On Wed, Sep 15, 2010 at 12:30 PM, Bruno Randolf <br1@xxxxxxxxxxx> wrote:
> On Wed September 15 2010 10:56:32 Jonathan Guerin wrote:
>> 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
>>
>> In the driver source, this appears to be initialised to:
>>
>> $$ ath5k.h
>> #define AR5K_INIT_ACK_CTS_TIMEOUT 1024
>>
>> $$ reg.h
>> /*
>> * ACK/CTS timeout register
>> */
>> #define AR5K_TIME_OUT 0x8014 /* Register Address */
>> #define AR5K_TIME_OUT_ACK 0x00001fff /* ACK timeout mask */
>> #define AR5K_TIME_OUT_ACK_S 0
>> #define AR5K_TIME_OUT_CTS 0x1fff0000 /* CTS timeout mask */
>> #define AR5K_TIME_OUT_CTS_S 16
>>
>> Taking the value of the register (1024), masking it with the ACK
>> Timeout Mask (0x1fff) and dividing it by the clock rate (40), we get a
>> much smaller ACK Timeout value:
>> 1024 & 0x1fff = 1024
>> 1024/40 = 25us
>>
>>
>> Am I understanding this right? Is the driver actually setting the ACK
>> Timeout to be much smaller than even a DIFS, let alone matching the
>> spec?
>>
>
> thanks for looking into this! i think you are right in that there is a mistake
> here, but AR5K_INIT_ACK_CTS_TIMEOUT is just used for AR5210 chips for setting
> the AR5K_SLOT_TIME. so this is wrong, but it probably does not affect you (or
I did realise after posting my message that the value was being
written into the SLOT_TIME register, rather than the TIME_OUT one. My
bad, I should've done a more thorough search...
> many people). 5211 and 5212 only use initvals:
>
> /* a aTurbo b g (OFDM) */
> 5211:
> { AR5K_TIME_OUT,
> { 0x04000400, 0x08000800, 0x20003000, 0x04000400 } },
>
> 5212:
> { AR5K_TIME_OUT,
> { 0x03e803e8, 0x06e006e0, 0x04200420, 0x08400840, 0x06e006e0 } },
>
> so on 5211 this is 1024 in A and G mode (i dont care about B and turbo), so
> same problem you described.
>
> on 5212 this is 1000 in A mode and 1760 in G mode, which would result in a
> timeout of 25 and 40.
We have a 5213 chip - does this default to the 5212 branch inside ath5k?
>
> this is all confusing and i think we should replace the initvals by calling
> the function ath5k_hw_set_ack_timeout().
Should all of the init be changed to use these functions, along with
#define init values?
>
> bruno
>
Thanks,
Jonathan
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