Teensy 3.2 -- Corrupted serial port values when run above 48MHz?

[Zane470]

Hello,

I'm trying to communicate with a Microchip LoRaWAN modem (RN2903) using a Teensy 3.2. It works well when using the code at the bottom.

The problem is that it only works when I set the CPU speed to 48MHz or slower. When I set it to 72 MHz the join function (ttn.join(appEui, appKey);) causes my program to reset over and over...not sure why this happens. I'm using a baudrate of 57600, which is standard for this modem.

Anyone have any ideas? This is the code for the library:

https://github.com/TheThingsNetwork/arduino-device-lib/blob/master/src/TheThingsNetwork.cpp

I tried stripping out all of the PROGMEM statements and changed each of the string functions to their original version (for example P_strcpy to strcpy) but that didn't solve the problem.

It seems like it is some issue with delays, but there are only a couple in that library and changing them doesn't seem to do anything + they are only used for the autobaud feature. Or it could be some issue relating to the fact that the library is written for AVR processors (which is why I tried removing all of the PROGMEM statements and the other calls related to them).

#include <TheThingsNetwork.h>

/* Serial debugging */
#define debugSerial Serial
#define DEBUG_SERIAL_BAUD 57600

/* LoraWAN */
const char *appEui = "70B3D57ED000BDDF";
const char *appKey = "6C19B3357B72BCC89F3C5170DAB71F99";
#define loraSerial Serial1
#define freqPlan TTN_FP_US915
#define LORA_SERIAL_BAUD 57600
TheThingsNetwork ttn(loraSerial, debugSerial, freqPlan);

void setup() 
{
  debugSerial.begin(DEBUG_SERIAL_BAUD);
  loraSerial.begin(LORA_SERIAL_BAUD);
  delay(2000);

  /* Reset modem */
  pinMode(21, OUTPUT);
  digitalWrite(21, LOW);  
  delay(1000);             
  digitalWrite(21, HIGH);  
  delay(1000);

  debugSerial.println("-- STATUS");
  ttn.showStatus();

  delay(2000);
  
  debugSerial.println("-- JOIN");
  ttn.join(appEui, appKey);
}

void loop() 
{
  delay(1000);
  
  int sensorValue = analogRead(A0);
  float voltage = sensorValue * (3.3 / 1023.0) * 6;
  Serial.println(voltage);
}

 

[Zane470]

Figured it out. It was a combination of two issues.

1.) I had to strip out all of the AVR related PROGMEM stuff from The Things Network library. It was causing all of the strings to be corrupted. A working version of the file can be found here: https://pastebin.com/gBdHCAMJ

2.) When the modem was switching on it was making my voltage regulator hit its current limit, causing everything to reset. Need to add a big capacitor or a regulator that can push more current I guess.