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Experimenting with LoRa Backplate for PinePhone

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LoRa Backplate for PinePhone consists of...

  • Semtech SX1262 LoRa Transceiver (SPI) and antenna

    https://www.semtech.com/products/wireless-rf/lora-core/sx1262

  • I2C Connector that matches the I2C Port (Pogo Pins) on PinePhone

    https://wiki.pine64.org/index.php/PinePhone#Pogo_pins

  • I2C-To-SPI Bridge (ATtiny84) that connects the I2C Connector to the LoRa Transceiver (SPI)

    https://github.com/zschroeder6212/tiny-i2c-spi

Schematic: https://wiki.pine64.org/wiki/Pinedio#Pinephone_backplate

Let's probe the LoRa Backplate with a Bus Pirate, to transmit some SX1262 commands and read the responses: http://dangerousprototypes.com/docs/I2C

UPDATE: See these excellent articles by JF...

  • "First look at the LoRa backplate for the Pinephone"

  • "Flashing the LoRa backplate for the PinePhone"

  • "A driver for the LoRa backplate for the PinePhone"

I2C-To-SPI Bridge

Arduino Source Code: https://github.com/zschroeder6212/tiny-i2c-spi/blob/master/src/main.c

The bridge runs at I2C Address 0x28:

#include "USI_TWI_Slave.h"
#define I2C_ADDR 0x28

int main (void)
{   
    /* init I2C */
    usiTwiSlaveInit(I2C_ADDR);

    /* set received/requested callbacks */
    usi_onReceiverPtr = I2C_received;
    usi_onRequestPtr = I2C_requested;

The bridge transmits data to SPI when the first byte received is 0x01:

#define CMD_TRANSMIT    1
#define CMD_CONFIGURE   2

void I2C_received(uint8_t bytes_recieved)
{
    uint8_t command = usiTwiReceiveByte();

    switch(command)
    {
        case CMD_TRANSMIT:
        {
            CS_PORT &= ~(1<<CS);

            for(int i = 1; i < bytes_recieved; i++)
            {
                uint8_t received_byte = SPI_transfer(usiTwiReceiveByte());
                SPI_buffer[received_index++] = received_byte;

When the bridge receives a read command, it returns the bytes received from SPI:

void I2C_requested()
{
    usiTwiTransmitByte(SPI_buffer[transmit_index++]);
    if(transmit_index >= BUFFER_SIZE)
    {
        transmit_index = 0;
    }
}

usi functions are defined here: https://github.com/zschroeder6212/tiny-i2c-spi/blob/master/src/USI_TWI_Slave.c

Probe LoRa Backplate with Bus Pirate

Based on:

  • http://dangerousprototypes.com/docs/I2C

  • https://lupyuen.github.io/articles/i2c#appendix-test-bme280-with-bus-pirate

Connect Bus Pirate to LoRa Backplate:

Bus Pirate Pin Backplate Pin
MOSI SDA
CLK SCL
5V USB-5V
GND GND

Enter I2C mode, power on:

m
I2C > HW > 400
W

Scan I2C bus:

(1)

I2C scan results:

Searching I2C address space. Found devices at:
0x00 (0x00 W) 0x01 (0x00

or

Searching I2C address space. Found devices at:
0x40(0x20 W) 0x41(0x20

Problem: Bus Pirate hangs while scanning. And I2C Address of LoRa Backplate should be 0x28, not 0x00. Why?

Read I2C Address 0x28:

[0x51 r]

(Because 0x51 = 0x28 * 2 + 1)

Result:

I2C START BIT
WRITE: 0x51 ACK 
READ: 0x00 
NACK

Problem: Bus Pirate hangs while reading I2C Address 0x28 from LoRa Backplate. Why?

Read I2C Address 0x20:

[0x41 r]

(Because 0x41 = 0x20 * 2 + 1)

Same problem as above.

Read I2C Address 0x00:

[0x01 r]

(Because 0x01 = 0x00 * 2 + 1)

Same problem as above.

Same thing happens when we probe the Breakout Board for LoRa Backplate...

TODO: Write and Read I2C Address 0x28 Register 0x01:

[0x50 0x01 0x00] [0x51 r]

TODO: Write and Read I2C Address 0x00 Register 0x01?

[0x00 0x01 0x00] [0x01 r]

Test LoRa Backplate on PinePhone

On PinePhone with Manjaro Phosh, scanning I2C Bus 3 with i2cdetect:

[manjaro@manjaro-arm ~]$ sudo pacman -Syu i2c-tools

[manjaro@manjaro-arm ~]$ i2cdetect -l
i2c-0	unknown   	DesignWare HDMI                 	N/A
i2c-1	unknown   	mv64xxx_i2c adapter             	N/A
i2c-2	unknown   	mv64xxx_i2c adapter             	N/A
i2c-3	unknown   	mv64xxx_i2c adapter             	N/A
i2c-4	unknown   	i2c-csi                         	N/A
i2c-5	unknown   	i2c-2-mux (chan_id 0)           	N/A

[manjaro@manjaro-arm ~]$ sudo i2cdetect 3
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-3.
I will probe address range 0x08-0x77.
Continue? [Y/n]
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Problem: i2cdetect fails to detect the I2C Address (0x28) of the LoRa Backplate. Why?

Has the LoRa Backplate been flashed with the right firmware?

I2C-To-SPI Bridge on ATtiny84: https://github.com/zschroeder6212/tiny-i2c-spi

LoRa Backplate (I2C Address 0x28) doesn't appear when we scan I2C Buses 0 to 5:

[manjaro@manjaro-arm ~]$ sudo i2cdetect 0
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-0.
I will probe address range 0x08-0x77.
Continue? [Y/n]
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: 30 -- 32 -- -- 35 -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: 50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
[manjaro@manjaro-arm ~]$ sudo i2cdetect 1
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-1.
I will probe address range 0x08-0x77.
Continue? [Y/n]
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- UU -- -- -- UU -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- UU -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
[manjaro@manjaro-arm ~]$ sudo i2cdetect 2
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-2.
I will probe address range 0x08-0x77.
Continue? [Y/n]
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- UU --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
[manjaro@manjaro-arm ~]$ sudo i2cdetect 3
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-3.
I will probe address range 0x08-0x77.
Continue? [Y/n]
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
[manjaro@manjaro-arm ~]$ sudo i2cdetect 4
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-4.
I will probe address range 0x08-0x77.
Continue? [Y/n]
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
[manjaro@manjaro-arm ~]$ sudo i2cdetect 5
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-5.
I will probe address range 0x08-0x77.
Continue? [Y/n]
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- UU --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

(Nope it can't be I2C Bus 2 because we're expecting an entire bus dedicated for the I2C Pogo Pins)

Compare this with other PinePhone I2C devices:

https://github.com/jnavarro7/pineeye_for_pinephone

https://dev.to/pcvonz/i-c-on-the-pinephone-5090

UPDATE: See these excellent articles by JF...

  • "First look at the LoRa backplate for the Pinephone"

  • "Flashing the LoRa backplate for the PinePhone"

  • "A driver for the LoRa backplate for the PinePhone"

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