nRF52840: Add E.getVDDH() method to get VDDH voltage

Courtesy of @fanoush

Author: gfwilliams

ChangeLog

@@ -3,6 +3,7 @@
             Bangle.js: Fix wrapString when wrapping a non-UTF8 string containing UTF8 characters (fix #2633) 
             Ensure jshPushIOCharEvent is more stable when the FIFO is full
             Bangle.js: g.findFont now attempts to use Intl:2 if there's room. Also fix memory leak
+            nRF52840: Add E.getVDDH() method to get VDDH voltage
 
      2v26 : nRF5x: ensure TIMER1_IRQHandler doesn't always wake idle loop up (fix #1900)
             Puck.js: On v2.1 ensure Puck.mag behaves like other variants - just returning the last reading (avoids glitches when used with Puck.magOn)

src/jshardware.h

@@ -388,6 +388,8 @@ JsVarFloat jshReadTemperature();
 
 /// The voltage that a reading of 1 from `analogRead` actually represents, in volts
 JsVarFloat jshReadVRef();
+/// On nRF52833/40 this is the VDDH value (before the internal voltage regulator)
+JsVarFloat jshReadVDDH();
 
 /** Get a random number - either using special purpose hardware or by
  * reading noise from an analog input. If unimplemented, this should

src/jswrap_espruino.c

@@ -182,6 +182,22 @@ While this is implemented on Espruino boards, it may not be implemented on other
 devices. If so it'll return NaN.
  */
 
+/*JSON{
+  "type" : "staticmethod",
+  "#if" : "defined(NRF52833) || defined(NRF52840)",
+  "class" : "E",
+  "name" : "getVDDH",
+  "generate_full" : "jshReadVDDH()",
+  "return" : ["float","The voltage on VDDH input"]
+}
+Return the voltage on VDDH input
+
+**Note:** This value is calculated by reading the voltage on an internal
+voltage reference with the ADC. It will be slightly noisy, so if you need this
+for accurate measurements we'd recommend that you call this function several
+times and average the results.
+ */
+
 
 int nativeCallGetCType() {
   if (lex->tk == LEX_R_VOID) {

targets/nrf5x/jshardware.c

@@ -2857,43 +2857,47 @@ JsVarFloat jshReadTemperature() {
 #endif
 }
 
-// The voltage that a reading of 1 from `analogRead` actually represents
-JsVarFloat jshReadVRef() {
 #ifdef NRF52_SERIES
+nrf_saadc_value_t jshReadVDD(nrf_saadc_input_t pin, nrf_saadc_acqtime_t time, nrf_saadc_gain_t gain) {
   nrf_saadc_channel_config_t config;
-  config.acq_time = NRF_SAADC_ACQTIME_3US;
-  config.gain = NRF_SAADC_GAIN1_6; // 1/6 of input volts
+  config.acq_time = time;
+  config.gain = gain; 
   config.mode = NRF_SAADC_MODE_SINGLE_ENDED;
-
-#ifdef ESPR_VREF_VDDH
-  config.pin_p = 0x0D; // Not in Nordic's libs, but this is VDDHDIV5 - we probably want to be looking at VDDH
-  config.pin_n = 0x0D;
-#else
-  config.pin_p = NRF_SAADC_INPUT_VDD;
-  config.pin_n = NRF_SAADC_INPUT_VDD;
-#endif
+  config.pin_p = pin;
+  config.pin_n = pin;
   config.reference = NRF_SAADC_REFERENCE_INTERNAL; // 0.6v reference.
   config.resistor_p = NRF_SAADC_RESISTOR_DISABLED;
   config.resistor_n = NRF_SAADC_RESISTOR_DISABLED;
 
   bool adcInUse = nrf_analog_read_start();
 
   // make reading
-  JsVarFloat f;
+  nrf_saadc_value_t f;
   do {
     nrf_analog_read_interrupted = false;
     nrf_saadc_enable();
     nrf_saadc_resolution_set(NRF_SAADC_RESOLUTION_14BIT);
     nrf_saadc_channel_init(0, &config);
 
-    f = nrf_analog_read() * (6.0 * 0.6 / 16384.0);
+    f = nrf_analog_read();
   } while (nrf_analog_read_interrupted);
   nrf_analog_read_end(adcInUse);
-#ifdef ESPR_VREF_VDDH
-  f *= 5; // we were on VDDHDIV5
+  return f;
+}
 #endif
 
-  return f;
+#if defined(NRF52833) || defined(NRF52840)
+JsVarFloat jshReadVDDH() {
+    return jshReadVDD(0x0D, NRF_SAADC_ACQTIME_20US, NRF_SAADC_GAIN1_2) // When using VDDHDIV5 as input, the acquisition time must be 10 µs or longer.
+    *(2.0 * 5.0 * 0.6 / 16384.0); // gain 1/2, VDDHDIV5, 0.6v reference, 2^14 = 1.0 
+}
+#endif
+
+// The voltage that a reading of 1 from `analogRead` actually represents
+JsVarFloat jshReadVRef() {
+#ifdef NRF52_SERIES
+  return jshReadVDD(NRF_SAADC_INPUT_VDD, NRF_SAADC_ACQTIME_3US, NRF_SAADC_GAIN1_6)
+    *(6.0 * 0.6 / 16384.0); // gain 1/6, 0.6v reference, 2^14 = 1.0) 
 #else
   const nrf_adc_config_t nrf_adc_config =  {
        NRF_ADC_CONFIG_RES_10BIT,