hw/bsp/nrf53: Add syscfg for LFXO frequency

This allows to run nRF53 with 32000Hz LFXO.

Author: andrzej-kaczmarek

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

@@ -29,7 +29,11 @@
     #error The OS scheduler requires a low-frequency timer; configure MCU_LFCLK_SOURCE
 #endif
 
-#define RTC_FREQ            32768       /* in Hz */
+#if MYNEWT_VAL_CHOICE(MCU_LFCLK_SOURCE, LFXO)
+#define RTC_FREQ            (MYNEWT_VAL(MCU_LFXO_FREQ))
+#else
+#define RTC_FREQ            (32768) /* Hz */
+#endif
 #define OS_TICK_TIMER       NRF_RTC1
 #define OS_TICK_IRQ         RTC1_IRQn
 #define OS_TICK_CMPREG      3

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

@@ -43,6 +43,12 @@ typedef void (*hal_timer_irq_handler_t)(void);
 /* Maximum timer frequency */
 #define NRF5340_MAX_TIMER_FREQ    (16000000)
 
+#if MYNEWT_VAL_CHOICE(MCU_LFCLK_SOURCE, LFXO)
+#define LFCLK_FREQ              (MYNEWT_VAL(MCU_LFXO_FREQ))
+#else
+#define LFCLK_FREQ              (32768) /* Hz */
+#endif
+
 struct nrf5340_hal_timer {
     uint8_t tmr_enabled;
     uint8_t tmr_irq_num;
@@ -539,8 +545,8 @@ hal_timer_config(int timer_num, uint32_t freq_hz)
 
 #if (MYNEWT_VAL(TIMER_3) || MYNEWT_VAL(TIMER_4))
     if ((timer_num == 3) || (timer_num == 4)) {
-        /* NOTE: we only allow the RTC frequency to be set at 32768 */
-        if (bsptimer->tmr_enabled || (freq_hz != 32768) ||
+        /* NOTE: we only allow the RTC frequency to be set to LFCLK freq */
+        if (bsptimer->tmr_enabled || (freq_hz != LFCLK_FREQ) ||
             (bsptimer->tmr_reg == NULL)) {
             rc = EINVAL;
             goto err;

hw/mcu/nordic/nrf5340/syscfg.yml

@@ -65,6 +65,11 @@ syscfg.defs:
             - c7pf      # 7pF internal load capacitance
             - c9pf      # 9pF internal load capacitance
 
+    MCU_LFXO_FREQ:
+        description: >
+            Frequency of LFXO oscillator.
+        value: 32768
+
     MCU_HFXO_INTCAP:
         description: >
             Control usage of internal load capacitors for 32 MHz crystal

hw/mcu/nordic/nrf5340_net/src/hal_os_tick.c

@@ -28,7 +28,11 @@
     #error The OS scheduler requires a low-frequency timer; configure MCU_LFCLK_SOURCE
 #endif
 
-#define RTC_FREQ            32768       /* in Hz */
+#if MYNEWT_VAL_CHOICE(MCU_LFCLK_SOURCE, LFXO)
+#define RTC_FREQ            (MYNEWT_VAL(MCU_LFXO_FREQ))
+#else
+#define RTC_FREQ            (32768) /* Hz */
+#endif
 #define OS_TICK_TIMER       NRF_RTC1_NS
 #define OS_TICK_IRQ         RTC1_IRQn
 #define OS_TICK_CMPREG      3

hw/mcu/nordic/nrf5340_net/src/hal_timer.c

@@ -43,6 +43,12 @@ typedef void (*hal_timer_irq_handler_t)(void);
 /* Maximum timer frequency */
 #define NRF5340_MAX_TIMER_FREQ    (16000000)
 
+#if MYNEWT_VAL_CHOICE(MCU_LFCLK_SOURCE, LFXO)
+#define LFCLK_FREQ              (MYNEWT_VAL(MCU_LFXO_FREQ))
+#else
+#define LFCLK_FREQ              (32768) /* Hz */
+#endif
+
 struct nrf5340_hal_timer {
     uint8_t tmr_enabled;
     uint8_t tmr_irq_num;
@@ -539,8 +545,8 @@ hal_timer_config(int timer_num, uint32_t freq_hz)
 
 #if (MYNEWT_VAL(TIMER_3) || MYNEWT_VAL(TIMER_4))
     if ((timer_num == 3) || (timer_num == 4)) {
-        /* NOTE: we only allow the RTC frequency to be set at 32768 */
-        if (bsptimer->tmr_enabled || (freq_hz != 32768) ||
+        /* NOTE: we only allow the RTC frequency to be set at LFCLK freq */
+        if (bsptimer->tmr_enabled || (freq_hz != LFCLK_FREQ) ||
             (bsptimer->tmr_reg == NULL)) {
             rc = EINVAL;
             goto err;

hw/mcu/nordic/nrf5340_net/syscfg.yml

@@ -49,6 +49,11 @@ syscfg.defs:
             - LFXO      # 32.768 kHz crystal oscillator
             - LFSYNTH   # 32.768 kHz synthesized from HFCLK
 
+    MCU_LFXO_FREQ:
+        description: >
+            Frequency of LFXO oscillator.
+        value: 32768
+
     MCU_GPIO_USE_PORT_EVENT:
         description: >
             When enabled, hal_gpio will use GPIOTE PORT event instead of PIN