Le 23/01/2011 20:35, Wolfgang Denk a écrit :
At the moment I would suggest to change the existing interface like that:
Drop the set_timer() function.
Change get_timer() to take no argument, i. e.:
unsigned long get_timer(void);
get_timer() returns a monotonous upward counting time stamp with a resolution of milliseconds. After reaching ULONG_MAX the timer wraps around to 0.
The get_timer() implementation may be interrupt based and is only available after relocation.
Provide a fast, low-level, system dependent timer function
unsigned long long get_ticks(void);
get_ticks() returns a monotonous upward counting time stamp with a system-specific resolution. No assumptions should be made about the resolution. After reaching ULLONG_MAX the timer wraps around to 0.
It is mandatory that get_ticks() is available before relocation.
Provide a set of utility functions:
-> void wait_ticks(unsigned long ticks);
Delay execution for "ticks" ticks.
-> unsigned long usec2ticks(unsigned long usec);
Convert microseconds into ticks; intended for SHORT delays only (maximum depending on system clock, usually below 1 second).
-> void __udelay(unsigned long usec);
Delay execution for "usec" microseconds; intended for SHORT delays only (maximum depending on system clock, usually below 1 second). If all architectures followed the above suggestion, we could move the PPC implementation to common code:
void __udelay(unsigned long usec) { ulong ticks = usec2ticks(usec); wait_ticks(ticks); }
__udelay() can reliably be used before relocation.
-> void udelay(unsigned long usec)
Similar to __udelay() with the additional functionality to trigger the watchdog timer for long delays.
that will not be possible on most hardware without complicated code. We have discussed that long ago...
I am aware of this.
Well, you could try to understand: tick=the "at hardware speed running" timer, if that's incrementing too fast for 32 bit "timeout" vars for reasonable timeouts (up to a minute?),
See above. For short, high resolution timeouts you can use get_ticks() and friends. For long delays you can use get_timer().
Note that "reasonable timeouts (up to a minute?)" are only very infrequently needed, and don't need the high resolution of get_ticks(), so these would naturally be implemented on the base of get_timer().
We have been using this implementation for more than a decade on PowerPC. The only thing you need is a monotonous upward counting 64 bit "time base" counter where you can read the system ticks from.
Best regards,
Wolfgang Denk
This proposal covers what I was thinking of (oubviously I had not looked into PPC implementations) and the few differences with my proposal are not worth fighting over, so overall I am fine with the above.
Let us hear from others now, and if we reach an agreement, then we'll start discussing implementation.
Amicalement,