AM335x Watchdog in Linux via memory map

Hi Rico,

See this wiki: http://processors.wiki.ti.com/index.php/AM335x_PSP_WDT_Driver_User_Guide

Thanks for the link.

I know that I can control the watchdog (when enabled in linux) through /dev/watchdog. But I dont want the kernel to handle the watchdog, but control the watchdog directly with mmap and therefore disabled the watchdog in the linux menuconfig. However this is not possible because of the error I posted above. So I wonder if there is something special with the adress range at 0x44E35000 because I can modify regs in other ranges without problems.

I suggest you read through section 20.4 in the AM335X TRM Rev. K. For some accesses the WDT must be stopped/started by writing certain sequences.

Thanks again Biser.

I forgot to mention that I try to set the start sequence, but I get the error as soon as I access the WDT_WSPR register (the register to write the start/stop sequence).  

Could it be that the WDT is completely disabled in your case and needs to be initialized first?

The WDT gets initialized in the bootloader and is already active (with 60 seconds timeout) when linux starts. I also tried it with the watchdog enabled in linux, but I always get the same error as soon as I try to access a WD register through mmap. 

any other ideas anyone?

Hi James,

Thanks a lot!

enabling the clock  (0x44e0_04D4 = 0x2) resolved the problem!

I selected the PER PLL clock as  CLKSEL_WDT1_CLK because the RC osc seems to be very inaccurate or I misconfigured something (60 seconds wd timeout resulted in a reset of the am335x after 54 seconds). The PER PLL clock however works fine.

Just one more thing: The WD is already enabled (by the bootloader) which is good, however I'd like to decrease the timeout (from 60s to 10s) in my application. It looks like it's not possible to change the timeout without disabling the WD first, is that true? I'd like to have the WD always enabled.

Yes, you have to disable the WDT first. See section 20.4.3.9 in the AM335X TRM Rev. K.