On Wed, Nov 24, 2010 at 11:35 AM, Jonathan Guerin <jonathan@xxxxxxxxxxxx> wrote: > On Wed, Nov 24, 2010 at 11:04 AM, Nick Kossifidis <mickflemm@xxxxxxxxx> wrote: >> 2010/11/24 Nick Kossifidis <mickflemm@xxxxxxxxx>: >>> 2010/11/24 Jonathan Guerin <jonathan@xxxxxxxxxxxx>: >>>> On Wed, Nov 24, 2010 at 5:09 AM, Nick Kossifidis <mickflemm@xxxxxxxxx> wrote: >>>>> * Extend get_default_sifs/slot_time to include timings for turbo >>>>> half and quarter rate modes. >>>>> >>>>> * AR5210 code for now uses timings already on core clock units >>>>> instead of usecs so rename them (we 'll clean it up later). >>>>> >>>>> Signed-off-by: Nick Kossifidis <mickflemm@xxxxxxxxx> >>>>> --- >>>>> drivers/net/wireless/ath/ath5k/ath5k.h | 24 ++++++++++++-- >>>>> drivers/net/wireless/ath/ath5k/pcu.c | 52 ++++++++++++++++++++++++-------- >>>>> drivers/net/wireless/ath/ath5k/qcu.c | 16 +++++---- >>>>> 3 files changed, 68 insertions(+), 24 deletions(-) >>>>> >>>>> diff --git a/drivers/net/wireless/ath/ath5k/ath5k.h b/drivers/net/wireless/ath/ath5k/ath5k.h >>>>> index 005cad0..e11fc8f 100644 >>>>> --- a/drivers/net/wireless/ath/ath5k/ath5k.h >>>>> +++ b/drivers/net/wireless/ath/ath5k/ath5k.h >>>>> @@ -226,16 +226,16 @@ >>>>> #define AR5K_INIT_USEC 39 >>>>> #define AR5K_INIT_USEC_TURBO 79 >>>>> #define AR5K_INIT_USEC_32 31 >>>>> -#define AR5K_INIT_SLOT_TIME 396 >>>>> -#define AR5K_INIT_SLOT_TIME_TURBO 480 >>>>> +#define AR5K_INIT_SLOT_TIME_CLOCK 396 >>>> >>>> This comes out as 9.9us (with a clock multiplier of 40), rather than 9 >>>> - should be 360? >>>> >>>>> +#define AR5K_INIT_SLOT_TIME_TURBO_CLOCK 480 >>>>> #define AR5K_INIT_ACK_CTS_TIMEOUT 1024 >>>> >>>> From a previous post I'd made: >>>> >>>> According to the 802.11-2007 spec document, the ACKTimeout value is >>>> (Section 9.2.8 ACK procedure): >>>> ACKTimeout = aSIFSTime + aSlotTime + aPHY-RX-START-Delay >>>> >>>> From Table 17-15—OFDM PHY characteristics, the values are: >>>> aSIFSTime = 16 >>>> aSlotTime = 9 >>>> aPHY-RX-START-Delay = 25 >>>> >>>> Therefore, ACKTimeout = 50 >>>> >>>> With a value of 1024, the ACKTIMEOUT is actually 25. >>>> >>>>> #define AR5K_INIT_ACK_CTS_TIMEOUT_TURBO 0x08000800 >>>>> #define AR5K_INIT_PROG_IFS 920 >>>>> #define AR5K_INIT_PROG_IFS_TURBO 960 >>>>> #define AR5K_INIT_EIFS 3440 >>>> >>>> From the 802.11-2007 Spec (9.2.10 DCF timing relations): >>>> The EIFS is derived from the SIFS and the DIFS and the length of time >>>> it takes to transmit an ACK Control frame at the lowest PHY mandatory >>>> rate by the following equation: >>>> EIFS = aSIFSTime + DIFS + ACKTxTime >>>> where ACKTxTime is the time expressed in microseconds required to >>>> transmit an ACK frame, including >>>> preamble, PLCP header and any additional PHY dependent information, at >>>> the lowest PHY mandatory rate. >>>> >>>> So, EIFS = 16 + 32 + 44 (ACKTX @ 24Mbps) = 92 >>>> or 16 + 32 + 60 (ACKTX @ 6Mbps) = 108 >>>> >>>> The current value is 86, which I guess is a nice midpoint, but is >>>> there any reasoning for this value? It should really be set to the >>>> longest value of 108, as an EIFS is only used when we have no >>>> information about a frame because it failed the checksum. >>>> >>>>> #define AR5K_INIT_EIFS_TURBO 6880 >>>>> -#define AR5K_INIT_SIFS 560 >>>>> -#define AR5K_INIT_SIFS_TURBO 480 >>>>> +#define AR5K_INIT_SIFS_CLOCK 560 >>>> >>>> This is wrong, when you divide by the clock rate, you get a SIFS of 14, not 16. >>>> >>>> Cheers, >>>> >>>> Jonathan >>>> >>> >>> All _CLOCK variables are left here temporarily until we clean up >>> AR5210 stuff later, i know it's wrong ;-) >>> Check out patch 16 that adds the new set_ifs_intervals, there we set >>> them property, i just left them here so that code can still compile. >>> >> >> Also have in mind that clock on g is not 40 but 44 (for b >> compatibility) so 396 is correct here (396/44 = 9). >> >> Anyway we clean it up + these are only for AR5210 that we still don't >> support, i just put a _CLOCK prefix so that they don't get mixed up >> with the correct definitions. Check out patch 16, it should be fine >> ;-) > > Oops, my bad on the clock rate. So, for A mode, it's 40, and G mode, > 44, or 44 for both? > > If that's the case, then some of the values are still wrong (they're > also wrong in patch 16): > > EIFS = 3440 / 44 = 78, which is way shorter than it should be! This > gives ath5k an advantage over other 802.11-2007-compliant stations. > > ACK/CTS TIMEOUT = 1024/44 = 23, which is still much, much shorter than > the required 50us, once again giving ath5k an advantage for medium > contention. > > SIFS = 560/44 = 12, which is shorter again than the required 16us! > > Not saying your work is bad, by the way, but just that the values have > been wrong in ath5k for a while. :) > > Cheers, > > Jonathan Never mind, I didn't read Patch 16 properly... :( Cheers, Jonathan >> >> >> -- >> GPG ID: 0xD21DB2DB >> As you read this post global entropy rises. Have Fun ;-) >> Nick >> > -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
