On 4/1/10, Artyom Tarasenko <atar4q...@googlemail.com> wrote:
> 2010/4/1 Blue Swirl <blauwir...@gmail.com>:
> > Which list?
>
> This mailing list?
>
>
> > On 4/1/10, Artyom Tarasenko <atar4q...@googlemail.com> wrote:
> >> and looks wrong or incomplete to me:
> >>
> >> >According to Sun4M System Architecture Manual chapter 5.3.2, a limit
> >> >of 0 will not generate interrupts.
> >>
> >> This is indeed correct, but the chapter 5.3.2 also explains why:
> >>
> >> "Setting the limit register to 0 allows the counter to free run. Since
> the
> >> timer always resets to a value of 500 nS after reaching maximum count,
> >> there is no match and no interrupts are generated."
> >>
> >> The part about 500 nS (0x00000200 in the counter register) and
> >> no match seems to be not addressed.
> >
> > The 500ns offset part could be addressed by making the timer period
> > shorter by 1 tick. I doubt such a change would have any visible
> > difference with QEMU, except that tick count of 0 should never appear
> > in the counter but it may now.
>
>
> as well as all the other values between 0 and 0x200. But it's less
> important I guess.
>
>
> > For the no match part, t->reached should not be set if t->limit == 0.
I think this patch would do what is expected.
From 7ef9679874d24f3062bf64525d9dd13d45dc2f27 Mon Sep 17 00:00:00 2001
From: Blue Swirl <blauwir...@gmail.com>
Date: Fri, 2 Apr 2010 15:54:26 +0000
Subject: [PATCH] sparc32: improve timer implementation
Timer with zero period (free-run) will never match.
Timer counting starts with tick value of 0x200, not from 0,
so the period must calculated from one tick less than the limit.
Signed-off-by: Blue Swirl <blauwir...@gmail.com>
---
hw/slavio_timer.c | 9 ++++++---
1 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/hw/slavio_timer.c b/hw/slavio_timer.c
index ef36fe4..d787553 100644
--- a/hw/slavio_timer.c
+++ b/hw/slavio_timer.c
@@ -88,8 +88,8 @@ typedef struct TimerContext {
#define TIMER_MAX_COUNT32 0x7ffffe00ULL
#define TIMER_REACHED 0x80000000
#define TIMER_PERIOD 500ULL // 500ns
-#define LIMIT_TO_PERIODS(l) ((l) >> 9)
-#define PERIODS_TO_LIMIT(l) ((l) << 9)
+#define LIMIT_TO_PERIODS(l) (((l) >> 9) - 1)
+#define PERIODS_TO_LIMIT(l) (((l) + 1) << 9)
static int slavio_timer_is_user(TimerContext *tc)
{
@@ -127,7 +127,10 @@ static void slavio_timer_irq(void *opaque)
slavio_timer_get_out(t);
DPRINTF("callback: count %x%08x\n", t->counthigh, t->count);
- t->reached = TIMER_REACHED;
+ /* if limit is 0 (free-run), there will be no match */
+ if (t->limit != 0) {
+ t->reached = TIMER_REACHED;
+ }
/* there is no interrupt if user timer or free-run */
if (!slavio_timer_is_user(tc) && t->limit != 0) {
qemu_irq_raise(t->irq);
--
1.5.6.5
