- Added support for RP2040's RTC peripheral (#317)

- Added example showing how the RTC is used

Co-authored-by: Hayden Riddiford <[email protected]>

examples/raspberrypi/rp2xxx/build.zig

@@ -19,6 +19,7 @@ pub fn build(b: *std.Build) void {
         .{ .target = mb.ports.rp2xxx.boards.raspberrypi.pico, .name = "pico_i2c-bus-scan", .file = "src/rp2040_only/i2c_bus_scan.zig" },
         .{ .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" },

examples/raspberrypi/rp2xxx/src/rp2040_only/rtc.zig

@@ -0,0 +1,102 @@
+const std = @import("std");
+const microzig = @import("microzig");
+const rp2xxx = microzig.hal;
+const time = rp2xxx.time;
+
+const pin_config = rp2xxx.pins.GlobalConfiguration{
+    .GPIO25 = .{
+        .name = "led",
+        .direction = .out,
+    },
+};
+
+pub const microzig_options = .{
+    .interrupts = .{
+        .RTC_IRQ = .{ .C = &rtc_isr },
+    },
+};
+
+/// Enables/disables interrupts to prevent data-races with variables
+/// shared between ISRs and normal code
+///
+/// TODO: microzig/core/src/interrupt.zig might provide a more general implementation
+///       for this in the future.
+const CriticalSection = struct {
+    isr_reg_value: usize = 0,
+
+    pub fn enter(self: *CriticalSection) void {
+        var val: usize = undefined;
+        asm volatile (
+            \\mrs   %[val], primask
+            \\movs  r1, #1
+            \\msr   primask, r1
+            : [val] "=r" (val),
+            :
+            : "r1", "cc"
+        );
+        self.isr_reg_value = val;
+    }
+
+    pub fn exit(self: *CriticalSection) void {
+        const val = self.isr_reg_value;
+        asm volatile ("msr   primask, %[val]"
+            :
+            : [val] "r" (val),
+        );
+    }
+};
+var critical_section: CriticalSection = .{};
+
+var _fast_blink: bool = false;
+/// Access underlying _sleep_time via volatile * to prevent reads from being optimized away
+var fast_blink_vp: *volatile bool = &_fast_blink;
+
+fn rtc_isr() callconv(.C) void {
+
+    // Important to disable + re-enable the RTC alarm so that the interrupt doesn't
+    // continue firing for the entire time the alarm condition is met
+    // (For example, it would fire the entire second that it matches the desired "second" count)
+    rp2xxx.rtc.alarm.disable();
+    rp2xxx.rtc.alarm.enable();
+
+    // Every 1 minute, alternate between fast and slow blinking
+    critical_section.enter();
+    fast_blink_vp.* = !fast_blink_vp.*;
+    critical_section.exit();
+}
+
+pub fn main() !void {
+    const pins = pin_config.apply();
+
+    // Configure initial datetime for RTC
+    rp2xxx.rtc.set_datetime(.{
+        .year = 2024,
+        .month = 12,
+        .day = 25,
+        .day_of_week = .Monday,
+        .hour = 0,
+        .minute = 0,
+        .second = 0,
+    });
+    rp2xxx.rtc.apply(rp2xxx.clock_config);
+
+    // Configure an alarm that goes off once a minute (whenever second == 0)
+    rp2xxx.rtc.alarm.configure(.{ .second = 0 });
+
+    // Enable peripheral level alarm
+    rp2xxx.rtc.irq.enable();
+
+    // Enable top level NVIC alarm
+    rp2xxx.irq.enable(.RTC_IRQ);
+
+    while (true) {
+
+        // Disable interrupts during volatile read of fast_blink to prevent data races
+        critical_section.enter();
+        const fast_blink = fast_blink_vp.*;
+        critical_section.exit();
+
+        pins.led.toggle();
+        time.sleep_ms(if (fast_blink) 500 else 1000);
+    }
+}

port/raspberrypi/rp2xxx/src/hal.zig

@@ -15,6 +15,10 @@ pub const pwm = @import("hal/pwm.zig");
 pub const rand = @import("hal/random.zig");
 pub const resets = @import("hal/resets.zig");
 pub const rom = @import("hal/rom.zig");
+pub const rtc = switch (compatibility.cpu) {
+    .RP2040 => @import("hal/rtc.zig"),
+    .RP2350 => {}, // No explicit "RTC" module on RP2350
+};
 pub const spi = @import("hal/spi.zig");
 pub const i2c = @import("hal/i2c.zig");
 pub const time = @import("hal/time.zig");

port/raspberrypi/rp2xxx/src/hal/clocks/rp2040.zig

@@ -300,7 +300,7 @@ pub const config = struct {
         ///     - TODO: Could vary the PLL frequency based on sys_freq input to open up a broader range of SYS frequencies
         /// - CLK_USB sourced from PLL_USB @ 48 MHz
         /// - CLK_ADC sourced from PLL_USB @ 48 MHz
-        /// - CLK_RTC sourced from CLK_SYS
+        /// - CLK_RTC sourced from PLL_USB @ 48 MHz and divided down to ~65484 Hz
         /// - CLK_PERI sourced from CLK_SYS
         pub fn system(sys_freq: u32, ref_freq: u32) Global {
             var cfg: Global = .{};
@@ -359,14 +359,15 @@ pub const config = struct {
                 .integer_divisor = 1,
             };
 
-            // RTC gets connected to PLL_USB
+            // RTC gets connected to PLL_USB, and divided down to ~65484 Hz in order
+            // to be a suitable clock for 1 second reference.
             cfg.rtc =
                 .{
                 .input = .{
                     .source = .pll_usb,
                     .freq = 48_000_000,
                 },
-                .integer_divisor = 1,
+                .integer_divisor = 733,
             };
 
             // CLK_PERI is sourced from CLK_SYS, divisor hard coded to 1 on RP2040