From 432516586e7f646aa2a8ac0cbdf8e80ac44f97d0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ky=C3=B6sti=20M=C3=A4lkki?= Date: Thu, 31 Oct 2019 13:25:23 +0200 Subject: cpu/x86: Move calibrate_tsc_with_pit() to drivers/pc80 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Change-Id: Ia8d8dc23ee0b51d62c83f5ba640b3a9aea4e744b Signed-off-by: Kyösti Mälkki Reviewed-on: https://review.coreboot.org/c/coreboot/+/36507 Tested-by: build bot (Jenkins) Reviewed-by: Marshall Dawson --- src/drivers/pc80/pc/i8254.c | 76 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 76 insertions(+) (limited to 'src/drivers/pc80/pc/i8254.c') diff --git a/src/drivers/pc80/pc/i8254.c b/src/drivers/pc80/pc/i8254.c index 53d880cc79..8e15d4ded1 100644 --- a/src/drivers/pc80/pc/i8254.c +++ b/src/drivers/pc80/pc/i8254.c @@ -12,6 +12,8 @@ */ #include +#include +#include #include /* Initialize i8254 timers */ @@ -46,3 +48,77 @@ void udelay(int usecs) ; } #endif + +#define CLOCK_TICK_RATE 1193180U /* Underlying HZ */ + +/* ------ Calibrate the TSC ------- + * Too much 64-bit arithmetic here to do this cleanly in C, and for + * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2) + * output busy loop as low as possible. We avoid reading the CTC registers + * directly because of the awkward 8-bit access mechanism of the 82C54 + * device. + */ + +#define CALIBRATE_INTERVAL ((2*CLOCK_TICK_RATE)/1000) /* 2ms */ +#define CALIBRATE_DIVISOR (2*1000) /* 2ms / 2000 == 1usec */ + +unsigned long calibrate_tsc_with_pit(void) +{ + /* Set the Gate high, disable speaker */ + outb((inb(0x61) & ~0x02) | 0x01, 0x61); + + /* + * Now let's take care of CTC channel 2 + * + * Set the Gate high, program CTC channel 2 for mode 0, + * (interrupt on terminal count mode), binary count, + * load 5 * LATCH count, (LSB and MSB) to begin countdown. + */ + outb(0xb0, 0x43); /* binary, mode 0, LSB/MSB, Ch 2 */ + + outb(CALIBRATE_INTERVAL & 0xff, 0x42); /* LSB of count */ + outb(CALIBRATE_INTERVAL >> 8, 0x42); /* MSB of count */ + + { + tsc_t start; + tsc_t end; + unsigned long count; + + start = rdtsc(); + count = 0; + do { + count++; + } while ((inb(0x61) & 0x20) == 0); + end = rdtsc(); + + /* Error: ECTCNEVERSET */ + if (count <= 1) + goto bad_ctc; + + /* 64-bit subtract - gcc just messes up with long longs */ + __asm__("subl %2,%0\n\t" + "sbbl %3,%1" + : "=a" (end.lo), "=d" (end.hi) + : "g" (start.lo), "g" (start.hi), + "0" (end.lo), "1" (end.hi)); + + /* Error: ECPUTOOFAST */ + if (end.hi) + goto bad_ctc; + + + /* Error: ECPUTOOSLOW */ + if (end.lo <= CALIBRATE_DIVISOR) + goto bad_ctc; + + return DIV_ROUND_UP(end.lo, CALIBRATE_DIVISOR); + } + + /* + * The CTC wasn't reliable: we got a hit on the very first read, + * or the CPU was so fast/slow that the quotient wouldn't fit in + * 32 bits.. + */ +bad_ctc: + return 0; +} -- cgit v1.2.3