+
+    NICState *nic;
+    NICConf conf;
+
+    /* 0 or 1, for log messages */
+    uint8_t emc_num;
+
+    uint32_t regs[NPCM7XX_NUM_EMC_REGS];
+
+    /*
+     * tx is active. Set to true by TSDR and then switches off when out of
+     * descriptors. If the TXON bit in REG_MCMDR is off then this is off.
+     */
+    bool tx_active;
+
+    /*
+     * rx is active. Set to true by RSDR and then switches off when out of
+     * descriptors. If the RXON bit in REG_MCMDR is off then this is off.
+     */
+    bool rx_active;
+};
+
+typedef struct NPCM7xxEMCState NPCM7xxEMCState;
+
+#define TYPE_NPCM7XX_EMC "npcm7xx-emc"
+#define NPCM7XX_EMC(obj) \
+    OBJECT_CHECK(NPCM7xxEMCState, (obj), TYPE_NPCM7XX_EMC)
+
+#endif /* NPCM7XX_EMC_H */