use interrupts instead of FreeRTOS tasks -- seems to work with both cores?

examples/RP2040ClockBlink/RP2040ClockBlink.ino

@@ -11,6 +11,8 @@
 
 #include <uClock.h>
 
+#define ATOMIC(X) { uint32_t __interrupt_mask = save_and_disable_interrupts(); X; restore_interrupts(__interrupt_mask); }
+
 uint8_t bpm_blink_timer = 1;
 void handle_bpm_led(uint32_t tick)
 {
@@ -50,14 +52,14 @@ void setup() {
 
   // A led to count bpms
   pinMode(LED_BUILTIN, OUTPUT);
-  digitalWrite(LED_BUILTIN, HIGH);
+  /*digitalWrite(LED_BUILTIN, HIGH);
   delay(500);
   digitalWrite(LED_BUILTIN, LOW);
   delay(500);
   digitalWrite(LED_BUILTIN, HIGH);
   delay(500);
   digitalWrite(LED_BUILTIN, LOW);
-  delay(500);
+  delay(500);*/
 
   
   Serial.begin(115200);
@@ -88,5 +90,5 @@ void loop() {
   //MIDI_USB.read();
   //count++;
   //if (millis()%1000==0)
-  //  Serial.println("looped!");
+  //  ATOMIC(Serial.println("looped!"));
 }

examples/RP2040UsbMasterMidiClock/RP2040UsbMasterMidiClock.ino

@@ -9,11 +9,16 @@
 
 Adafruit_USBD_MIDI usb_midi;
 MIDI_CREATE_INSTANCE(Adafruit_USBD_MIDI, usb_midi, MIDI_USB);
+//MIDI_CREATE_INSTANCE(HardwareSerial, Serial1, MIDI);
+
+#include <uClock.h>
 
+#define ATOMIC(X) { uint32_t __interrupt_mask = save_and_disable_interrupts(); X; restore_interrupts(__interrupt_mask); }
 //#define LED_BUILTIN PIN_LED_B
+//#define WAIT_FOR_SERIAL
+#define ENABLE_MULTICORE    
 
-//MIDI_CREATE_INSTANCE(HardwareSerial, Serial1, MIDI);
+volatile uint32_t count = 0;
-#include <uClock.h>
 
 uint8_t bpm_blink_timer = 1;
 void handle_bpm_led(uint32_t tick)
@@ -36,6 +41,8 @@ void onSync24Callback(uint32_t tick) {
   // Send MIDI_CLOCK to external gears
   MIDI_USB.sendRealTime(midi::Clock);
   handle_bpm_led(tick);
+
+  Serial.printf("ticked with %u\n", tick);
 }
 
 void onClockStart() {
@@ -46,6 +53,16 @@ void onClockStop() {
   MIDI_USB.sendRealTime(midi::Stop);
 }
 
+#ifdef ENABLE_MULTICORE
+  void setup1() {
+  }
+
+  void loop1() {
+    if (count%1000==0)
+      ATOMIC(Serial.println("loop1()!"); Serial.flush());
+  }
+#endif
+
 void setup() {
 #if defined(ARDUINO_ARCH_MBED) && defined(ARDUINO_ARCH_RP2040)
   // Manual begin() is required on core without built-in support for TinyUSB such as mbed rp2040
@@ -58,8 +75,10 @@ void setup() {
   pinMode(LED_BUILTIN, OUTPUT);
   
   Serial.begin(115200);
+  #ifdef WAIT_FOR_SERIAL
     while (!Serial)
       delay(1);
+  #endif
   
   // wait until device mounted
   /*while( !TinyUSBDevice.mounted() ) {
@@ -78,19 +97,18 @@ void setup() {
   uClock.setOnClockStart(onClockStart);  
   uClock.setOnClockStop(onClockStop);
   // Set the clock BPM to 126 BPM
-  uClock.setTempo(126);
+  uClock.setTempo(60);
   // Starts the clock, tick-tac-tick-tac..
   Serial.println("about to uClock.start()..."); Serial.flush();
   uClock.start();
-  Serial.println("uClock.start()ed!"); Serial.flush();
+  ATOMIC(Serial.println("uClock.start()ed!"); Serial.flush();)
 }
 
-uint32_t count = 0;
 
 // Do it whatever to interface with Clock.stop(), Clock.start(), Clock.setTempo() and integrate your environment...
 void loop() {
   MIDI_USB.read();
   count++;
   if (millis()%1000==0)
-    Serial.println("looped!!!");
+    ATOMIC(Serial.println("loop()!"); Serial.flush(););
 }

src/platforms/rp2040.h

@@ -1,8 +1,45 @@
 #include <Arduino.h>
+#include "pico/sync.h"
+
+#define MULTICORE
+
+#ifdef MULTICORE
+    // use interrupt version -- works for 2 cores ie can run loop1() and loop() simultaneously as well as the clock callback?
+
+    // RPi-specific timer
+    struct repeating_timer timer;
+
+    #define ATOMIC(X) { uint32_t __interrupt_mask = save_and_disable_interrupts(); X; restore_interrupts(__interrupt_mask); }
+
+    // forward declaration of uClockHandler
+    void uClockHandler();
+
+    // ISR handler -- called when tick happens
+    bool handlerISR(repeating_timer *timer)
+    {
+        uClockHandler();
+
+        return true;
+    }
+
+    void initTimer(uint32_t init_clock)
+    {
+        // set up RPi interrupt timer
+        // todo: actually should be -init_clock so that timer is set to start init_clock us after last tick, instead of init_clock us after finished processing last tick!
+        add_repeating_timer_us(init_clock, &handlerISR, NULL, &timer);
+    }
+
+    void setTimer(uint32_t us_interval) {
+        cancel_repeating_timer(&timer);
+        // todo: actually should be -init_clock so that timer is set to start init_clock us after last tick, instead of init_clock us after finished processing last tick!
+        add_repeating_timer_us(us_interval, &handlerISR, NULL, &timer);
+    }
+#else
+    // use FreeRTOS scheduling/mutex version -- doesn't work (task starts but does not run) if using loop1() ie core 2
+
     #include "FreeRTOS.h"
     #include <task.h>
     #include <semphr.h>
-#include "pico/sync.h"
 
     // RPi-specific timer
     struct repeating_timer timer;
@@ -48,10 +85,14 @@ void initTimer(uint32_t init_clock)
         xTaskCreate(clockTask, "clockTask", CLOCK_STACK_SIZE, NULL, 1, &taskHandle);
 
         // set up RPi interrupt timer
+        // todo: actually should be -init_clock so that timer is set to start init_clock us after last tick, instead of init_clock us after finished processing last tick!
         add_repeating_timer_us(init_clock, &handlerISR, NULL, &timer);
     }
 
     void setTimer(uint32_t us_interval) {
         cancel_repeating_timer(&timer);
+        // todo: actually should be -init_clock so that timer is set to start init_clock us after last tick, instead of init_clock us after finished processing last tick!
         add_repeating_timer_us(us_interval, &handlerISR, NULL, &timer);
     }
+
+#endif