FM (frequency modulated) signal for SDR is generated by varying the phase. The phase variation is proportional to input signal. It was observed that, the larger phase increments leads to discontinuties in the signal recovered after demodulation. This was one of the reason for broken (cracky) sine tone after SDR receiver.
This patch modifies the phase calculation on two counts - 1. Phase of modulated signal, is varied around a center value. 2. The extent of phase variation with respect to input signal is reduced. This is equivalent to reducing modulation index. FM signal generated using modifed equation, do not lead to broken sine tone. Cc: Hans Verkuil <[email protected]> Cc: Antti Palosaari <[email protected]> Signed-off-by: Prashant Laddha <[email protected]> --- drivers/media/platform/vivid/vivid-sdr-cap.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/media/platform/vivid/vivid-sdr-cap.c b/drivers/media/platform/vivid/vivid-sdr-cap.c index 1e5abd7..1e77771 100644 --- a/drivers/media/platform/vivid/vivid-sdr-cap.c +++ b/drivers/media/platform/vivid/vivid-sdr-cap.c @@ -455,7 +455,9 @@ void vivid_sdr_cap_process(struct vivid_dev *dev, struct vivid_buffer *buf) for (i = 0; i < plane_size; i += 2) { - mod_phase_inc = calc_cos(dev->sdr_fixp_src_phase); + mod_phase_inc = calc_cos(dev->sdr_fixp_src_phase) / 4 + + src_phase_inc; + dev->sdr_fixp_src_phase += src_phase_inc; while (dev->sdr_fixp_src_phase >= FIX_PT_2PI) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
