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// x86 programmable interrupt timer
// TODO there should be an machine level timer abstraction
use crate::machine::device_io::IOPort;
pub struct PIT {}
impl PIT {
const CTRL_PORT: IOPort = IOPort::new(0x43);
const DATA_PORT: IOPort = IOPort::new(0x40);
const PIT_BASE_FREQ: u64 = 1193182;
// 1193182 Hz is roughly 838 ns
const PIT_BASE_NS: u64 = 838;
// max is around 54918 us (54 ms)
pub fn set_interval(us: u64) -> u64 {
let mut divider = (us * 1000 + Self::PIT_BASE_NS / 2) / Self::PIT_BASE_NS;
if divider == 0 {
panic!("how on earth can you make a zero divider?")
}
if divider >= 65535 {
divider = 65535;
}
// TODO 65536 actually translates to 0
Self::CTRL_PORT.outb(0x34);
Self::DATA_PORT.outb((divider & 0xff) as u8);
Self::DATA_PORT.outb(((divider & 0xff00) >> 8) as u8);
return divider * Self::PIT_BASE_NS;
}
}
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