blocking serial messages

1 files changed, 55 insertions, 0 deletions

diff --git a/src/mini_uart.zig b/src/mini_uart.zig
new file mode 100644
index 0000000..265268d
--- /dev/null
+++ b/src/mini_uart.zig
@@ -0,0 +1,55 @@
+const std = @import("std");
+
+const board = @import("board.zig");
+const AUX_BASE = board.AUX_BASE;
+const AUX_ENABLE = board.AUX_ENABLE;
+
+const gpio = @import("gpio.zig");
+const mmio = @import("mmio.zig");
+
+const IO = AUX_BASE + 0x40;
+const IER = AUX_BASE + 0x44;
+const IIR = AUX_BASE + 0x48;
+const LCR = AUX_BASE + 0x4c;
+const MCR = AUX_BASE + 0x50;
+const LSR = AUX_BASE + 0x54;
+const MSR = AUX_BASE + 0x58;
+const SCRATCH = AUX_BASE + 0x5c;
+const CNTL = AUX_BASE + 0x60;
+const STAT = AUX_BASE + 0x64;
+const BAUD = AUX_BASE + 0x68;
+
+pub fn enable() void {
+    board.enableAux(.mini_uart);
+
+    gpio.setPull(14, .none);
+    gpio.setFunction(14, .alt5);
+
+    gpio.setPull(15, .none);
+    gpio.setFunction(15, .alt5);
+
+    mmio.write(IER, 0); // disable interrupts
+    mmio.write(IIR, 6); // clear FIFOs
+    mmio.write(LCR, 3); // 8 bit mode
+    mmio.write(BAUD, baudRegVal(115200));
+
+    mmio.write(CNTL, 0x3);
+}
+
+fn baudRegVal(baud: comptime_int) comptime_int {
+    return 500000000 / (baud * 8) - 1;
+}
+
+fn writeByte(b: u8) void {
+    while ((mmio.read(LSR) & 0x10) != 0) {}
+    mmio.write(IO, b);
+}
+
+pub fn writeString(str: []const u8) void {
+    for (str) |b| {
+        if (b == '\n') {
+            writeByte('\r');
+        }
+        writeByte(b);
+    }
+}