Cannot get BLE module to initialize

Question

I designed and had manufactured a custom version of the Arduino Nano IoT 33 (basically the same, except it has some additional ICs on the PCB). It is working just fine when I program using the Arduino language (e.g. I can get LEDs to light up, PWM output, etc.). The Nina W102 Bluetooth Low Energy module (BLE), however, will not initialize.

I get a failure code returned to me when I run BLE.begin() (the result is 0, meaning a failure code). I used a debugger to follow the stack trace, and found that the exact function where it fails is here (in HCI.cpp in the ArduinoBLE module):

int HCIClass::reset()
{
  return sendCommand(OGF_HOST_CTL << 10 | OCF_RESET);
}

I've reached the limits of my understanding of Arduino and BLE (I'm a little new to this), and don't understand what this code does and whether it's a clue to determine what I have set up wrong.

Some additional comments:

• I have triple checked my circuit schematics and board design. The schematics reflect nearly exactly the Arduino schematic here. https://store.arduino.cc/usa/nano-33-iot (see "PDF schematic"). I say "nearly" because I did not include the ECC608 Crypto Auth module and the LSDM6DS3TR IMU module (I assumed these are not relevant to successful BLE functionality - are they?)
• The BLE.begin() is in my setup() function and there's nothing else in the app. The rest of setup() is empty and the loop() function is empty as well.

-- UPDATE --

I was told that I probably need to update the firmware for the NINA W102 BLE module itself (assuming that's the cause of the problem in my original question), so I followed the instructions here: https://www.arduino.cc/en/Tutorial/WiFiNINA-FirmwareUpdater (WifiNina 1.5.0 library installed - the latest). Every time I hit "Update Firmware" (see screenshot), I get an error message, "Programmer Not Responding. Make sure that FirmwareUpdater sketch is loaded on the board." even though I have successfully loaded the sketch. (Also by the way, I have the latest version of Arduino IDE (1.8.13)).

To dig deeper, I uploaded the sketch via a debugger, and found that it is stuck in this loop of the FirmwareUpdater sketch:

if (!ESP32BootROM.begin(921600)) {
    Serial.println("Unable to communicate with ESP32 boot ROM!");
    while (1);
  }

The closest available solution on the internet to this problem is here https://forum.arduino.cc/index.php?topic=654833.0 and it did not work for me (still receive the same error, and I think that solution is outdated anyway).

Answer 1

The ArduinoBLE library resets the esp32 NINA firmware to BLE mode (default mode is WiFi). But this reset is in ifdefs for specific boards and uses the specific pins to signal BLE mode and for reset of the esp32.

For Nano 33 IoT this pins are 24 (SPI SS) for signal and 27 for reset.

The communication with NINA firmware in BLE mode is over UART named SerialHCI on pins 22 to 25 on Nano 33 IoT.