From f4bf5658970543f26f25816b9123ecfd258bdd42 Mon Sep 17 00:00:00 2001
From: Clyne Sullivan <clyne@bitgloo.com>
Date: Sun, 6 Oct 2024 16:01:53 -0400
Subject: [PATCH] better startup: all zig, bss and data init'd

---
 build.zig       |  3 +--
 link.ld         | 10 +++++-----
 src/bootstrap.s | 13 -------------
 src/main.zig    |  2 +-
 src/startup.zig | 41 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 48 insertions(+), 21 deletions(-)
 delete mode 100644 src/bootstrap.s
 create mode 100644 src/startup.zig

diff --git a/build.zig b/build.zig
index 00d19c4..8493bbb 100644
--- a/build.zig
+++ b/build.zig
@@ -10,14 +10,13 @@ pub fn build(b: *std.Build) void {
 
     const exe = b.addExecutable(.{
         .name = "stm32",
-        .root_source_file = b.path("src/main.zig"),
+        .root_source_file = b.path("src/startup.zig"),
         .target = target,
         //.optimize = .Debug,
         .optimize = .ReleaseSafe,
         .linkage = .static,
     });
 
-    exe.addAssemblyFile(b.path("src/bootstrap.s"));
     exe.setLinkerScriptPath(b.path("link.ld"));
 
     b.installArtifact(exe);
diff --git a/link.ld b/link.ld
index e777ac4..f5011ba 100644
--- a/link.ld
+++ b/link.ld
@@ -23,24 +23,24 @@ SECTIONS {
 	} > FLASH
 
 	/* initialized data */
-	_sidata = LOADADDR(.data);
+	__data_flash = LOADADDR(.data);
 	.data : {
 		. = ALIGN(8);
-		_sdata = .;
+		__data = .;
 		*(.data)
 		*(.data*)
 		. = ALIGN(8);
-		_edata = .;
+		__data_size = . - __data;
 	} > RAM AT > FLASH
 
 	/* uninitialized data */
 	.bss : {
 		. = ALIGN(8);
-		_sbss = .;
+		__bss = .;
 		*(.bss)
 		*(.bss*)
 		. = ALIGN(8);
-		_ebss = .;
+		__bss_size = . - __bss;
 	} > RAM
 
 	.stack : {
diff --git a/src/bootstrap.s b/src/bootstrap.s
deleted file mode 100644
index 612fac3..0000000
--- a/src/bootstrap.s
+++ /dev/null
@@ -1,13 +0,0 @@
-.cpu cortex-m4
-.thumb
-
-.extern _start
-.extern _tstack
-
-.section .vector_table
-.global init_vector_table
-init_vector_table:
-    .word _tstack
-    .word _start
-    .skip 4 * 14
-
diff --git a/src/main.zig b/src/main.zig
index d6a1aa4..99cb451 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -8,7 +8,7 @@ const gpioa = gpio.gpioa;
 const gpioc = gpio.gpioc;
 const tick = timer.systick;
 
-export fn _start() callconv(.C) noreturn {
+pub fn main() void {
     cpu.interrupt_disable();
     interrupt.initialize();
     interrupt.register(.SVCall, svcall);
diff --git a/src/startup.zig b/src/startup.zig
new file mode 100644
index 0000000..f7c7712
--- /dev/null
+++ b/src/startup.zig
@@ -0,0 +1,41 @@
+const main = @import("main.zig");
+
+extern const __data_flash: u32;
+extern const __data: u32;
+extern const __data_size: u32;
+extern const __bss: u32;
+extern const __bss_size: u32;
+
+comptime {
+    asm (
+        \\.extern _start
+        \\.extern _tstack
+        \\
+        \\.section .vector_table
+        \\.global init_vector_table
+        \\init_vector_table:
+        \\    .word _tstack
+        \\    .word _start
+        \\    .skip 4 * 14
+    );
+}
+
+inline fn zero_bss() void {
+    const bss: [*]volatile u8 = @ptrFromInt(@intFromPtr(&__bss));
+    @memset(bss[0..@intFromPtr(&__bss_size)], 0);
+}
+
+inline fn copy_data() void {
+    const data_flash: [*]volatile u8 = @ptrFromInt(@intFromPtr(&__data_flash));
+    const data: [*]volatile u8 = @ptrFromInt(@intFromPtr(&__data));
+    const data_size = @intFromPtr(&__data_size);
+    @memcpy(data[0..data_size], data_flash[0..data_size]);
+}
+
+export fn _start() callconv(.C) noreturn {
+    zero_bss();
+    copy_data();
+    main.main();
+    while (true) {}
+}
+