On 2012-12-13 14:28, Sekhar Nori wrote: > 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.
Like I wrote in patch, my DM6443 based card behaves the same. > 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 It says that timer registers are protected by hardware when the timer is active. I guess writes are ignored if timer is active. Regards, /Thomas _______________________________________________ Davinci-linux-open-source mailing list Davinci-linux-open-source@linux.davincidsp.com http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source
