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APIC timer calibration

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Now the APIC timer is calibrated against the PIT, and the interval for
timer_enable takes a number of microseconds instead of raw ticks and a
divisor.
This commit is contained in:
Justin C. Miller
2018-09-16 18:56:01 -07:00
parent 482b9f50fc
commit 5e6769036c
7 changed files with 126 additions and 47 deletions
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60
src/kernel/apic.cpp
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@@ -1,6 +1,7 @@
#include "kutil/assert.h"
#include "apic.h"
#include "interrupts.h"
#include "io.h"
#include "log.h"
#include "page_manager.h"
@@ -50,7 +51,46 @@ lapic::lapic(uint32_t *base, isr spurious) :
}
void
lapic::enable_timer(isr vector, uint8_t divisor, uint32_t count, bool repeat)
lapic::calibrate_timer()
{
interrupts_disable();
log::info(logs::apic, "Calibrating APIC timer...");
// Set up PIT sleep
uint8_t command = 0x30; // channel 0, loybyte/highbyte, mode 0
outb(0x43, command);
const uint32_t initial = -1u;
enable_timer_internal(isr::isrIgnore0, 1, initial, false);
const int iterations = 5;
for (int i=0; i<iterations; ++i) {
const uint16_t pit_33ms = 39375;
uint16_t pit_count = pit_33ms;
outb(0x40, pit_count & 0xff);
io_wait();
outb(0x40, (pit_count >> 8) & 0xff);
while (pit_count <= pit_33ms) {
outb(0x43, 0); // latch counter values
pit_count =
static_cast<uint16_t>(inb(0x40)) |
static_cast<uint16_t>(inb(0x40)) << 8;
}
}
uint32_t remain = stop_timer();
uint32_t ticks_total = initial - remain;
m_ticks_per_us = ticks_total / (iterations * 33000);
log::info(logs::apic, "APIC timer ticks %d times per nanosecond.", m_ticks_per_us);
interrupts_enable();
}
uint32_t
lapic::enable_timer_internal(isr vector, uint8_t divisor, uint32_t count, bool repeat)
{
uint32_t divbits = 0;
@@ -76,12 +116,28 @@ lapic::enable_timer(isr vector, uint8_t divisor, uint32_t count, bool repeat)
apic_write(m_base, 0x3e0, divbits);
reset_timer(count);
return count;
}
uint32_t
lapic::enable_timer(isr vector, uint64_t interval, bool repeat)
{
uint64_t ticks = interval * m_ticks_per_us;
int divisor = 1;
while (ticks > -1u) {
ticks /= 2;
divisor *= 2;
}
log::debug(logs::apic, "Enabling APIC timer count %ld, divisor %d.", ticks, divisor);
return enable_timer_internal(vector, divisor, static_cast<uint32_t>(ticks), repeat);
}
uint32_t
lapic::reset_timer(uint32_t count)
{
uint32_t remaining = apic_read(m_base, 0x380);
uint32_t remaining = apic_read(m_base, 0x390);
apic_write(m_base, 0x380, count);
return remaining;
}