Fix ms/us confusion around watchdog time_remaining functions (#2533)

Fix documention for watchdog_get_time_remaining_ms and add a new watchdog_get_time_remaining_us
Fixes #2496

Author: lurch

src/rp2_common/hardware_watchdog/include/hardware/watchdog.h

@@ -134,14 +134,26 @@ bool watchdog_enable_caused_reboot(void);
  * \if rp2040_specific
  * On RP2040 this method returns the last value set instead of the remaining time due to a h/w bug.
  * \endif
- * 
+ *
  * @return The number of microseconds before the watchdog will reboot the chip.
  */
+uint32_t watchdog_get_time_remaining_us(void);
+
+/**
+ * \brief Returns the number of milliseconds before the watchdog will reboot the chip.
+ * \ingroup hardware_watchdog
+ *
+ * \if rp2040_specific
+ * On RP2040 this method returns the last value set instead of the remaining time due to a h/w bug.
+ * \endif
+ *
+ * @return The number of milliseconds before the watchdog will reboot the chip.
+ */
 uint32_t watchdog_get_time_remaining_ms(void);
 
 // backwards compatibility with SDK < 2.0.0
 static inline uint32_t watchdog_get_count(void) {
-    return watchdog_get_time_remaining_ms();
+    return watchdog_get_time_remaining_us();
 }
 #ifdef __cplusplus
 }

src/rp2_common/hardware_watchdog/watchdog.c

@@ -28,16 +28,21 @@ void watchdog_update(void) {
 }
 // end::watchdog_update[]
 
-uint32_t watchdog_get_time_remaining_ms(void) {
-    return watchdog_hw->ctrl & WATCHDOG_CTRL_TIME_BITS;
-}
-
 #if PICO_RP2040
-// Note, we have x2 here as the watchdog HW currently decrements twice per tick
+// Note, we have x2 here as the watchdog HW currently decrements twice per tick (errata RP2040-E1)
 #define WATCHDOG_XFACTOR 2
 #else
 #define WATCHDOG_XFACTOR 1
 #endif
+
+uint32_t watchdog_get_time_remaining_us(void) {
+    return (watchdog_hw->ctrl & WATCHDOG_CTRL_TIME_BITS) / WATCHDOG_XFACTOR;
+}
+
+uint32_t watchdog_get_time_remaining_ms(void) {
+    return (watchdog_hw->ctrl & WATCHDOG_CTRL_TIME_BITS) / (1000 * WATCHDOG_XFACTOR);
+}
+
 // tag::watchdog_enable[]
 // Helper function used by both watchdog_enable and watchdog_reboot
 void _watchdog_enable(uint32_t delay_ms, bool pause_on_debug) {
@@ -60,10 +65,7 @@ void _watchdog_enable(uint32_t delay_ms, bool pause_on_debug) {
     if (!delay_ms) {
         hw_set_bits(&watchdog_hw->ctrl, WATCHDOG_CTRL_TRIGGER_BITS);
     } else {
-        load_value = delay_ms * 1000;
-#if PICO_RP2040
-        load_value *= 2;
-#endif
+        load_value = delay_ms * (1000 * WATCHDOG_XFACTOR);
         if (load_value > WATCHDOG_LOAD_BITS)
             load_value = WATCHDOG_LOAD_BITS;