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[3/3] vivid sdr: fix broken sine tone generated for sdr FM

Message ID 1423040852-7470-4-git-send-email-hverkuil@xs4all.nl (mailing list archive)
State New, archived
Headers show

Commit Message

Hans Verkuil Feb. 4, 2015, 9:07 a.m. UTC 
From: Prashant Laddha <prladdha@cisco.com>

FM (frequency modulated) signal for SDR is generated by varying the
phase, where phase variation is proportional to input signal. It is
seen that, the larger phase increments leads to discontinuities in
the signal recovered after demodulation. Reducing the extent of phase
variation with respect to input signal, equivalent to reducing the
modulation index.

Tested using FM receiver flow graph in gnuradio-companion.

Cc: Antti Palosaari <crope@iki.fi>
Signed-off-by: Prashant Laddha <prladdha@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
---
 drivers/media/platform/vivid/vivid-sdr-cap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/drivers/media/platform/vivid/vivid-sdr-cap.c b/drivers/media/platform/vivid/vivid-sdr-cap.c
index 5e089cb..caf1316 100644
--- a/drivers/media/platform/vivid/vivid-sdr-cap.c
+++ b/drivers/media/platform/vivid/vivid-sdr-cap.c
@@ -454,7 +454,7 @@  void vivid_sdr_cap_process(struct vivid_dev *dev, struct vivid_buffer *buf)
 						FIXP_2PI) >> (31 - FIXP_N);
 
 		dev->sdr_fixp_src_phase += src_phase_step;
-		dev->sdr_fixp_mod_phase += mod_phase_step;
+		dev->sdr_fixp_mod_phase += mod_phase_step / 4;
 
 		/*
 		 * Transfer phases to [0 / 2xPI] in order to avoid variable