80 lines
2.2 KiB
Zig
80 lines
2.2 KiB
Zig
const arch = @import("arch.zig").internals;
|
|
|
|
// The LCR is the line control register
|
|
const LCR = 3;
|
|
// Maximum baudrate
|
|
const BAUD_MAX = 115200;
|
|
// 8 bits per serial character
|
|
const CHAR_LEN = 8;
|
|
// One stop bit per transmission
|
|
const SINGLE_STOP_BIT = true;
|
|
// No parity bit
|
|
const PARITY_BIT = false;
|
|
|
|
pub const DEFAULT_BAUDRATE = 38400;
|
|
|
|
const SerialError = error {
|
|
InvalidBaud
|
|
};
|
|
|
|
pub const Port = enum(u16) {
|
|
COM1 = 0x3F8,
|
|
COM2 = 0x2F8,
|
|
COM3 = 0x3E8,
|
|
COM4 = 0x2E8
|
|
};
|
|
|
|
// Compute a value that encodes the serial properties
|
|
// This is fed into the LCR (line control register)
|
|
fn lcrValue(char_len: u8, comptime stop_bit: bool, comptime parity_bit: bool, msb: u8) u8 {
|
|
var val = char_len & 0x3;
|
|
val |= (if (stop_bit) 0 else 1) << 2;
|
|
val |= (if (parity_bit) 1 else 0) << 3;
|
|
val |= (msb & 0x1) << 7;
|
|
return val;
|
|
}
|
|
|
|
fn baudDivisor(baud: u32) SerialError!u16 {
|
|
if (baud > BAUD_MAX or baud <= 0) return SerialError.InvalidBaud;
|
|
return @intCast(u16, BAUD_MAX / baud);
|
|
}
|
|
|
|
fn transmitIsEmpty(port: Port) bool {
|
|
return arch.inb(@enumToInt(port) + 5) & 0x20 > 0;
|
|
}
|
|
|
|
///
|
|
/// Initialise a serial port to a certain baudrate
|
|
///
|
|
/// Arguments
|
|
/// IN baud: u32 - The baudrate to use. Cannot be more than MAX_BAUDRATE
|
|
/// IN port: Port - The port to initialise
|
|
///
|
|
/// Throws a SerialError if the baudrate is invalid
|
|
///
|
|
pub fn init(baud: u32, port: Port) SerialError!void {
|
|
// The baudrate is sent as a divisor of the max baud rate
|
|
const divisor: u16 = try baudDivisor(baud);
|
|
const port_int = @enumToInt(port);
|
|
// Send a byte to start setting the baudrate
|
|
arch.outb(port_int + LCR, lcrValue(0, false, false, 1));
|
|
// Send the divisor's lsb
|
|
arch.outb(port_int, @truncate(u8, divisor));
|
|
// Send the divisor's msb
|
|
arch.outb(port_int + 1, @truncate(u8, divisor >> 8));
|
|
// Send the properties to use
|
|
arch.outb(port_int + LCR, lcrValue(CHAR_LEN, SINGLE_STOP_BIT, PARITY_BIT, 0));
|
|
// Stop initialisation
|
|
arch.outb(port_int + 1, 0);
|
|
}
|
|
|
|
pub fn write(char: u8, port: Port) void {
|
|
while (!transmitIsEmpty(port)) { arch.halt(); }
|
|
arch.outb(@enumToInt(port), char);
|
|
}
|
|
|
|
pub fn writeString(str: []const u8, port: Port) void {
|
|
for (str) |char| {
|
|
write(char, port);
|
|
}
|
|
}
|