Ok, here is a patch that executes a brute-force solution to the
asynchronous counter problem.
Basically it figures out a mask and then the timer code loops until two
masked reads yield the same value, guarenteeing that we haven't caught
the timer during a carry.
On my system, the mask I got was: 0xFFFFFFFC which means I lost only 2
bits of accuracy in order to be able to retrieve accurate counter values.
This gives my particular box an approximately 1uS accuracy.
I think this may be the only safe way to do it. It looks like it is
possible to catch the ripple and/or fast-carry on *any* bit, with the
statistical chance of it occuring on higher bits dropping by 2x per bit.
My proposed (tested) patch is below. Mike?
acpi_timer0: <32-bit timer at 3.579545MHz mask fffffffc> port 0x808-0x80b on acpi0
-Matt
Index: acpi_timer.c
===================================================================
RCS file: /home/ncvs/src/sys/dev/acpica/acpi_timer.c,v
retrieving revision 1.11
diff -u -r1.11 acpi_timer.c
--- acpi_timer.c 8 Jan 2002 06:45:56 -0000 1.11
+++ acpi_timer.c 17 Feb 2002 23:26:29 -0000
@@ -56,6 +56,7 @@
MODULE_NAME("TIMER")
static device_t acpi_timer_dev;
+static u_int32_t acpi_timer_mask;
struct resource *acpi_timer_reg;
#define TIMER_READ bus_space_read_4(rman_get_bustag(acpi_timer_reg), \
rman_get_bushandle(acpi_timer_reg), \
@@ -113,7 +114,7 @@
acpi_timer_identify(driver_t *driver, device_t parent)
{
device_t dev;
- char desc[40];
+ char desc[48];
int rid;
FUNCTION_TRACE(__func__);
@@ -138,14 +139,32 @@
if (getenv("debug.acpi.timer_test") != NULL)
acpi_timer_test();
- acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount;
+ acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount_safe;
acpi_timer_timecounter.tc_frequency = acpi_timer_frequency;
tc_init(&acpi_timer_timecounter);
- sprintf(desc, "%d-bit timer at 3.579545MHz", AcpiGbl_FADT->TmrValExt ? 32 : 24);
+ for (acpi_timer_mask = 0xFFFFFFFF; acpi_timer_mask; acpi_timer_mask <<= 1) {
+ u_int32_t u1;
+ u_int32_t u2;
+ int count = 10;
+
+ u1 = TIMER_READ;
+ u2 = TIMER_READ;
+ while (count && ((u1 ^ u2) & acpi_timer_mask)) {
+ u1 = u2;
+ u2 = TIMER_READ;
+ --count;
+ }
+ if (count)
+ break;
+ }
+ acpi_timer_mask <<= 1;
+
+ sprintf(desc, "%d-bit timer at 3.579545MHz mask %08x",
+ (AcpiGbl_FADT->TmrValExt ? 32 : 24), acpi_timer_mask);
device_set_desc_copy(dev, desc);
-#if 0
+#if 0
{
u_int64_t first;
@@ -192,16 +211,22 @@
static unsigned
acpi_timer_get_timecount_safe(struct timecounter *tc)
{
- unsigned u1, u2, u3;
+ u_int32_t u1;
+ u_int32_t u2;
+ u1 = TIMER_READ;
u2 = TIMER_READ;
- u3 = TIMER_READ;
- do {
+ while ((u1 ^ u2) & acpi_timer_mask) {
u1 = u2;
- u2 = u3;
- u3 = TIMER_READ;
- } while (u1 > u2 || u2 > u3);
- return (u2);
+ u2 = TIMER_READ;
+ }
+#if 0 /* DEBUGGING */
+ if (u2 < u1) {
+ u_int32_t u3 = TIMER_READ;
+ printf("ACPI TIMER LSB MISREAD %08x %08x %08x\n", u1, u2, u3);
+ }
+#endif
+ return(u2 & acpi_timer_mask);
}
/*
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