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Subject: [media] tda18271c2dd: Fix saw filter configuration for DVB-6 @ 6MHz Author: Mauro Carvalho Chehab <[email protected]> Date: Thu Jul 28 15:49:43 2011 -0300 Currently, the driver assumes that all QAM carriers are spaced with 8MHz. This is wrong, and may decrease QoS on Countries like Brazil, that have DVB-C carriers with 6MHz-spaced. Fortunately, both ITU-T J-83 and EN 300 429 specifies a way to associate the symbol rate with the bandwidth needed for it. For ITU-T J-83 2007 annex A, the maximum symbol rate for 6 MHz is: 6 MHz / 1.15 = 5217391 Bauds For ITU-T J-83 2007 annex C, the maximum symbol rate for 6 MHz is: 6 MHz / 1.13 = 5309735 Bauds. As this tuner is currently used only for DRX-K, and it is currently hard-coded to annex A, I've opted to use the roll-off factor of 0.15, instead of 0.13. If we ever support annex C, the better would be to add a DVB S2API call to allow changing between Annex A and C, and add the 0.13 roll-off factor to it. This code is currently being used on other frontends, so I think we should later add a core function with this code, to warrant that it will be properly implemented everywhere. Signed-off-by: Mauro Carvalho Chehab <[email protected]> drivers/media/dvb/frontends/tda18271c2dd.c | 20 +++++++++++++++++++- 1 files changed, 19 insertions(+), 1 deletions(-) --- http://git.linuxtv.org/media_tree.git?a=commitdiff;h=8068868c607e8cceeb6c8943309202ee74ef5b35 diff --git a/drivers/media/dvb/frontends/tda18271c2dd.c b/drivers/media/dvb/frontends/tda18271c2dd.c index 2eb3a31..0384e8d 100644 --- a/drivers/media/dvb/frontends/tda18271c2dd.c +++ b/drivers/media/dvb/frontends/tda18271c2dd.c @@ -1123,6 +1123,21 @@ static int release(struct dvb_frontend *fe) return 0; } +/* + * As defined on EN 300 429 Annex A and on ITU-T J.83 annex A, the DVB-C + * roll-off factor is 0.15. + * According with the specs, the amount of the needed bandwith is given by: + * Bw = Symbol_rate * (1 + 0.15) + * As such, the maximum symbol rate supported by 6 MHz is + * max_symbol_rate = 6 MHz / 1.15 = 5217391 Bauds + *NOTE: For ITU-T J.83 Annex C, the roll-off factor is 0.13. So: + * max_symbol_rate = 6 MHz / 1.13 = 5309735 Baud + * That means that an adjustment is needed for Japan, + * but, as currently DRX-K is hardcoded to Annex A, let's stick + * with 0.15 roll-off factor. + */ +#define MAX_SYMBOL_RATE_6MHz 5217391 + static int set_params(struct dvb_frontend *fe, struct dvb_frontend_parameters *params) { @@ -1146,7 +1161,10 @@ static int set_params(struct dvb_frontend *fe, break; } else if (fe->ops.info.type == FE_QAM) { - Standard = HF_DVBC_8MHZ; + if (params->u.qam.symbol_rate <= MAX_SYMBOL_RATE_6MHz) + Standard = HF_DVBC_6MHZ; + else + Standard = HF_DVBC_8MHZ; } else return -EINVAL; do { _______________________________________________ linuxtv-commits mailing list [email protected] http://www.linuxtv.org/cgi-bin/mailman/listinfo/linuxtv-commits
