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
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.
this is all confusing and i think we should replace the initvals by calling
the function ath5k_hw_set_ack_timeout().
bruno
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