[OpenBIOS] r407 - openbios-devel/arch/ppc/qemu
svn at openbios.org
svn at openbios.org
Thu Jan 15 00:25:41 CET 2009
Date: 2009-01-15 00:25:41 +0100 (Thu, 15 Jan 2009)
New Revision: 407
PowerPC: Fix milliseconds prom call
The current implementation of the milliseconds prom call on PowerPC is
- The timer frequency returned by get_timer_freq() does not correspond
to the timer which is read.
- The dividend and the divisor of the division are swapped
- If called very often, this function is not precise
- Depending on the timer frequency and of the frequency of the calls,
the variable overflow after a few dozen of seconds.
Please find in this patch a totally new implementation. This fixes the
problem observed with the quik when a timeout is defined.
The timer frequency is defined using #define, I wonder if there is a
better place to put it.
It reads both low and high part of the timer to make sure there is no
overflow. It also removes the function that returns 0 on the first call
as this is not needed according to IEEE 1275-1994. Finally it computes
the real value of the timer each time, instead of adding a small value
to a variable at each function calls, in order to get a correct
precision if this method is call very often.
--- openbios-devel/arch/ppc/qemu/methods.c 2009-01-13 20:24:52 UTC (rev 406)
+++ openbios-devel/arch/ppc/qemu/methods.c 2009-01-14 23:25:41 UTC (rev 407)
@@ -122,19 +122,28 @@
/* ( -- ms ) */
+#define TIMER_FREQUENCY 16600000ULL
ciface_milliseconds( ulong args, ulong ret )
- extern unsigned long get_timer_freq(void);
- static ulong mticks=0, usecs=0;
- ulong t;
+ ulong tbu, tbl, temp;
+ ullong ticks, msecs;
- asm volatile("mftb %0" : "=r" (t) : );
- if( mticks )
- usecs += get_timer_freq() / 1000000 * ( t-mticks );
- mticks = t;
+ asm volatile(
+ "mftbu %2\n"
+ "mftb %0\n"
+ "mftbu %1\n"
+ "cmpw %2,%1\n"
+ "bne 1b\n"
+ : "=r"(tbl), "=r"(tbu), "=r"(temp)
+ : "cc");
- PUSH( usecs/1000 );
+ ticks = (((ullong)tbu) << 32) | (ullong)tbl;
+ msecs = (1000 * ticks) / TIMER_FREQUENCY;
+ PUSH( msecs );
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