Using Adafruit RFM9x module

[lukecyca]

I'm using a regular ESP32 along with this RFM9x module.

https://learn.adafruit.com/adafruit-rfm69hcw-and-rfm96-rfm95-rfm98-lora-packet-padio-breakouts/pinouts#spi-logic-pins-2-6

I've hooked it up such that the pins are connected to the following pins on the module:

#define TTN_SPI_HOST      HSPI_HOST
#define TTN_SPI_DMA_CHAN  1
#define TTN_PIN_SPI_SCLK  [SCK]
#define TTN_PIN_SPI_MOSI  [MOSI]
#define TTN_PIN_SPI_MISO  [MISO]
#define TTN_PIN_NSS       [CS]
#define TTN_PIN_RXTX      TTN_NOT_CONNECTED
#define TTN_PIN_RST       [RST]
#define TTN_PIN_DIO0      [G0]
#define TTN_PIN_DIO1      [G1]

However, it fails at radio.c:739. I instrumented the code and found that the RegVersion returned is 0x9 (0b1001) instead of the expected 0x12 (0b10010). Given the similar-but-shifted binary representations, I suspect a timing/sync problem on the bus.

Any ideas?

[manuelbl]

I agree with your analysis: It seems to be SPI related and it's likely a timing issue and not a wiring issue (otherwise 0xff would be returned).

I propose you experiment with the SPI parameters. In hal_spi_init() in hal_esp32.c you can make the following changes:

• Add the cs_ena_posttrans line (see below). It has helped in a previous project.
• Or change the mode to 1, 2 or 3

The relevant code is:

spi_device_interface_config_t spi_device_intf_config = {
    .mode = 0,
    .clock_speed_hz = CONFIG_TTN_SPI_FREQ,
    .command_bits = 0,
    .address_bits = 8,
    .spics_io_num = lmic_pins.nss,
    .queue_size = SPI_QUEUE_SIZE,
    .cs_ena_posttrans = 2
};

Do you happen to have a DSO? If so, try to capture the SPI communication and attach it to the issue. It would be very helpful.

[lukecyca]

Thanks - mode = 1 worked!

[manuelbl]

It's a bit surprising that mode = 1 works. The datasheet clearly specifies mode 0.

Today I've tested it with a RFM95W module (the green module on your Adafruit board) and did't have any problems with the unmodified software.

Most likely, the level converter / buffer chip on the Adafruit board change the timing. So I've ordered the Adafruit board and will test it myself. I'll try to find a setup that works with as many boards as possible.

[manuelbl]

In the mean time, I've changed the SPI mode to 1 (see 5cd2c7b) even though the SX1276 data sheet clearly states the SPI mode to be CPOL = 0 and CPHA = 0 (equivalent to mode 0).

However, another boards revealed the same problem with a particular pin configuration. Changing to mode 1 fixed it as well. I have now received the Adafruit breakout board it works with mode 1 as you have already discovered. Furthermore, it works with all other boards I have.