The 05/02/2019 22:55, Alexandre Belloni wrote: > > * I don't think pcf2123_read_offset is working correctly. In the case of > > a coarse offset the value is not being sign extended. So a negative > > offset read will not be correct if the coarse bit is set (result would > > be a positive number being returned if this is true). I need to look > > into this some more. The fix would be to sign extend first, then if > > coarse bit is set multiply the result by 2. > > > > As the comment says, it is properly extended because after shifting, > bits [6:0] become bit [7:1]. > But what about this: # echo 2170 > /sys/class/rtc/rtc0/offset # cat /sys/class/rtc/rtc0/offset 2170 # echo -2170 > /sys/class/rtc/rtc0/offset # cat /sys/class/rtc/rtc0/offset 0 # echo 4340 > /sys/class/rtc/rtc0/offset # cat /sys/class/rtc/rtc0/offset 4340 # echo -4340 > /sys/class/rtc/rtc0/offset # cat /sys/class/rtc/rtc0/offset -2170 Negative offset reads seem to be off by a factor of 2. -- Dylan
