1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * Machine specific calibrate_tsc() for generic.
4 * Split out from timer_tsc.c by Osamu Tomita <tomita@cinet.co.jp>
5 */
6 /* ------ Calibrate the TSC -------
7 * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
8 * Too much 64-bit arithmetic here to do this cleanly in C, and for
9 * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
10 * output busy loop as low as possible. We avoid reading the CTC registers
11 * directly because of the awkward 8-bit access mechanism of the 82C54
12 * device.
13 */
14 #ifndef _ASM_X86_MACH_DEFAULT_MACH_TIMER_H
15 #define _ASM_X86_MACH_DEFAULT_MACH_TIMER_H
16
17 #define CALIBRATE_TIME_MSEC 30 /* 30 msecs */
18 #define CALIBRATE_LATCH \
19 ((PIT_TICK_RATE * CALIBRATE_TIME_MSEC + 1000/2)/1000)
20
21 static inline void mach_prepare_counter(void)
22 {
23 /* Set the Gate high, disable speaker */
24 outb((inb(0x61) & ~0x02) | 0x01, 0x61);
25
26 /*
27 * Now let's take care of CTC channel 2
28 *
29 * Set the Gate high, program CTC channel 2 for mode 0,
30 * (interrupt on terminal count mode), binary count,
31 * load 5 * LATCH count, (LSB and MSB) to begin countdown.
32 *
33 * Some devices need a delay here.
34 */
35 outb(0xb0, 0x43); /* binary, mode 0, LSB/MSB, Ch 2 */
36 outb_p(CALIBRATE_LATCH & 0xff, 0x42); /* LSB of count */
37 outb_p(CALIBRATE_LATCH >> 8, 0x42); /* MSB of count */
38 }
39
40 static inline void mach_countup(unsigned long *count_p)
41 {
42 unsigned long count = 0;
43 do {
44 count++;
45 } while ((inb_p(0x61) & 0x20) == 0);
46 *count_p = count;
47 }
48
49 #endif /* _ASM_X86_MACH_DEFAULT_MACH_TIMER_H */
50
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