fix(ppp): Make modem reset delay configurable

The delay required to reset Simcom modem modules varies significantly across
different models, even where they have otherwise identical AT command
sets.

Simcom A7672 was failing to reset with the default 200ms delay. Make the reset
delay configurable to allow customising this for a specific modem.
Default delay, if not specified is kept at 200ms.

libraries/PPP/examples/PPP_Basic/PPP_Basic.ino

@@ -4,14 +4,15 @@
 #define PPP_MODEM_PIN "0000"  // or NULL
 
 // WaveShare SIM7600 HW Flow Control
-#define PPP_MODEM_RST     25
-#define PPP_MODEM_RST_LOW false  //active HIGH
-#define PPP_MODEM_TX      21
-#define PPP_MODEM_RX      22
-#define PPP_MODEM_RTS     26
-#define PPP_MODEM_CTS     27
-#define PPP_MODEM_FC      ESP_MODEM_FLOW_CONTROL_HW
-#define PPP_MODEM_MODEL   PPP_MODEM_SIM7600
+#define PPP_MODEM_RST        25
+#define PPP_MODEM_RST_LOW    false  //active HIGH
+#define PPP_MODEM_RST_DELAY  200
+#define PPP_MODEM_TX         21
+#define PPP_MODEM_RX         22
+#define PPP_MODEM_RTS        26
+#define PPP_MODEM_CTS        27
+#define PPP_MODEM_FC         ESP_MODEM_FLOW_CONTROL_HW
+#define PPP_MODEM_MODEL      PPP_MODEM_SIM7600
 
 // SIM800 basic module with just TX,RX and RST
 // #define PPP_MODEM_RST     0
@@ -60,7 +61,7 @@ void setup() {
   // Configure the modem
   PPP.setApn(PPP_MODEM_APN);
   PPP.setPin(PPP_MODEM_PIN);
-  PPP.setResetPin(PPP_MODEM_RST, PPP_MODEM_RST_LOW);
+  PPP.setResetPin(PPP_MODEM_RST, PPP_MODEM_RST_LOW, PPP_MODEM_RST_DELAY);
   PPP.setPins(PPP_MODEM_TX, PPP_MODEM_RX, PPP_MODEM_RTS, PPP_MODEM_CTS, PPP_MODEM_FC);
 
   Serial.println("Starting the modem. It might take a while!");

libraries/PPP/src/PPP.cpp

@@ -141,8 +141,8 @@ esp_modem_dce_t *PPPClass::handle() const {
 }
 
 PPPClass::PPPClass()
-  : _dce(NULL), _pin_tx(-1), _pin_rx(-1), _pin_rts(-1), _pin_cts(-1), _flow_ctrl(ESP_MODEM_FLOW_CONTROL_NONE), _pin_rst(-1), _pin_rst_act_low(true), _pin(NULL),
-    _apn(NULL), _rx_buffer_size(4096), _tx_buffer_size(512), _mode(ESP_MODEM_MODE_COMMAND), _uart_num(UART_NUM_1) {}
+  : _dce(NULL), _pin_tx(-1), _pin_rx(-1), _pin_rts(-1), _pin_cts(-1), _flow_ctrl(ESP_MODEM_FLOW_CONTROL_NONE), _pin_rst(-1), _pin_rst_act_low(true),
+    _pin_rst_delay(200), _pin(NULL), _apn(NULL), _rx_buffer_size(4096), _tx_buffer_size(512), _mode(ESP_MODEM_MODE_COMMAND), _uart_num(UART_NUM_1) {}
 
 PPPClass::~PPPClass() {}
 
@@ -152,9 +152,10 @@ bool PPPClass::pppDetachBus(void *bus_pointer) {
   return true;
 }
 
-void PPPClass::setResetPin(int8_t rst, bool active_low) {
+void PPPClass::setResetPin(int8_t rst, bool active_low, int16_t reset_delay) {
   _pin_rst = digitalPinToGPIONumber(rst);
   _pin_rst_act_low = active_low;
+  _pin_rst_delay = reset_delay;
 }
 
 bool PPPClass::setPins(int8_t tx, int8_t rx, int8_t rts, int8_t cts, esp_modem_flow_ctrl_t flow_ctrl) {
@@ -285,7 +286,7 @@ bool PPPClass::begin(ppp_modem_model_t model, uint8_t uart_num, int baud_rate) {
     }
     perimanSetPinBusExtraType(_pin_rst, "PPP_MODEM_RST");
     digitalWrite(_pin_rst, !_pin_rst_act_low);
-    delay(200);
+    delay(_pin_rst_delay);
     digitalWrite(_pin_rst, _pin_rst_act_low);
     delay(100);
   }

libraries/PPP/src/PPP.h

@@ -36,7 +36,7 @@ class PPPClass : public NetworkInterface {
   bool setPins(int8_t tx, int8_t rx, int8_t rts = -1, int8_t cts = -1, esp_modem_flow_ctrl_t flow_ctrl = ESP_MODEM_FLOW_CONTROL_NONE);
 
   // Using the reset pin of the module ensures that proper communication can be achieved
-  void setResetPin(int8_t rst, bool active_low = true);
+  void setResetPin(int8_t rst, bool active_low = true, int16_t reset_delay = 200);
 
   // Modem DCE APIs
   int RSSI() const;
@@ -94,6 +94,7 @@ class PPPClass : public NetworkInterface {
   esp_modem_flow_ctrl_t _flow_ctrl;
   int8_t _pin_rst;
   bool _pin_rst_act_low;
+  int16_t _pin_rst_delay;
   const char *_pin;
   const char *_apn;
   int _rx_buffer_size;