Implements usage of avr-gcc

Author: Felix "xq" Queißner

build.zig

@@ -26,6 +26,7 @@ pub const chips = struct {
             },
         },
         .hal = hal,
+        .binary_post_process = compileWithAvrGcc,
     };
 };
 
@@ -40,6 +41,7 @@ pub const boards = struct {
                 .url = "https://docs.arduino.cc/hardware/nano",
                 .source_file = path("/src/boards/arduino_nano.zig"),
             },
+            .binary_post_process = compileWithAvrGcc,
         };
 
         pub const uno_rev3 = .{
@@ -51,11 +53,50 @@ pub const boards = struct {
                 .url = "https://docs.arduino.cc/hardware/uno-rev3",
                 .source_file = path("/src/boards/arduino_uno.zig"),
             },
+            .binary_post_process = compileWithAvrGcc,
         };
     };
 };
 
-pub fn build(b: *std.build.Builder) void {
+fn compileWithAvrGcc(b: *std.Build, c_file: std.Build.LazyPath) std.Build.LazyPath {
+    const compile_step = @fieldParentPtr(std.Build.CompileStep, "step", c_file.generated.step);
+    if (compile_step.target.ofmt != .c) {
+        // sanity check: if not building a C file, skip.
+        return c_file;
+    }
+
+    const prog = b.findProgram(&.{"avr-gcc"}, &.{}) catch @panic("Please install avr-gcc!");
+
+    const lib_dir = if (b.zig_lib_dir) |lib_dir|
+        lib_dir.getPath(b)
+    else
+        b.pathJoin(&.{ std.fs.path.dirname(std.fs.path.dirname(b.zig_exe).?).?, "lib" });
+
+    const linker_script = compile_step.linker_script.?;
+
+    const compiler = b.addSystemCommand(&.{
+        prog,
+        "-g", // debug options
+        "-mmcu=avr5", // compile for avr5
+        "-Wno-builtin-declaration-mismatch", // hide weird zig warnings
+        "-I",
+        lib_dir,
+        "-nostartfiles", // do not link _start from avrlibc
+        "-ffreestanding", // do not link libc
+    });
+
+    compiler.addArg("-T");
+    compiler.addFileArg(linker_script);
+
+    compiler.addArg("-o");
+    const elf_file = compiler.addOutputFileArg("firmware.elf");
+
+    compiler.addFileArg(c_file);
+
+    return elf_file;
+}
+
+pub fn build(b: *std.Build) void {
     _ = b;
     // const optimize = b.standardOptimizeOption(.{});
     // inline for (@typeInfo(boards).Struct.decls) |decl| {