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// This is a minimal 16550 UART driver for COM1, this is mainly going
// to be used for debugging since its really simple to setup.
// Fun fact: i was drunk when i wrote this
//
// see: https://wiki.osdev.org/Serial_Ports
const COM1: u16 = 0x3F8;
inline fn outb(port: u16, val: u8) void {
asm volatile ("outb %[val], %[port]"
:
: [val] "{al}" (val),
[port] "N{dx}" (port),
);
}
inline fn inb(port: u16) u8 {
return asm volatile ("inb %[port], %[result]"
: [result] "={al}" (-> u8),
: [port] "N{dx}" (port),
);
}
// 38400 buard
// 8 data bits
// no parity
// one stop bit
// FIFO on
// Idempotent so it should be relatively safe to call
// from the panic handler.
pub fn init() void {
outb(COM1 + 1, 0x00); // no interrupts
outb(COM1 + 3, 0x80); // DLAB on: the next two writes set the baud divisor
outb(COM1 + 0, 0x03); // divisor 3 -> 38400 baud (low byte)
outb(COM1 + 1, 0x00); // divisor high byte
outb(COM1 + 3, 0x03); // DLAB off, 8N1
outb(COM1 + 2, 0xC7); // enable + clear FIFOs, 14-byte trigger
outb(COM1 + 4, 0x0B); // RTS/DSR set
}
// COM1+5 (bit 5) = transmit holding register and
// spin until it's clear to send
fn putc(c: u8) void {
while (inb(COM1 + 5) & 0x20 == 0) {}
outb(COM1, c);
}
pub fn write(s: []const u8) void {
for (s) |c| putc(c);
}
// dump a u64 as decimal. handy for "usable: N MiB" type logging.
pub fn writeDec(value: u64) void {
if (value == 0) return putc('0');
var buf: [20]u8 = undefined;
var i: usize = buf.len;
var v = value;
while (v > 0) {
i -= 1;
buf[i] = '0' + @as(u8, @intCast(v % 10));
v /= 10;
}
write(buf[i..]);
}
// dump a u64 as 0x-prefixed 16-digit hex.
pub fn writeHex(value: u64) void {
const digits = "0123456789abcdef";
var buf: [18]u8 = undefined;
buf[0] = '0';
buf[1] = 'x';
var i: usize = 0;
while (i < 16) : (i += 1) {
const shift: u6 = @intCast((15 - i) * 4);
buf[2 + i] = digits[(value >> shift) & 0xF];
}
write(&buf);
}
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