@@ -28,9 +28,11 @@ and a
here.
A transfer may consist of multiple messages and is started with a START condition and ends with a STOP condition as described in the I2C specification.
Messages within the transfer are concatenated using the REPEATED START condition which is described there as well.
-Some devices keep their internal states for REPEATED START but reset them after a STOP.
-Also, you cannot be interrupted by another I2C master during one transfer, but it might happen between multiple transfers.
-This programm helps you to create proper transfers for your needs.
+There are some advantages of having multiple messages in one transfer.
+First, some devices keep their internal states for REPEATED START but reset them after a STOP.
+Second, you cannot get interrupted during one transfer, but it might happen between multiple transfers.
+Interruption could happen on hardware level by another I2C master on the bus, or at software level by another I2C user who got its transfer scheduled between yours.
+This program helps you to create proper transfers for your needs.
.SH OPTIONS
.TP
@@ -71,7 +73,10 @@ This number should correspond to one of the busses listed by
.PP
The next parameter is one or multiple
.I desc
-blocks which is composed like this:
+blocks.
+The number of blocks is limited by the Linux Kernel and defined in I2C_RDWR_IOCTL_MAX_MSGS (42 as of v4.10).
+.I desc
+blocks are composed like this:
.I {r|w}<length_of_message>[@address]
@@ -81,16 +86,17 @@ specifies if the message is read or write
.TP
.B <length_of_message>
specifies the number of bytes read or written in this message.
-It is parsed as an unsigned 16 bit integer, but note that the Linux might apply an additional upper limit (8192 as of v4.10).
+It is parsed as an unsigned 16 bit integer, but note that the Linux Kernel apply an additional upper limit (8192 as of v4.10).
.TP
.B [@address]
-specifies the address of the chip to be accessed for this message, and is an integer.
+specifies the 7-bit address of the chip to be accessed for this message, and is an integer.
If omitted, reuse the previous address.
Normally, addresses outside the range of 0x03-0x77 and addresses with a kernel driver attached to them will be blocked.
With
.I -f
(force), all addresses can be used.
Be very careful when using that!
+10-bit addresses are currently not supported at all.
.PP
If the I2C message is a write, then a
@@ -112,7 +118,7 @@ increase value by 1 until end of message (i.e. 0+ means 0, 1, 2, ...)
decrease value by 1 until end of message (i.e. 0xff- means 0xff, 0xfe, 0xfd, ...)
.TP
p
-use value as seed for an 8 bit pseudo random sequence (i.e. 0p means 0x00, 0x50, 0xb0, ..)
+use value as seed for an 8 bit pseudo random sequence (i.e. 0p means 0x00, 0x50, 0xb0, ...)
.SH EXAMPLES
.PP
@@ -124,7 +130,7 @@ On bus 0, from an EEPROM at address 0x50, read 8 byte from offset 0x64
.RE
.fi
.PP
-For the same eeprom, at offset 0x42 write 0xff 0xfe .. 0xf0
+For the same EEPROM, at offset 0x42 write 0xff 0xfe ... 0xf0
(one write message; first byte sets the memory pointer to 0x42, 0xff is the first data byte, all following data bytes are decreased by one):
.nf
.RS
@@ -49,10 +49,11 @@ static void help(void)
" DATA are LENGTH bytes for a write message. They can be shortened by a suffix:\n"
" = (keep value constant until LENGTH)\n"
" + (increase value by 1 until LENGTH)\n"
- " - (decrease value by 1 until LENGTH)\n\n"
- "Example (bus 0, read 8 byte at offset 0x64 from eeprom at 0x50):\n"
+ " - (decrease value by 1 until LENGTH)\n"
+ " p (use pseudo random generator until LENGTH with value as seed)\n\n"
+ "Example (bus 0, read 8 byte at offset 0x64 from EEPROM at 0x50):\n"
" # i2ctransfer 0 w1@0x50 0x64 r8\n"
- "Example (same eeprom, at offset 0x42 write 0xff 0xfe .. 0xf0):\n"
+ "Example (same EEPROM, at offset 0x42 write 0xff 0xfe ... 0xf0):\n"
" # i2ctransfer 0 w17@0x50 0x42 0xff-\n");
}