93 lines
2.4 KiB
C
93 lines
2.4 KiB
C
/* Some utility functions around the free running clock on ARM. The clock is
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* 32-bits wide, but we provide 64-bit wrapper functions to make it look
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* similar to the read_tsc functions. On hardware we could actually make use
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* of the timer overflow counter, but emulator doesn't emulate it. */
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#include <minix/minlib.h>
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#include <minix/sysutil.h>
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#include <minix/type.h>
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#include <sys/errno.h>
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#include <sys/types.h>
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#include <assert.h>
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#define MICROHZ 1000000ULL /* number of micros per second */
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#define MICROSPERTICK(h) (MICROHZ/(h)) /* number of micros per HZ tick */
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static u64_t Hz;
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extern struct minix_kerninfo *_minix_kerninfo;
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int
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micro_delay(u32_t micros)
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{
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u64_t start, delta, delta_end;
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Hz = sys_hz();
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/* Start of delay. */
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read_frclock_64(&start);
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assert(_minix_kerninfo->minix_arm_frclock_hz);
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delta_end = (_minix_kerninfo->minix_arm_frclock_hz * micros) / MICROHZ;
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/* If we have to wait for at least one HZ tick, use the regular
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* tickdelay first. Round downwards on purpose, so the average
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* half-tick we wait short (depending on where in the current tick
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* we call tickdelay). We can correct for both overhead of tickdelay
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* itself and the short wait in the busywait later.
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*/
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if (micros >= MICROSPERTICK(Hz))
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tickdelay(micros*Hz/MICROHZ);
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/* Wait (the rest) of the delay time using busywait. */
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do {
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read_frclock_64(&delta);
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} while (delta_frclock_64(start, delta) < delta_end);
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return 0;
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}
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u32_t frclock_64_to_micros(u64_t tsc)
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{
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return (u32_t) (tsc / (_minix_kerninfo->minix_arm_frclock_hz / MICROHZ));
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}
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void
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read_frclock(u32_t *frclk)
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{
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assert(frclk);
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assert(_minix_kerninfo->minix_frclock_tcrr);
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assert(_minix_kerninfo->minix_arm_frclock_hz);
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*frclk = *(volatile u32_t *)((u8_t *) _minix_kerninfo->minix_frclock_tcrr);
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}
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u32_t
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delta_frclock(u32_t base, u32_t cur)
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{
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u32_t delta;
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if (cur < base) {
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/* We have wrapped around, so delta is base to wrapping point
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* plus starting point (0) to cur. This supports wrapping once
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* only. */
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delta = (UINT_MAX - base) + cur;
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} else {
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delta = cur - base;
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}
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return delta;
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}
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void
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read_frclock_64(u64_t *frclk)
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{
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read_frclock((u32_t *) frclk);
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}
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u64_t
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delta_frclock_64(u64_t base, u64_t cur)
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{
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return (u64_t) delta_frclock((u32_t) base, (u32_t) cur);
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}
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