rp2040: Add spi slave example (#391)

examples/raspberrypi/rp2xxx/build.zig

@@ -20,7 +20,6 @@ pub fn build(b: *std.Build) void {
         .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_pwm", .file = "src/rp2040_only/pwm.zig" },
         .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_random", .file = "src/rp2040_only/random.zig" },
         .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_rtc", .file = "src/rp2040_only/rtc.zig" },
-        .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_spi-host", .file = "src/rp2040_only/spi_host.zig" },
         .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_uart-echo", .file = "src/rp2040_only/uart_echo.zig" },
         .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_uart-log", .file = "src/rp2040_only/uart_log.zig" },
         .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_usb-hid", .file = "src/rp2040_only/usb_hid.zig" },
@@ -40,6 +39,8 @@ pub fn build(b: *std.Build) void {
     };
 
     const chip_agnostic_examples: []const ChipAgnosticExample = &.{
+        .{ .name = "spi-master", .file = "src/spi_master.zig" },
+        .{ .name = "spi-slave", .file = "src/spi_slave.zig" },
         .{ .name = "squarewave", .file = "src/squarewave.zig" },
         .{ .name = "ws2812", .file = "src/ws2812.zig" },
         .{ .name = "blinky", .file = "src/blinky.zig" },

examples/raspberrypi/rp2xxx/src/spi_master.zig

@@ -0,0 +1,37 @@
+const std = @import("std");
+const microzig = @import("microzig");
+
+const rp2xxx = microzig.hal;
+const time = rp2xxx.time;
+const gpio = rp2xxx.gpio;
+
+const BUF_LEN = 0x100;
+const spi = rp2xxx.spi.instance.SPI0;
+
+// These may change depending on which GPIO pins you have your SPI device routed to.
+const CS_PIN = 17;
+const SCK_PIN = 18;
+// NOTE: rp2xxx doesn't label pins as MOSI/MISO. Instead a pin is always for
+// either receiving or transmitting SPI data, no matter whether the chip is in
+// master or slave mode.
+const TX_PIN = 19;
+
+// Communicate with another RP2040 over spi
+pub fn main() !void {
+    // Set pin functions for CS, SCK, RX
+    const csn = rp2xxx.gpio.num(CS_PIN);
+    const mosi = rp2xxx.gpio.num(TX_PIN);
+    const sck = rp2xxx.gpio.num(SCK_PIN);
+    inline for (&.{ csn, mosi, sck }) |pin| {
+        pin.set_function(.spi);
+    }
+
+    try spi.apply(.{ .clock_config = rp2xxx.clock_config });
+    var out_buf: [BUF_LEN]u8 = .{ 'h', 'e', 'y', ' ', 'y', 'o', 'u', '!' } ** (BUF_LEN / 8);
+
+    while (true) {
+        std.log.info("Sending some data\n", .{});
+        spi.write_blocking(u8, &out_buf);
+        time.sleep_ms(1 * 1000);
+    }
+}

examples/raspberrypi/rp2xxx/src/spi_slave.zig

@@ -0,0 +1,62 @@
+const std = @import("std");
+const microzig = @import("microzig");
+
+const rp2xxx = microzig.hal;
+const time = rp2xxx.time;
+const gpio = rp2xxx.gpio;
+const chip = rp2xxx.compatibility.chip;
+
+const BUF_LEN = 0x100;
+const spi = rp2xxx.spi.instance.SPI0;
+
+const uart = rp2xxx.uart.instance.num(0);
+const uart_baud_rate = 115200;
+const uart_tx_pin = gpio.num(0);
+
+// These may change depending on which GPIO pins you have your SPI device routed to.
+const CS_PIN = 17;
+const SCK_PIN = 18;
+// NOTE: rp2xxx doesn't label pins as MOSI/MISO. Instead a pin is always for
+// either receiving or transmitting SPI data, no matter whether the chip is in
+// master or slave mode.
+const RX_PIN = 16;
+
+pub const microzig_options = .{
+    .log_level = .debug,
+    .logFn = rp2xxx.uart.logFn,
+};
+
+pub fn main() !void {
+    // Set pin functions for CS, SCK, RX
+    const csn = gpio.num(CS_PIN);
+    const mosi = gpio.num(RX_PIN);
+    const sck = gpio.num(SCK_PIN);
+    inline for (&.{ csn, mosi, sck }) |pin| {
+        pin.set_function(.spi);
+    }
+
+    switch (chip) {
+        .RP2040 => uart_tx_pin.set_function(.uart),
+        .RP2350 => uart_tx_pin.set_function(.uart_first),
+    }
+    uart.apply(.{
+        .baud_rate = uart_baud_rate,
+        .clock_config = rp2xxx.clock_config,
+    });
+
+    rp2xxx.uart.init_logger(uart);
+
+    std.log.info("Setting SPI as slave device", .{});
+    spi.set_slave(true);
+
+    try spi.apply(.{ .clock_config = rp2xxx.clock_config });
+    var in_buf: [BUF_LEN]u8 = undefined;
+
+    std.log.info("Reading", .{});
+
+    while (true) {
+        spi.read_blocking(u8, 0, &in_buf);
+        std.log.info("Got: {s}", .{in_buf});
+        time.sleep_ms(1 * 1000);
+    }
+}

port/raspberrypi/rp2xxx/src/hal/spi.zig

@@ -4,7 +4,6 @@ const peripherals = microzig.chip.peripherals;
 const SPI0_reg = peripherals.SPI0;
 const SPI1_reg = peripherals.SPI1;
 
-const gpio = @import("gpio.zig");
 const clocks = @import("clocks.zig");
 const resets = @import("resets.zig");
 const time = @import("time.zig");
@@ -162,6 +161,17 @@ pub const SPI = enum(u1) {
         spi_regs.SSPCPSR.modify(.{ .CPSDVSR = 0 });
     }
 
+    pub fn set_slave(spi: SPI, slave: bool) void {
+        const regs = spi.get_regs();
+        // Disable SPI
+        regs.SSPCR1.modify(.{ .SSE = 0 });
+
+        regs.SSPCR1.modify(.{ .MS = @intFromBool(slave) });
+
+        // Re-enable SPI
+        regs.SSPCR1.modify(.{ .SSE = 1 });
+    }
+
     pub inline fn is_writable(spi: SPI) bool {
         return spi.get_regs().SSPSR.read().TNF == 1;
     }
@@ -336,7 +346,7 @@ pub const SPI = enum(u1) {
     /// be 0, but some devices require a specific value here,
     /// e.g. SD cards expect 0xff
     ///
-    /// NOTE: This function is a vectored version of `write_blocking` and takes an array of arrays.
+    /// NOTE: This function is a vectored version of `read_blocking` and takes an array of arrays.
     ///       This pattern allows one to create better zero-copy send routines as message prefixes and
     ///       suffixes won't need to be concatenated/inserted to the original buffer, but can be managed
     ///       in a separate memory.