MicroPython port to qemu

This is experimental, community-supported port for Cortex-M and RISC-V RV32IMC emulation as provided by QEMU (http://qemu.org).

The purposes of this port are to enable:

Continuous integration
- run tests against architecture-specific parts of code base
Experimentation
- simulation & prototyping of anything that has architecture-specific code
- exploring instruction set in terms of optimising some part of MicroPython or a module
Streamlined debugging
- no need for JTAG or even an MCU chip itself
- no need to use OpenOCD or anything else that might slow down the process in terms of plugging things together, pressing buttons, etc.

Dependencies

ARM

For ARM-based boards the build requires a bare-metal ARM toolchain, such as arm-none-eabi-gcc.

RISC-V

For RISC-V-based boards the build requires a bare metal RISC-V toolchain with GCC 10 or later, either with multilib support or 32 bits specific (M, C, and Zicsr extensions must be supported, along with ilp32 ABI). Both newlib and picolibc are supported, with the latter having precedence if found.

Most pre-built toolchains should work out of the box, either coming from your Linux distribution's package manager, or independently packaged ones like xPack.

Build instructions

First make sure the MicroPython cross-compiler is built (run from this directory):

$ make -C ../../mpy-cross

Then build using:

$ make

The default qemu-supported board is mps2-an385, a Cortex-M3 board. To select a different board pass the BOARD argument to make, for example:

$ make BOARD=SABRELITE

Available boards are:

Name for `BOARD=`	Architecture	Corresponding qemu board
`MICROBIT`	`arm`	`microbit`
`MPS2_AN385`	`arm`	`mps2-an385`
`NETDUINO2`	`arm`	`netduino2`
`SABRELITE`	`arm`	`sabrelite`
`VIRT_RV32`	`riscv32`	`virt`

Running

When the firmware is run it will provide a REPL on the emulated hardware UART. To access the REPL directly use:

$ make repl

This will start qemu-system-arm with the UART redirected to stdio. It's also possible to redirect the UART to a pty device using:

$ make run

This will start the emulation and the name of the pty device will be printed to stdout. This serial device then be accessed via a serial terminal program, for example mpremote:

$ mpremote connect /dev/pts/1

You can disconnect and reconnect to the serial device multiple times. Once you are finished, stop the make run command by pressing Ctrl-C where that command was started (or execute machine.reset() at the REPL).

The test suite can be run against the firmware by using the UART redirection. You can either do this automatically using the single command:

$ make test

Or manually by first starting the emulation with make run and then running the tests against the serial device, for example:

$ cd ../../tests
$ ./run-tests.py -t /dev/pts/1

Extra make options

The following options can be specified on the make command line:

CFLAGS_EXTRA: pass in extra flags for the compiler.
RUN_TESTS_EXTRA: pass in extra flags for run-tests.py when invoked via make test.
QEMU_DEBUG=1: when running qemu (via repl, run or test target), qemu will block until a debugger is connected. By default it waits for a gdb connection on TCP port 1234.
QEMU_DEBUG_ARGS: defaults to -s (gdb on TCP port 1234), but can be overridden with different qemu gdb arguments.
QEMU_DEBUG_EXTRA: extra options to pass to qemu when QEMU_DEBUG=1 is used.