2 * ----------------------------------------------------------------------------
3 * "THE BEER-WARE LICENSE" (Revision 42):
4 * <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
5 * can do whatever you want with this stuff. If we meet some day, and you think
6 * this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
7 * ----------------------------------------------------------------------------
9 * Just when we thought life were beautiful, reality pops its grim face over
12 * ] 20. ACPI Timer Errata
14 * ] Problem: The power management timer may return improper result when
15 * ] read. Although the timer value settles properly after incrementing,
16 * ] while incrementing there is a 3nS window every 69.8nS where the
17 * ] timer value is indeterminate (a 4.2% chance that the data will be
18 * ] incorrect when read). As a result, the ACPI free running count up
19 * ] timer specification is violated due to erroneous reads. Implication:
20 * ] System hangs due to the "inaccuracy" of the timer when used by
21 * ] software for time critical events and delays.
23 * ] Workaround: Read the register twice and compare.
24 * ] Status: This will not be fixed in the PIIX4 or PIIX4E.
26 * The counter is in other words not latched to the PCI bus clock when
27 * read. Notice the workaround isn't: We need to read until we have
28 * three monotonic samples and then use the middle one, otherwise we are
29 * not protected against the fact that the bits can be wrong in two
30 * directions. If we only cared about monosity two reads would be enough.
32 * $FreeBSD: src/sys/i386/i386/mp_clock.c,v 1.4.2.2 2000/09/30 02:49:32 ps Exp $
35 #include <sys/param.h>
36 #include <sys/systm.h>
38 #include <sys/kernel.h>
39 #include <sys/sysctl.h>
44 #include <bus/pci/pcivar.h>
46 static unsigned piix_get_timecount(struct timecounter *tc);
48 static u_int32_t piix_timecounter_address;
49 static u_int piix_freq = 14318182/4;
51 static struct timecounter piix_timecounter = {
59 SYSCTL_OPAQUE(_debug, OID_AUTO, piix_timecounter, CTLFLAG_RD,
60 &piix_timecounter, sizeof(piix_timecounter), "S,timecounter", "");
63 sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
68 if (piix_timecounter.tc_frequency == 0)
71 error = sysctl_handle_int(oidp, &freq, 0, req);
72 if (error == 0 && req->newptr != NULL) {
74 piix_timecounter.tc_frequency = piix_freq;
75 update_timecounter(&piix_timecounter);
80 SYSCTL_PROC(_machdep, OID_AUTO, piix_freq, CTLTYPE_INT | CTLFLAG_RW,
81 0, sizeof(u_int), sysctl_machdep_piix_freq, "I", "");
84 piix_get_timecount(struct timecounter *tc)
88 u2 = inl(piix_timecounter_address);
89 u3 = inl(piix_timecounter_address);
93 u3 = inl(piix_timecounter_address);
94 } while (u1 > u2 || u2 > u3);
99 piix_probe (device_t dev)
103 switch (pci_get_devid(dev)) {
105 d = pci_read_config(dev, 0x4, 2);
107 return 0; /* IO space not mapped */
108 d = pci_read_config(dev, 0x40, 4);
109 piix_timecounter_address = (d & 0xffc0) + 8;
110 piix_timecounter.tc_frequency = piix_freq;
111 init_timecounter(&piix_timecounter);
118 piix_attach (device_t dev)
124 static device_method_t piix_methods[] = {
125 /* Device interface */
126 DEVMETHOD(device_probe, piix_probe),
127 DEVMETHOD(device_attach, piix_attach),
131 static driver_t piix_driver = {
137 static devclass_t piix_devclass;
139 DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, NULL, NULL);