Add logging and panic handler

lvgltest.zig

@@ -44,6 +44,7 @@ pub export fn lvgltest_main(
     _argc: c_int, 
     _argv: [*]const [*]const u8
 ) c_int {
+    debug("Zig LVGL Test", .{});
     _ = _argc;
     _ = _argv;
     var disp_drv: ?*c.lv_disp_drv_t = c.get_disp_drv();
@@ -88,3 +89,76 @@ pub fn monitor_cb(arg_disp_drv: ?*c.lv_disp_drv_t, arg_time_1: u32, arg_px: u32)
     var px = arg_px;
     _ = px;
 }
+
+///////////////////////////////////////////////////////////////////////////////
+//  Panic Handler
+
+/// Called by Zig when it hits a Panic. We print the Panic Message, Stack Trace and halt. See 
+/// https://andrewkelley.me/post/zig-stack-traces-kernel-panic-bare-bones-os.html
+/// https://github.com/ziglang/zig/blob/master/lib/std/builtin.zig#L763-L847
+pub fn panic(
+    message: []const u8, 
+    _stack_trace: ?*std.builtin.StackTrace
+) noreturn {
+    // Print the Panic Message
+    _ = _stack_trace;
+    _ = puts("\n!ZIG PANIC!");
+    _ = puts(@ptrCast([*c]const u8, message));
+
+    // Print the Stack Trace
+    _ = puts("Stack Trace:");
+    var it = std.debug.StackIterator.init(@returnAddress(), null);
+    while (it.next()) |return_address| {
+        _ = printf("%p\n", return_address);
+    }
+
+    // Halt
+    while(true) {}
+}
+
+///////////////////////////////////////////////////////////////////////////////
+//  Logging
+
+/// Called by Zig for `std.log.debug`, `std.log.info`, `std.log.err`, ...
+/// https://gist.github.com/leecannon/d6f5d7e5af5881c466161270347ce84d
+pub fn log(
+    comptime _message_level: std.log.Level,
+    comptime _scope: @Type(.EnumLiteral),
+    comptime format: []const u8,
+    args: anytype,
+) void {
+    _ = _message_level;
+    _ = _scope;
+
+    // Format the message
+    var buf: [100]u8 = undefined;  // Limit to 100 chars
+    var slice = std.fmt.bufPrint(&buf, format, args)
+        catch { _ = puts("*** log error: buf too small"); return; };
+
+    // Terminate the formatted message with a null
+    var buf2: [buf.len + 1 : 0]u8 = undefined;
+    std.mem.copy(
+        u8, 
+        buf2[0..slice.len], 
+        slice[0..slice.len]
+    );
+    buf2[slice.len] = 0;
+
+    // Print the formatted message
+    _ = puts(&buf2);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+//  Imported Functions and Variables
+
+/// For safety, we import these functions ourselves to enforce Null-Terminated Strings.
+/// We changed `[*c]const u8` to `[*:0]const u8`
+extern fn printf(format: [*:0]const u8, ...) c_int;
+extern fn puts(str: [*:0]const u8) c_int;
+
+/// LoRaWAN Event Queue
+extern var event_queue: c.struct_ble_npl_eventq;
+
+/// Aliases for Zig Standard Library
+const assert = std.debug.assert;
+const debug  = std.log.debug;