added method to get alarm_pool core_num so stdio_usb_init can fail early

src/common/pico_time/include/pico/time.h

@@ -403,6 +403,14 @@ alarm_pool_t *alarm_pool_create(uint hardware_alarm_num, uint max_timers);
  */
 uint alarm_pool_hardware_alarm_num(alarm_pool_t *pool);
 
+/**
+ * \brief Return the core number the alarm pool was initialized on (and hence callbacks are called on)
+ * \ingroup alarm
+ * \param pool the pool
+ * \return the core used by the pool
+ */
+uint alarm_pool_core_num(alarm_pool_t *pool);
+
 /**
  * \brief Destroy the alarm pool, cancelling all alarms and freeing up the underlying hardware alarm
  * \ingroup alarm

src/common/pico_time/time.c

@@ -31,6 +31,7 @@ typedef struct alarm_pool {
     uint8_t *entry_ids_high;
     alarm_id_t alarm_in_progress; // this is set during a callback from the IRQ handler... it can be cleared by alarm_cancel to prevent repeats
     uint8_t hardware_alarm_num;
+    uint8_t core_num;
 } alarm_pool_t;
 
 #if !PICO_TIME_DEFAULT_ALARM_POOL_DISABLED
@@ -190,6 +191,7 @@ void alarm_pool_post_alloc_init(alarm_pool_t *pool, uint hardware_alarm_num) {
     hardware_alarm_set_callback(hardware_alarm_num, alarm_pool_alarm_callback);
     pool->lock = spin_lock_instance(next_striped_spin_lock_num());
     pool->hardware_alarm_num = (uint8_t) hardware_alarm_num;
+    pool->core_num = get_core_num();
     pools[hardware_alarm_num] = pool;
 }
 
@@ -286,6 +288,10 @@ uint alarm_pool_hardware_alarm_num(alarm_pool_t *pool) {
     return pool->hardware_alarm_num;
 }
 
+uint alarm_pool_core_num(alarm_pool_t *pool) {
+    return pool->core_num;
+}
+
 static void alarm_pool_dump_key(pheap_node_id_t id, void *user_data) {
     alarm_pool_t *pool = (alarm_pool_t *)user_data;
 #if PICO_ON_DEVICE

src/rp2_common/pico_stdio/include/pico/stdio.h

@@ -52,9 +52,10 @@ typedef struct stdio_driver stdio_driver_t;
  * When stdio_usb is configured, this method can be optionally made to block, waiting for a connection
  * via the variables specified in \ref stdio_usb_init (i.e. \ref PICO_STDIO_USB_CONNECT_WAIT_TIMEOUT_MS)
  *
+ * \return true if at least one output was successfully initialized, false otherwise.
  * \see stdio_uart, stdio_usb, stdio_semihosting
  */
-void stdio_init_all(void);
+bool stdio_init_all(void);
 
 /*! \brief Initialize all of the present standard stdio types that are linked into the binary.
  * \ingroup pico_stdio

src/rp2_common/pico_stdio/stdio.c

@@ -267,20 +267,25 @@ int __printflike(1, 0) WRAPPER_FUNC(printf)(const char* format, ...)
     return ret;
 }
 
-void stdio_init_all(void) {
+bool stdio_init_all(void) {
     // todo add explicit custom, or registered although you can call stdio_enable_driver explicitly anyway
     // These are well known ones
+
+    bool rc = false;
 #if LIB_PICO_STDIO_UART
     stdio_uart_init();
+    rc = true;
 #endif
 
 #if LIB_PICO_STDIO_SEMIHOSTING
     stdio_semihosting_init();
+    rc = true;
 #endif
 
 #if LIB_PICO_STDIO_USB
-    stdio_usb_init();
+    rc |= stdio_usb_init();
 #endif
+    return rc;
 }
 
 int WRAPPER_FUNC(getchar)(void) {

src/rp2_common/pico_stdio_usb/stdio_usb.c

@@ -38,7 +38,6 @@ static uint8_t low_priority_irq_num;
 #endif
 
 static int64_t timer_task(__unused alarm_id_t id, __unused void *user_data) {
-    assert(stdio_usb_core_num == get_core_num()); // if this fails, you have initialized stdio_usb on the wrong core
     int64_t repeat_time;
     if (critical_section_is_initialized(&one_shot_timer_crit_sec)) {
         critical_section_enter_blocking(&one_shot_timer_crit_sec);
@@ -147,6 +146,12 @@ stdio_driver_t stdio_usb = {
 };
 
 bool stdio_usb_init(void) {
+    if (get_core_num() != alarm_pool_core_num(alarm_pool_get_default())) {
+        // included an assertion here rather than just returning false, as this is likely
+        // a coding bug, rather than anything else.
+        assert(false);
+        return false;
+    }
 #ifndef NDEBUG
     stdio_usb_core_num = (uint8_t)get_core_num();
 #endif