Test code for Raspberry Pi Pico W WiFi chip
Something somewhere behaves differently between the Raspberry Pi Pico talking to an external CYW4343W chip and trying to access the on-board CYW43439 chip on the Pico W.
When I request the chip ID from the external Infineon WiFi module, all is well: I get the results I expect. But when I try to get the chip ID from the on-board CYW43439 on the Pico W, I get garbage.
The Pico SDK includes code to work successfully with the on-board CYW43439 on the Pico W. The picowi code (described below) works with both the Pico W and a plain Pico with the external CYW4343W. I was even able to hack the Zephyr spi_bitbang driver to work in 3-wire mode, and that works. But when I try to use the Zephyr PIO SPI driver for the Pico and Pico W, it works correctly on the Pico but not on the Pico W (he whined).
The goal is to support the Zephyr Infineon WiFi driver on the Pico W: zephyr/drivers/wifi/infineon and modules/hal/infineon/wifi-host-driver The challenge is that the way to Pico W is built, the CYW43439 can only be accessed using 3 SPI lines, CS, CLK, and a bidirectional Data line on hard-wired GPIO lines. So the only way to get that result is to use the PIO feature of the RP2040 SOC. To support this, I wrote a PIO-based SPI driver for the Pico, already part of Zephyr: zephyr/drivers/spi/spi_rpi_pico_pio.c
An issue working with the Pico W is there's no practical way to access the traces on the board to connect, for example, a logic analyzer for monitoring the SPI bus. Jeremy Bentham built a stand-alone WiFi driver that works for both the Pico and Pico W: https://iosoft.blog/2022/12/06/picowi/ He got around the lack of access to the bus by wiring an external module (based on the CYW4343W) to a vanilla Pico. Since I thought that was a pretty good idea, I did the same thing to work on the PIO- based SPI driver. I wired a MuRata 1DX module as described for my testing.
This test program requires my development fork of Zephyr, which has changes required to use an SPI bus with the Infineon driver. The source URL is: https://github.com/ThreeEights/zephyr/tree/airoc-wifi-spi which should take you right to the airoc-wifi-spi branch in my repository.
With that branch of Zephyr checked out, this demo application can be built in the usual way. For the Pico with the external module, the build command is:
west build -p auto -b rpi_pico -- -DCMAKE_BUILD_TYPE=Debug
and for the Pico W:
west build -p auto -b rpi_pico/rp2040/w -- -DCMAKE_BUILD_TYPE=Debug
As in Jeremy Bentham's Web page, wire the external module (noting that the "WI-FI" and "BLUETOOTH" labels on the module connectors ARE BACKWARDS!!), selecting suitable Pico GPIOs for CS, CLK, DATA (SIO), WIFI_ON, and HOST_WAKE. As you can see in the boards/rpi_pico.overlay file, I used:
| Use | GPIO |
|---|---|
| CS | 13 |
| CLK | 14 |
| SIO | 15 |
| REG_ON | 16 |
| HOST_WAKE | 15 |
(Note that HOST_WAKE, which the WiFi chip uses to notify the CPU with and interrupt, needs to be the same as the data/SIO line.) The clock and data/SIO lines must also be assigned to the PIO in the pinctrl section.
Nothing special should be required for the Pico W; the pin assignments are hard-wired and shown in the boards/rpi_pico_rp2040_w.overlay file.
One curiosity of the Infineon WiFi chips is that they start up in a
peculiar byte ordering mode: out of a 4-byte (32-bit) command or
response, the data order is byte 2, 3, 0, then 1. The TEST_READ
command is hard-coded in this byte order (the actual data is
0x4000A004). The expected value of 0xFEEDBEAD should be returned
as 0xBEADFEED. The first attempt to read that register normally
results in an invalid pattern; subsequent attempts should return
the expected result.
Using the vanilla Raspberry Pi Pico with the external muRata WiFi module, the correct data is returned on the second request:
checkWiFi() called
Set data line low - pin 15
WIFI_NODE=WIFI_NODE
On pin=16
Sleep 150 msec
*** Booting Zephyr OS build v3.7.0-275-gccb616c96733 ***
Turn on WiFi chip
Add a delay of 50 msec
Request chip ID
Chip ID=0x06 0x06 0x06 0x06
Add a delay of 50 msec
Request chip ID
Chip ID=0xBE 0xAD 0xFE 0xED
Add a delay of 50 msec
Request chip ID
Chip ID=0xBE 0xAD 0xFE 0xED
Add a delay of 50 msec
Request chip ID
Chip ID=0xBE 0xAD 0xFE 0xED
Turn WiFi off
However, on the Pico W, I get garbage:
checkWiFi() called
Set data line low - pin 24
WIFI_NODE=WIFI_NODE
On pin=23
Sleep 150 msec
*** Booting Zephyr OS build v3.7.0-275-gccb616c96733 ***
Turn on WiFi chip
Add a delay of 50 msec
Request chip ID
Chip ID=0xFF 0xFF 0xD7 0xFF
Add a delay of 50 msec
Request chip ID
Chip ID=0xFF 0xFF 0x5F 0xFF
Add a delay of 50 msec
Request chip ID
Chip ID=0xFF 0xFF 0x5F 0xFF
Add a delay of 50 msec
Request chip ID
Chip ID=0xFF 0xFF 0x5F 0xFF
Turn WiFi off
(Though the garbage from the first request is different from the second and subsequent requests.)