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Ticket #1515 (new defect)

Opened 14 years ago

Last modified 14 years ago

Time stamp counter is imprecise

Reported by: hoene@uni-tuebingen.de Assigned to:
Priority: minor Milestone:
Component: madwifi: other Version: v0.9.3.2
Keywords: Cc:
Patch is attached: 0 Pending:

Description

On some Atheros chips >AR5212 such as the "AR5006X 802.11abg NIC (rev 01)", the timestamp counter (TSF) is too slow by about 250 ppm. That means, the mactime clock of the WLAN card misses about 1ms in 4s. If you do TOA distance measurements, this error is significant.

Attachments

Bildschirmphoto1.png (98.2 kB) - added by hoene@uni-tuebingen.de on 08/21/07 17:40:56.
Picture done with my measurement tool

Change History

08/21/07 17:40:56 changed by hoene@uni-tuebingen.de

  • attachment Bildschirmphoto1.png added.

Picture done with my measurement tool

(follow-up: ↓ 2 ) 08/21/07 18:39:46 changed by mentor

What are you using as a reference clock?

(in reply to: ↑ 1 ; follow-up: ↓ 3 ) 09/24/07 22:01:02 changed by anonymous

Replying to mentor:

What are you using as a reference clock?

I used a couple of other WLAN card as reference clock such as older Atheros cards, Intel and Prisms. Usually, the clock drift must does not extend +-20 ppm. Does, I am 100% sure that my measurements are valid and that the TSF values are too slow.

In addition, I have checked the standard, which states that the TSF must have a precision of -+100ppm. Thus, Atheros does not comply to the standard ;-)

(in reply to: ↑ 2 ) 05/22/08 16:23:47 changed by mah@cs.umd.edu

This appears to be a hardware issue that the driver cannot fix.

06/03/08 09:07:44 changed by Christian

Are where any changes that Atheros will read this web page and will answer to it?

06/03/08 11:35:47 changed by anonymous

no.... this is just a tracer for driver problems. but not for silicon bugs.