mcu/nrf5340: Add API to switch lpclk in the runtime

Author: m-gorecki

hw/mcu/nordic/nrf5340/include/mcu/nrf5340_clock.h

@@ -43,6 +43,20 @@ int nrf5340_clock_hfxo_request(void);
  */
 int nrf5340_clock_hfxo_release(void);
 
+/**
+ * Request low frequency clock source change.
+ *
+ * @param  clksrc Value to determine requested clock source
+ *                This parameter can be one of the following values:
+ *                @arg CLOCK_LFCLKSTAT_SRC_LFRC - 32.768 kHz RC oscillator
+ *                @arg CLOCK_LFCLKSTAT_SRC_LFXO - 32.768 kHz crystal oscillator
+ *                @arg CLOCK_LFCLKSTAT_SRC_LFSYNT - 32.768 kHz synthesized from HFCLK
+ *
+ * @return int 0: clock source was already as requested. 1: clock source
+ *         changed.
+ */
+int nrf5340_set_lf_clock_source(uint32_t clksrc);
+
 /**
  * Request HFCLK192M clock be turned on. Note that each request must have a
  * corresponding release.

hw/mcu/nordic/nrf5340/src/nrf5340_clock.c

@@ -100,3 +100,58 @@ nrf5340_clock_hfclk192m_release(void)
 
     return stopped;
 }
+
+int
+nrf5340_set_lf_clock_source(uint32_t clksrc)
+{
+    uint32_t regmsk;
+    uint32_t regval;
+
+    regmsk = CLOCK_LFCLKSTAT_STATE_Msk | CLOCK_LFCLKSTAT_SRC_Msk;
+    regval = CLOCK_LFCLKSTAT_STATE_Running << CLOCK_LFCLKSTAT_STATE_Pos;
+
+    regval |= clksrc << CLOCK_LFCLKSTAT_SRC_Pos;
+
+    /* Check if this clock source isn't already running */
+    if ((NRF_CLOCK->LFCLKSTAT & regmsk) == regval) {
+        return 0;
+    }
+
+    /*
+     * Request HFXO if LFSYNTH is going to be set as source. If LFSYNTH is going to be
+     * replaced with other source, release HFXO.
+     */
+    if (clksrc == CLOCK_LFCLKSTAT_SRC_LFSYNT) {
+        if ((NRF_CLOCK->HFCLKSTAT & CLOCK_HFCLKSTAT_STATE_Msk) !=
+            (CLOCK_HFCLKSTAT_STATE_Running << CLOCK_HFCLKSTAT_STATE_Pos)) {
+            NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
+            nrf5340_clock_hfxo_request();
+            while (1) {
+                if ((NRF_CLOCK->EVENTS_HFCLKSTARTED) != 0) {
+                    break;
+                }
+            }
+        } else {
+            nrf5340_clock_hfxo_request();
+        }
+    } else if ((NRF_CLOCK->LFCLKSTAT & CLOCK_LFCLKSTAT_SRC_Msk) ==
+               CLOCK_LFCLKSTAT_SRC_LFSYNT) {
+        nrf5340_clock_hfxo_release();
+    }
+
+    NRF_CLOCK->TASKS_LFCLKSTOP = 1;
+    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
+    NRF_CLOCK->LFCLKSRC = clksrc;
+    NRF_CLOCK->TASKS_LFCLKSTART = 1;
+
+    /* Wait here till started! */
+    while (1) {
+        if (NRF_CLOCK->EVENTS_LFCLKSTARTED) {
+            if ((NRF_CLOCK->LFCLKSTAT & regmsk) == regval) {
+                break;
+            }
+        }
+    }
+
+    return 1;
+}