diff options
| author | Mauro Carvalho Chehab <mchehab@redhat.com> | 2013-04-07 21:11:53 -0300 |
|---|---|---|
| committer | Mauro Carvalho Chehab <mchehab@redhat.com> | 2013-04-08 07:12:44 -0300 |
| commit | 752a62b2ec9c21931dce869f2ae2c921c83a1164 (patch) | |
| tree | 2cbcebc4cd623a187a1c6c2d6b55075a71790e72 /drivers | |
| parent | 0562aef296c251e50b0934e6af113c511349dd9c (diff) | |
[media] cx24123: improve precision when calculating symbol rate ratio
Symbol rate ratio were using a rough calculus, as the code was
limited to 32 bits arithmetic. Change it to 64 bits, in order
to better estimate the bandwidth low-pass filter on the demod.
This should reduce the noise and improve reception.
Reported-by: Hans-Peter Jansen <hpj@urpla.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/media/dvb-frontends/cx24123.c | 28 |
1 files changed, 7 insertions, 21 deletions
diff --git a/drivers/media/dvb-frontends/cx24123.c b/drivers/media/dvb-frontends/cx24123.c index 68c88ab58e7..a771da3e9f9 100644 --- a/drivers/media/dvb-frontends/cx24123.c +++ b/drivers/media/dvb-frontends/cx24123.c @@ -26,6 +26,7 @@ #include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> +#include <asm/div64.h> #include "dvb_frontend.h" #include "cx24123.h" @@ -452,7 +453,8 @@ static u32 cx24123_int_log2(u32 a, u32 b) static int cx24123_set_symbolrate(struct cx24123_state *state, u32 srate) { - u32 tmp, sample_rate, ratio, sample_gain; + u64 tmp; + u32 sample_rate, ratio, sample_gain; u8 pll_mult; /* check if symbol rate is within limits */ @@ -482,27 +484,11 @@ static int cx24123_set_symbolrate(struct cx24123_state *state, u32 srate) sample_rate = pll_mult * XTAL; - /* - SYSSymbolRate[21:0] = (srate << 23) / sample_rate - - We have to use 32 bit unsigned arithmetic without precision loss. - The maximum srate is 45000000 or 0x02AEA540. This number has - only 6 clear bits on top, hence we can shift it left only 6 bits - at a time. Borrowed from cx24110.c - */ - - tmp = srate << 6; - ratio = tmp / sample_rate; - - tmp = (tmp % sample_rate) << 6; - ratio = (ratio << 6) + (tmp / sample_rate); - - tmp = (tmp % sample_rate) << 6; - ratio = (ratio << 6) + (tmp / sample_rate); - - tmp = (tmp % sample_rate) << 5; - ratio = (ratio << 5) + (tmp / sample_rate); + /* SYSSymbolRate[21:0] = (srate << 23) / sample_rate */ + tmp = ((u64)srate) << 23; + do_div(tmp, sample_rate); + ratio = (u32) tmp; cx24123_writereg(state, 0x01, pll_mult * 6); |