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