46 lines
1.3 KiB
C
46 lines
1.3 KiB
C
/* pit.c — PIT ch0 单发定时（LAPIC timer 校准用）
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*
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* 只用 mode 0（terminal count）：单发、无周期中断、不注册 IRQ handler。
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* 禁用 mode 3 —— B7 定论：PIT mode3 方波经 IOAPIC 边沿路由会双触发 (~200Hz)。
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*/
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#include <utsm/pit.h>
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extern void outb(u16 port, u8 value);
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extern u8 inb(u16 port);
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#define PIT_CH0_DATA 0x40
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#define PIT_CMD 0x43
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#define PIT_BASE_HZ 1193182ULL
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void pit_oneshot_ms(u32 ms) {
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u64 div = (PIT_BASE_HZ * (u64)ms) / 1000ULL;
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if (div == 0) div = 1;
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if (div > 65535) div = 65535;
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/* ch0 | lo/hi | mode0 (terminal count) | binary */
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outb(PIT_CMD, 0x30);
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outb(PIT_CH0_DATA, (u8)(div & 0xFF));
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outb(PIT_CH0_DATA, (u8)((div >> 8) & 0xFF));
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}
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u16 pit_latch_count(void) {
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outb(PIT_CMD, 0x00); /* ch0 latch 计数（读前锁存） */
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u16 lo = inb(PIT_CH0_DATA);
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u16 hi = inb(PIT_CH0_DATA);
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return (u16)(lo | (hi << 8));
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}
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int pit_oneshot_expired(void) {
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u16 c1 = pit_latch_count();
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u16 c2 = pit_latch_count();
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/* mode0 计到 0 后回绕继续递减：cur 回升即视为到期 */
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return c2 >= c1;
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}
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void pit_quiet(void) {
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/* ch0 mode0、计数 0：terminal count 立即到期，无后续输出/中断 */
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outb(PIT_CMD, 0x30);
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outb(PIT_CH0_DATA, 0x00);
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outb(PIT_CH0_DATA, 0x00);
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}
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