Hi Simon,
On Thu, Jun 16, 2011 at 3:53 PM, Simon Glass sjg@chromium.org wrote:
Hi Graeme,
On Wed, Jun 15, 2011 at 4:09 PM, Graeme Russ graeme.russ@gmail.com wrote: [snip]
BTW should the deltas return a signed value?
No - times are unsigned utilising the entire range of the u32 so (to - from) will always returned the unsigned delta, even if there is a wrap between them. I cannot imagine we would ever need to measure time backward anyway.
Can you please explain this again in different words as I don't follow. The difference between two unsigned times may be +ve or -ve, surely. For example, say:
now = 100 event_time = 200
then the delta is currently -100. Some people might loop until the delta is >= 0. This is like setting a future time and waiting for it to happen. If the delta is unsigned then this won't work.
start = 0xffffff00 now = 0x00000010
So there was a timer wrap between 'start' and 'now'
delta = now - start = 0x110
Remember that the new timer API does not rely on the tick counter (and therefore the ms/us timers) to start at zero - It must be allowed to wrap without causing timer glitches at any arbitray time
Regards,
Graeme