While trying to deal with errata i856 on the dra7xx I encountered some obvious typos in the frequencies checked in timer.c, so those are being fixed in case anyone ever tries to use one of them. Also implement a fix for errata i856. Without the fix the time on the system will get ahead by 43 seconds per day if SYSCLK1 is 20MHz, which it is on the EVM boards as well as the other boards I am currently aware of. ntp declares that the system time drifts by over 500ppm (the maximum ntp will tolerate). To fix it, check the status register to determine if the 32.768KHz clock source is real (driven by an external crystal) or emulated (SYSCLK1 / 610), and if it is emulated use the appropriate numerator and divisor to make the fine master counter match the coarse master counter (which is driven directly from the 32KHz clock (real or emulated) with a fixed multiplier of 375 / 2). Making the fine counter run at a frequency different from the coarse counter is not an option, as the value in the fine counter is updated to match the coarse counter if they ever get out of sync. With 19.2MHz installed on the board, the clock runs almost 5% slow. With the change in place, ntp runs with a drift of around 3ppm on all boards I have tried which is well within the spec of the crystals used for SYSCLK1. Even if the errata is fixed in future revisions of the chip, there is still the option of someone purposely not connecting a 32.768KHz crystal to save cost or board space, and relying on the emulated clock instead, in which case this correction will still be necessary. Len Sorensen (2): ARM: omap5/dra7xx: Fix frequency typos. ARM: dra7xx: Fix counter frequency drift for AM572x errata i856. arch/arm/mach-omap2/control.h | 4 ++++ arch/arm/mach-omap2/timer.c | 44 +++++++++++++++++++++++++++++++++++------ 2 files changed, 42 insertions(+), 6 deletions(-) -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
