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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Machine specific calibrate_tsc() for generic.
* Split out from timer_tsc.c by Osamu Tomita <[email protected]>
*/
/* ------ Calibrate the TSC -------
* Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
* 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.
*/
#ifndef _ASM_X86_MACH_DEFAULT_MACH_TIMER_H
#define _ASM_X86_MACH_DEFAULT_MACH_TIMER_H
#define CALIBRATE_TIME_MSEC 30 /* 30 msecs */
#define CALIBRATE_LATCH \
((PIT_TICK_RATE * CALIBRATE_TIME_MSEC + 1000/2)/1000)
static inline void mach_prepare_counter(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.
*
* Some devices need a delay here.
*/
outb(0xb0, 0x43); /* binary, mode 0, LSB/MSB, Ch 2 */
outb_p(CALIBRATE_LATCH & 0xff, 0x42); /* LSB of count */
outb_p(CALIBRATE_LATCH >> 8, 0x42); /* MSB of count */
}
static inline void mach_countup(unsigned long *count_p)
{
unsigned long count = 0;
do {
count++;
} while ((inb_p(0x61) & 0x20) == 0);
*count_p = count;
}
#endif /* _ASM_X86_MACH_DEFAULT_MACH_TIMER_H */
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