On 12/13/2012 2:17 AM, Thomas Lange wrote: > The time drift problem I have been chasing for a while, see > http://linux.davincidsp.com/pipermail/davinci-linux-open-source/2012-December/025821.html > , seems to be due to an undocumented silicon bug. > > The attached patch to master ( c22cf7755db6500df037cecdd6b290394d82392e > Origin: git://gitorious.org/linux-davinci/linux-davinci.git ) > exercises the problem. Example console output from my EVM6446 card: > > ---------------- > Before T0:0x5ed55a T1:0x5ed55d Diff:-3 > After T0:0x5ed817 T1:0x5ed824 Diff:-13 > Before T0:0x62a7e5 T1:0x62a7f3 Diff:-14 > After T0:0x62adff T1:0x62ae17 Diff:-24 > Before T0:0x66cbfb T1:0x66cc14 Diff:-25 > After T0:0x66d1f6 T1:0x66d219 Diff:-35 > Before T0:0x6aeab0 T1:0x6aead4 Diff:-36 > After T0:0x6af0ec T1:0x6af11a Diff:-46 > Before T0:0x6f09ef T1:0x6f0a1e Diff:-47 > After T0:0x6f1018 T1:0x6f1051 Diff:-57 > Before T0:0x732821 T1:0x73285b Diff:-58 > After T0:0x732e1a T1:0x732e5e Diff:-68 > --------------- > > This shows that TIM34_0 misses 11 ticks every time a new event is setup > (10 ticks from my test loop + the original code 1). > > If someone from TI can verify that the problem exists in all Davinci > versions, a workaround should be pretty straightforward, assuming this > is the only symptom of the bug.
I was not able to spend too much time on this today, but I did try your patch on my DM644x EVM and have observations similar to what you describe above. Further, I see that reading TIM12 instead of writing it does not cause the same drift on TIM34. I still need to try on a different DaVinci device. One thing to try would be to temporarily stop both TIM12_0 and TIM34_0 using ENAMODE bits in TCR before resetting TIM12_0. There is a cryptic note about writes to timer register being disallowed when timer is running in section 2.4.2 of http://www.ti.com/lit/ug/sprue26/sprue26.pdf Thanks, Sekhar _______________________________________________ Davinci-linux-open-source mailing list Davinci-linux-open-source@linux.davincidsp.com http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source
