439298be15
This commit prevents the device from "hanging" when using lightsleep while the WiFi chip is active. Whenever the WiFi chip wants to interrupt the microcontroller to notify it for a new package, it sets the CYW43_PIN_WL_HOST_WAKE pin to high, triggering an IRQ. However, as polling the chip cannot happen in an interrupt handler, it subsequently notifies the pendsv-service to do a poll as soon as the interrupt handler ended. In order to prevent a new interrupt from happening immediately afterwards, even before the poll has run, the IRQ handler disables interrupts from the pin. The first problem occurs, when a WiFi package arrives while the main loop is in cyw43-code. In order to prevent concurrent access of the hardware, the network code blocks pendsv from running again while entering lwIP code. The same holds for direct cyw43 code (like changing the cyw43-gpios, i.e. the LED on the Pico W). While the pendsv is disabled, interrupts can still occur to schedule a poll (and disable further interrupts), but it will not run. This can happen while the microcontroller is anywhere in rp2040 code. In order to preserve power while waiting for cyw43 responses, cyw43_configport.h defines CYW43_DO_IOCTL_WAIT and CYW43_SDPCM_SEND_COMMON_WAIT to __WFI(). While this might work in most cases, there are 2 edge cases where it fails: - When an interrupt has already been received by the cyw43 stack, for example due to an incoming ethernet packet. - When the interrupt from the cyw43 response comes before the microcontroller entered the __WFI() instruction. When that happens, wfi will just block forever as no further interrupts are received. The only way to safely use wfi to wake up from an interrupt is inside a critical section, as this delays interrupts until the wfi is entered, possibly resuming immediately until interrupts are reenabled and the interrupt handler is run. Additionally this critical section needs to check whether the interrupt has already been disabled and pendsv was triggered, as in such a case, wfi can never be woken up, and needs to be skipped, because there is already a package from the network chip waiting. Note that this turns cyw43_yield into a nop (and thereby the cyw43-loops into busy waits) from the second time onwards, as after the first call, a pendsv request will definitely be pending. More logic could be added, to explicitly enable the interrupt in this case. Regarding lightsleep, this code has a similar problem. When an interrupt occurs during lightsleep, the IRQ and pendsv handler and thereby poll are run immediately, with the clocks still disabled, causing the SPI transfers to fail. If we don't want to add complex logic inside the IRQ handler we need to protect the whole lightsleep procedure form interrupts with a critical section, exiting out early if an interrupt is pending for whatever reason. Only then we can start to shut down clocks and only enable interrupts when the system is ready again. Other interrupt handlers might also be happy, that they are only run when the system is fully operational. Tested on a Pico W, calling machine.lightsleep() within an endless loop and pinging from the outside.
The RP2 port
This is a port of MicroPython to the Raspberry Pi RP2 series of microcontrollers. Currently supported features are:
- REPL over USB VCP, and optionally over UART (on GP0/GP1).
- Filesystem on the internal flash, using littlefs2.
- Support for native code generation and inline assembler.
utimemodule with sleep, time and ticks functions.uosmodule with VFS support.machinemodule with the following classes:Pin,ADC,PWM,I2C,SPI,SoftI2C,SoftSPI,Timer,UART,WDT.rp2module with programmable IO (PIO) support.
See the examples/rp2/ directory for some example code.
Building
The MicroPython cross-compiler must be built first, which will be used to pre-compile (freeze) built-in Python code. This cross-compiler is built and run on the host machine using:
$ make -C mpy-cross
This command should be executed from the root directory of this repository. All other commands below should be executed from the ports/rp2/ directory.
Building of the RP2 firmware is done entirely using CMake, although a simple Makefile is also provided as a convenience. To build the firmware run (from this directory):
$ make submodules
$ make clean
$ make
You can also build the standard CMake way. The final firmware is found in
the top-level of the CMake build directory (build by default) and is
called firmware.uf2.
If you are using a different board other than a Rasoberry Pi Pico, then you should pass the board name to the build; e.g. for Raspberry Pi Pico W:
$ make BOARD=PICO_W submodules
$ make BOARD=PICO_W clean
$ make BOARD=PICO_W
Deploying firmware to the device
Firmware can be deployed to the device by putting it into bootloader mode
(hold down BOOTSEL while powering on or resetting) and then copying
firmware.uf2 to the USB mass storage device that appears.
If MicroPython is already installed then the bootloader can be entered by
executing import machine; machine.bootloader() at the REPL.
Sample code
The following samples can be easily run on the board by entering paste mode with Ctrl-E at the REPL, then cut-and-pasting the sample code to the REPL, then executing the code with Ctrl-D.
Blinky
This blinks the on-board LED on the Pico board at 1.25Hz, using a Timer object with a callback.
from machine import Pin, Timer
led = Pin(25, Pin.OUT)
tim = Timer()
def tick(timer):
global led
led.toggle()
tim.init(freq=2.5, mode=Timer.PERIODIC, callback=tick)
PIO blinky
This blinks the on-board LED on the Pico board at 1Hz, using a PIO peripheral and PIO assembler to directly toggle the LED at the required rate.
from machine import Pin
import rp2
@rp2.asm_pio(set_init=rp2.PIO.OUT_LOW)
def blink_1hz():
# Turn on the LED and delay, taking 1000 cycles.
set(pins, 1)
set(x, 31) [6]
label("delay_high")
nop() [29]
jmp(x_dec, "delay_high")
# Turn off the LED and delay, taking 1000 cycles.
set(pins, 0)
set(x, 31) [6]
label("delay_low")
nop() [29]
jmp(x_dec, "delay_low")
# Create StateMachine(0) with the blink_1hz program, outputting on Pin(25).
sm = rp2.StateMachine(0, blink_1hz, freq=2000, set_base=Pin(25))
sm.active(1)
See the examples/rp2/ directory for further example code.