Fix power pulse & reset issue

examples/Tools/SerialSARAPassthrough/SerialSARAPassthrough.ino

@@ -10,29 +10,28 @@
    Circuit:
    - MKR NB 1500 board
    - Antenna
-   - 1500 mAh or higher lipo battery connected
    - SIM card
 
-   Make sure the Serial Monitor's line ending is set to "Both NL and CR"
+   Make sure the Serial Monitor's line ending is set to "Both NL and CR" or "Carriage Return"
 
-   create 11 December 2017
+   created 11 December 2017
    Sandeep Mistry
 */
 
 // baud rate used for both Serial ports
 unsigned long baud = 115200;
 
 void setup() {
-  // enable the POW_ON pin
-  pinMode(SARA_PWR_ON, OUTPUT);
-  digitalWrite(SARA_PWR_ON, HIGH);
-
-  // reset the ublox module
+  // NEVER EVER use RESET_N
   pinMode(SARA_RESETN, OUTPUT);
-  digitalWrite(SARA_RESETN, HIGH);
-  delay(100);
   digitalWrite(SARA_RESETN, LOW);
 
+  // Send Poweron pulse
+  pinMode(SARA_PWR_ON, OUTPUT);
+  digitalWrite(SARA_PWR_ON, HIGH);
+  delay(150);
+  digitalWrite(SARA_PWR_ON, LOW);
+
   Serial.begin(baud);
   SerialSARA.begin(baud);
 }

src/Modem.cpp

@@ -24,11 +24,12 @@
 ModemUrcHandler* ModemClass::_urcHandlers[MAX_URC_HANDLERS] = { NULL };
 Print* ModemClass::_debugPrint = NULL;
 
-ModemClass::ModemClass(Uart& uart, unsigned long baud, int resetPin, int powerOnPin) :
+ModemClass::ModemClass(Uart& uart, unsigned long baud, int resetPin, int powerOnPin, int vIntPin) :
   _uart(&uart),
   _baud(baud),
   _resetPin(resetPin),
   _powerOnPin(powerOnPin),
+  _vIntPin(vIntPin),
   _lastResponseOrUrcMillis(0),
   _atCommandState(AT_COMMAND_IDLE),
   _ready(1),
@@ -37,19 +38,42 @@ ModemClass::ModemClass(Uart& uart, unsigned long baud, int resetPin, int powerOn
   _buffer.reserve(64);
 }
 
+void ModemClass::setVIntPin(int vIntPin)
+{
+  // Allow setting only if unset, used to track state
+  if (_vIntPin==SARA_VINT_OFF || _vIntPin==SARA_VINT_ON) {
+    _vIntPin=vIntPin;
+  }
+}
+
+int ModemClass::isPowerOn()
+{
+  if (_vIntPin==SARA_VINT_OFF) {
+    return 0;
+  } else if (_vIntPin==SARA_VINT_ON) {
+    return 1;
+  }
+  return digitalRead(_vIntPin);
+}
+
 int ModemClass::begin(bool restart)
 {
+  // datasheet warns not to use _resetPin, this may lead to an unrecoverable state
+  digitalWrite(_resetPin, LOW);
+
+  if (restart) {
+    shutdown();
+    end();
+  }
+
   _uart->begin(_baud > 115200 ? 115200 : _baud);
 
   // power on module
-  pinMode(_powerOnPin, OUTPUT);
-  digitalWrite(_powerOnPin, HIGH);
-
-  if (_resetPin > -1 && restart) {
-    pinMode(_resetPin, OUTPUT);
-    digitalWrite(_resetPin, HIGH);
-    delay(100);
-    digitalWrite(_resetPin, LOW);
+  if (!isPowerOn()) {
+    digitalWrite(_powerOnPin, HIGH);
+    delay(150); // Datasheet says power-on pulse should be >=150ms, <=3200ms
+    digitalWrite(_powerOnPin, LOW);
+    setVIntPin(SARA_VINT_ON);
   } else {
     if (!autosense()) {
       return 0;
@@ -78,13 +102,29 @@ int ModemClass::begin(bool restart)
   return 1;
 }
 
+int ModemClass::shutdown()
+{
+  // AT command shutdown
+  if (isPowerOn()) {
+    send("AT+CPWROFF");
+    if (waitForResponse(40000) != 1) {
+      return 0;
+    }
+    setVIntPin(SARA_VINT_OFF);
+  }
+  return 1;
+}
+
 void ModemClass::end()
 {
   _uart->end();
-  digitalWrite(_resetPin, HIGH);
-
-  // power off module
-  digitalWrite(_powerOnPin, LOW);
+  // Hardware pin power off
+  if (isPowerOn()) {
+    digitalWrite(_powerOnPin, HIGH);
+    delay(1500); // Datasheet says power-off pulse should be >=1500ms
+    digitalWrite(_powerOnPin, LOW);
+    setVIntPin(SARA_VINT_OFF);
+  }
 }
 
 void ModemClass::debug()
@@ -340,4 +380,4 @@ void ModemClass::setBaudRate(unsigned long baud)
   _baud = baud;
 }
 
-ModemClass MODEM(SerialSARA, 115200, SARA_RESETN, SARA_PWR_ON);
+ModemClass MODEM(SerialSARA, 115200, SARA_RESETN, SARA_PWR_ON, SARA_VINT);

src/Modem.h

@@ -25,14 +25,26 @@
 
 #include <Arduino.h>
 
+/* The NB 1500 does not connect the SARA V_INT pin so that it can be monitored.
+   The below constants and associated code enables connecting SARA_VINT to a digital input
+   using a level shifter (1.8V to 5V) or simply a MOS transistor, say a 2N7000. 
+   The code does rudimentary tracking of the on/off state if this is not available.
+*/ 
+#define SARA_VINT_OFF (-1)
+#define SARA_VINT_ON  (-2)
+
+#ifndef SARA_VINT
+#define SARA_VINT SARA_VINT_OFF
+#endif
+
 class ModemUrcHandler {
 public:
   virtual void handleUrc(const String& urc) = 0;
 };
 
 class ModemClass {
 public:
-  ModemClass(Uart& uart, unsigned long baud, int resetPin, int powerOnPin);
+  ModemClass(Uart& uart, unsigned long baud, int resetPin, int powerOnPin, int vIntPin=SARA_VINT);
 
   int begin(bool restart = false);
   void end();
@@ -45,6 +57,9 @@ class ModemClass {
 
   int noop();
   int reset();
+  int shutdown();
+  int isPowerOn();
+  void setVIntPin(int vIntPin);
 
   size_t write(uint8_t c);
   size_t write(const uint8_t*, size_t);
@@ -69,6 +84,7 @@ class ModemClass {
   unsigned long _baud;
   int _resetPin;
   int _powerOnPin;
+  int _vIntPin;
   unsigned long _lastResponseOrUrcMillis;
 
   enum {

src/NB.cpp

@@ -124,17 +124,17 @@ int NB::isAccessAlive()
 
 bool NB::shutdown()
 {
-  if (_state == NB_READY) {
-    MODEM.send("AT+CPWROFF");
-    MODEM.waitForResponse(40000);
+  // Attempt AT command shutdown
+  if (_state == NB_READY && MODEM.shutdown()) {
+    _state = NB_OFF;
+    return true;
   }
-  MODEM.end();
-  _state = NB_OFF;
-  return true;
+  return false;
 }
 
 bool NB::secureShutdown()
 {
+  // Hardware power off
   MODEM.end();
   _state = NB_OFF;
   return true;

src/NBFileUtils.cpp

@@ -12,8 +12,7 @@ bool NBFileUtils::begin(const bool restart)
 {
     int status;
 
-    if (restart)
-        MODEM.begin();
+    MODEM.begin(restart);
 
     if (_debug) {
         MODEM.debug();