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/* SPDX-License-Identifier: GPL-2.0-only */
#include <arch/io.h>
#include <commonlib/helpers.h>
#include <cpu/x86/tsc.h>
#include <pc80/i8254.h>
/* Initialize i8254 timers */
void setup_i8254(void)
{
/* Timer 0 (taken from biosemu) */
outb(TIMER0_SEL | WORD_ACCESS | MODE3 | BINARY_COUNT, TIMER_MODE_PORT);
outb(0x00, TIMER0_PORT);
outb(0x00, TIMER0_PORT);
/* Timer 1 */
outb(TIMER1_SEL | LOBYTE_ACCESS | MODE3 | BINARY_COUNT,
TIMER_MODE_PORT);
outb(0x12, TIMER1_PORT);
}
#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;
}
#if CONFIG(UNKNOWN_TSC_RATE)
static u32 timer_tsc;
unsigned long tsc_freq_mhz(void)
{
if (timer_tsc > 0)
return timer_tsc;
timer_tsc = calibrate_tsc_with_pit();
/* Set some semi-ridiculous rate if approximation fails. */
if (timer_tsc == 0)
timer_tsc = 5000;
return timer_tsc;
}
#endif
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