ch32v: Revamp the board-level usart setup design

examples/wch/ch32v/src/uart_log.zig

@@ -4,7 +4,7 @@ const hal = microzig.hal;
 const board = microzig.board;
 const time = hal.time;
 
-const uart_cfg: hal.usart.UartConfig = if (@hasDecl(board, "uart_config")) board.uart_config else .{};
+const uart = hal.usart.UartSetup.default;
 
 pub const panic = microzig.panic;
 
@@ -20,8 +20,8 @@ comptime {
 pub fn main() !void {
     board.init();
 
-    hal.usart.setup_uart(uart_cfg);
-    hal.usart.init_logger(uart_cfg.instance);
+    uart.apply(.{ .baud_rate = 115200 });
+    hal.usart.init_logger(uart.instance);
 
     var i: u32 = 0;
     while (true) : (i += 1) {

port/wch/ch32v/src/boards/LANA_TNY.zig

@@ -21,7 +21,7 @@ pub fn init() void {
 }
 
 /// Default UART: USART2 on PA2 (exposed on the board header)
-pub const uart_config: ch32v.usart.UartConfig = .{
+pub const uart_setup: ch32v.usart.UartSetup = .{
     .instance = .USART2,
     .tx_pin = ch32v.gpio.Pin.init(0, 2), // PA2
 };

port/wch/ch32v/src/boards/nanoCH32V203.zig

@@ -25,7 +25,10 @@ pub fn init() void {
 }
 
 /// Default UART: USART1 on PA9
-pub const uart_config: ch32v.usart.UartConfig = .{};
+pub const uart_setup: ch32v.usart.UartSetup = .{
+    .instance = .USART1,
+    .tx_pin = ch32v.gpio.Pin.init(0, 9), // PA9
+};
 
 pub const pin_config = ch32v.pins.GlobalConfiguration{
     .GPIOA = .{

port/wch/ch32v/src/hals/usart.zig

@@ -92,24 +92,27 @@ pub const ReceiveError = error{
 
 const gpio = hal.gpio;
 
-/// Configuration for board-level UART defaults.
-/// Boards export a `uart_config` const of this type with their preferred
-/// USART instance, TX pin, and serial settings. Examples can use these
-/// defaults directly or construct their own `UartConfig`.
-pub const UartConfig = struct {
-    instance: USART = .USART1,
-    tx_pin: gpio.Pin = gpio.Pin.init(0, 9), // PA9 (USART1 default TX)
-    config: Config = .{ .baud_rate = 115200 },
+/// Physical-layer UART setup: which USART instance and TX pin to use.
+/// Boards export a `uart_setup` const of this type. Application-level
+/// settings (baud rate, parity, etc.) are passed separately via `Config`.
+pub const UartSetup = struct {
+    instance: USART,
+    tx_pin: gpio.Pin,
+
+    /// Throw a compile error if an application tries to use the default, but
+    /// the board it is being compiled for does not provide one.
+    pub const default: UartSetup = if (microzig.config.has_board and @hasDecl(microzig.board, "uart_setup"))
+        microzig.board.uart_setup
+    else
+        @compileError("board does not provide a default uart_setup");
+
+    /// Apply settings
+    pub fn apply(comptime self: UartSetup, comptime config: Config) void {
+        self.tx_pin.configure_alternate_function(.push_pull, .max_50MHz);
+        self.instance.apply(config);
+    }
 };
 
-/// Configure a UART from a `UartConfig`: sets up the TX pin as alternate
-/// function push-pull, then applies the USART peripheral configuration
-/// (clock enable, AFIO remap, baud rate, etc.).
-pub fn setup_uart(comptime cfg: UartConfig) void {
-    cfg.tx_pin.configure_alternate_function(.push_pull, .max_50MHz);
-    cfg.instance.apply(cfg.config);
-}
-
 pub const instance = struct {
     pub const USART1: USART = .USART1;
     pub const USART2: USART = .USART2;