From 40575cafe477df2ed3779789174a13eae5da187e Mon Sep 17 00:00:00 2001
From: Josh Rahm <joshuarahm@gmail.com>
Date: Wed, 18 Dec 2024 00:30:51 -0700
Subject: Initial commit for programming an arduino in Zig.

This is a simple collatz blinker program.
---
 blink.zig | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 build.zig | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 init.zig  | 27 ++++++++++++++++++++++
 linker.ld | 33 +++++++++++++++++++++++++++
 4 files changed, 204 insertions(+)
 create mode 100644 blink.zig
 create mode 100644 build.zig
 create mode 100644 init.zig
 create mode 100644 linker.ld

diff --git a/blink.zig b/blink.zig
new file mode 100644
index 0000000..4444427
--- /dev/null
+++ b/blink.zig
@@ -0,0 +1,66 @@
+const std = @import("std");
+
+const DDRB = @as(*volatile u8, @ptrFromInt(0x24));
+const PORTB = @as(*volatile u8, @ptrFromInt(0x25));
+
+const DELAY = 100;
+
+pub export fn delay(n: u32) void {
+    var i: u32 = 0;
+    while (i < n) : (i += 1) {
+        asm volatile ("nop" ::: "memory");
+    }
+}
+
+pub export fn blink(n: u32) void {
+    var i: u32 = 0;
+    DDRB.* = DDRB.* | (1 << 5);
+
+    while (i < n) : (i += 1) {
+        // Toggle PB5
+        PORTB.* ^= @as(u8, 1 << 5);
+        delay(100_000);
+        PORTB.* ^= @as(u8, 1 << 5);
+        delay(200_000);
+    }
+}
+
+pub export fn collatz(na: u32) u32 {
+    var n: u32 = na;
+    var c: u32 = 0;
+
+    while (n > 1) : (c += 1) {
+        if (n % 2 == 0) {
+            n /= 2;
+        } else {
+            n = n + n + n + 1;
+        }
+    }
+
+    return c;
+}
+
+pub export fn main() void {
+    var i: u32 = 0;
+    while (true) : (i += 1) {
+        const c = collatz(i);
+        blink(c);
+        delay(500_000);
+    }
+}
+
+pub export fn abort() void {
+    // Set PB5 (pin 13) as output
+    DDRB.* = DDRB.* | (1 << 5);
+
+    while (true) {
+        // Toggle PB5
+        PORTB.* ^= @as(u8, 1 << 5);
+
+        // Simple delay
+        var i: usize = 0;
+        while (i < DELAY) : (i += 1) {
+            asm volatile ("nop" ::: "memory");
+        }
+    }
+}
diff --git a/build.zig b/build.zig
new file mode 100644
index 0000000..0a65c1f
--- /dev/null
+++ b/build.zig
@@ -0,0 +1,78 @@
+const std = @import("std");
+const Builder = std.Build;
+
+pub fn build(b: *std.Build) !void {
+    const uno = std.zig.CrossTarget{
+        .cpu_arch = .avr,
+        .cpu_model = .{ .explicit = &std.Target.avr.cpu.atmega328p },
+        .os_tag = .freestanding,
+        .abi = .none,
+    };
+
+    const exe = b.addExecutable(.{
+        .name = "blink",
+        .root_source_file = b.path("blink.zig"),
+        .target = b.resolveTargetQuery(uno),
+        .optimize = .ReleaseSafe,
+    });
+
+    const init = b.addObject(.{
+        .name = "startup",
+        .root_source_file = b.path("init.zig"),
+        .target = b.resolveTargetQuery(uno),
+        .optimize = .ReleaseSafe
+    });
+
+    exe.addObject(init);
+    exe.setLinkerScriptPath(b.path("linker.ld"));
+
+    b.installArtifact(exe);
+
+    const tty = b.option(
+        []const u8,
+        "tty",
+        "Specify the port to which the Arduino is connected (defaults to /dev/ttyACM0)",
+    ) orelse "/dev/ttyACM0";
+
+    const bin_path = b.getInstallPath(.{ .custom = exe.installed_path orelse "./bin" }, exe.out_filename);
+
+    const flash_command = blk: {
+        var tmp = std.ArrayList(u8).init(b.allocator);
+        try tmp.appendSlice("-Uflash:w:");
+        try tmp.appendSlice(bin_path);
+        try tmp.appendSlice(":e");
+        break :blk try tmp.toOwnedSlice();
+    };
+
+    const upload = b.step("upload", "Upload the code to an Arduino device using avrdude");
+    const avrdude = b.addSystemCommand(&.{
+        "avrdude",
+        "-carduino",
+        "-patmega328p",
+        "-D",
+        "-P",
+        tty,
+        flash_command,
+    });
+    upload.dependOn(&avrdude.step);
+    avrdude.step.dependOn(&exe.step);
+
+    const objdump = b.step("objdump", "Show dissassembly of the code using avr-objdump");
+    const avr_objdump = b.addSystemCommand(&.{
+        "avr-objdump",
+        "-dh",
+        bin_path,
+    });
+    objdump.dependOn(&avr_objdump.step);
+    avr_objdump.step.dependOn(&exe.step);
+
+    const monitor = b.step("monitor", "Opens a monitor to the serial output");
+    const screen = b.addSystemCommand(&.{
+        "screen",
+        tty,
+        "115200",
+    });
+    monitor.dependOn(&screen.step);
+
+    b.default_step.dependOn(&exe.step);
+}
diff --git a/init.zig b/init.zig
new file mode 100644
index 0000000..be0bd10
--- /dev/null
+++ b/init.zig
@@ -0,0 +1,27 @@
+pub export fn _start() linksection(".vectors") callconv(.Naked) void {
+    asm volatile (
+        \\ rjmp reset    ; jump to reset
+        \\ rjmp ext_int0
+    );
+}
+
+pub export const end_of_ram: u16 = 0x8FF;
+pub export fn reset() linksection(".vectors") callconv(.Naked) void {
+    asm volatile (
+        \\ sei
+        \\ rjmp main
+    );
+    // asm volatile (
+    //     \\ ldi r16, hi8(%[ramend])
+    //     \\ sts 0x3E, r16
+    //     \\ ldi r16, lo8(%[ramend])
+    //     \\ sts 0X3D, r16
+    //     \\ sei
+    //     \\ jmp main
+    //     :
+    //     : [ramend] "i" (end_of_ram)
+    //     : "r16"
+    // );
+}
+
+pub export fn ext_int0() void {}
diff --git a/linker.ld b/linker.ld
new file mode 100644
index 0000000..ef5e46b
--- /dev/null
+++ b/linker.ld
@@ -0,0 +1,33 @@
+MEMORY
+{
+    flash (rx) : ORIGIN = 0, LENGTH = 32K
+    ram (rw!x) : ORIGIN = 0x100, LENGTH = 2K
+}
+
+SECTIONS
+{
+    .text :
+    {
+        KEEP(*(.vectors))
+
+        *(.text*)
+    } > flash
+
+    .data :
+    {
+        __data_start = .;
+        *(.rodata*)
+        *(.data*)
+        __data_end = .;
+    } > ram AT> flash
+
+    .bss (NOLOAD) :
+    {
+        __bss_start = .;
+        *(.bss*)
+        __bss_end = .;
+    } > ram
+    RAMEND = ORIGIN(ram) + LENGTH(ram);
+
+    __data_load_start = LOADADDR(.data);
+}
-- 
cgit