kopia lustrzana https://github.com/micropython/micropython
306 wiersze
9.2 KiB
ReStructuredText
306 wiersze
9.2 KiB
ReStructuredText
.. _porting_to_a_board:
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Porting MicroPython
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===================
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The MicroPython project contains several ports to different microcontroller families and
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architectures. The project repository has a `ports <https://github.com/micropython/micropython/tree/master/ports>`_
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directory containing a subdirectory for each supported port.
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A port will typically contain definitions for multiple "boards", each of which is a specific piece of
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hardware that that port can run on, e.g. a development kit or device.
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The `minimal port <https://github.com/micropython/micropython/tree/master/ports/minimal>`_ is
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available as a simplified reference implementation of a MicroPython port. It can run on both the
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host system and an STM32F4xx MCU.
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In general, starting a port requires:
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- Setting up the toolchain (configuring Makefiles, etc).
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- Implementing boot configuration and CPU initialization.
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- Initialising basic drivers required for development and debugging (e.g. GPIO, UART).
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- Performing the board-specific configurations.
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- Implementing the port-specific modules.
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Minimal MicroPython firmware
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----------------------------
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The best way to start porting MicroPython to a new board is by integrating a minimal
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MicroPython interpreter. For this walkthrough, create a subdirectory for the new
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port in the ``ports`` directory:
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.. code-block:: bash
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$ cd ports
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$ mkdir example_port
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The basic MicroPython firmware is implemented in the main port file, e.g ``main.c``:
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.. code-block:: c
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#include "py/builtin.h"
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#include "py/compile.h"
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#include "py/gc.h"
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#include "py/mperrno.h"
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#include "py/stackctrl.h"
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#include "shared/runtime/gchelper.h"
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#include "shared/runtime/pyexec.h"
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// Allocate memory for the MicroPython GC heap.
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static char heap[4096];
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int main(int argc, char **argv) {
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// Initialise the MicroPython runtime.
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mp_stack_ctrl_init();
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gc_init(heap, heap + sizeof(heap));
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mp_init();
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// Start a normal REPL; will exit when ctrl-D is entered on a blank line.
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pyexec_friendly_repl();
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// Deinitialise the runtime.
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gc_sweep_all();
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mp_deinit();
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return 0;
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}
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// Handle uncaught exceptions (should never be reached in a correct C implementation).
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void nlr_jump_fail(void *val) {
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for (;;) {
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}
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}
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// Do a garbage collection cycle.
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void gc_collect(void) {
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gc_collect_start();
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gc_helper_collect_regs_and_stack();
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gc_collect_end();
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}
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// There is no filesystem so stat'ing returns nothing.
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mp_import_stat_t mp_import_stat(const char *path) {
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return MP_IMPORT_STAT_NO_EXIST;
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}
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// There is no filesystem so opening a file raises an exception.
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mp_lexer_t *mp_lexer_new_from_file(qstr filename) {
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mp_raise_OSError(MP_ENOENT);
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}
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We also need a Makefile at this point for the port:
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.. code-block:: Makefile
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# Include the core environment definitions; this will set $(TOP).
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include ../../py/mkenv.mk
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# Include py core make definitions.
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include $(TOP)/py/py.mk
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include $(TOP)/extmod/extmod.mk
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# Set CFLAGS and libraries.
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CFLAGS += -I. -I$(BUILD) -I$(TOP)
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LIBS += -lm
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# Define the required source files.
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SRC_C = \
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main.c \
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mphalport.c \
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shared/readline/readline.c \
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shared/runtime/gchelper_generic.c \
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shared/runtime/pyexec.c \
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shared/runtime/stdout_helpers.c \
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# Define source files containung qstrs.
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SRC_QSTR += shared/readline/readline.c shared/runtime/pyexec.c
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# Define the required object files.
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OBJ = $(PY_CORE_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
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# Define the top-level target, the main firmware.
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all: $(BUILD)/firmware.elf
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# Define how to build the firmware.
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$(BUILD)/firmware.elf: $(OBJ)
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$(ECHO) "LINK $@"
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$(Q)$(CC) $(LDFLAGS) -o $@ $^ $(LIBS)
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$(Q)$(SIZE) $@
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# Include remaining core make rules.
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include $(TOP)/py/mkrules.mk
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Remember to use proper tabs to indent the Makefile.
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MicroPython Configurations
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--------------------------
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After integrating the minimal code above, the next step is to create the MicroPython
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configuration files for the port. The compile-time configurations are specified in
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``mpconfigport.h`` and additional hardware-abstraction functions, such as time keeping,
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in ``mphalport.h``.
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The following is an example of an ``mpconfigport.h`` file:
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.. code-block:: c
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#include <stdint.h>
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// Python internal features.
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#define MICROPY_ENABLE_GC (1)
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#define MICROPY_HELPER_REPL (1)
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#define MICROPY_ERROR_REPORTING (MICROPY_ERROR_REPORTING_TERSE)
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#define MICROPY_FLOAT_IMPL (MICROPY_FLOAT_IMPL_FLOAT)
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// Fine control over Python builtins, classes, modules, etc.
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#define MICROPY_PY_ASYNC_AWAIT (0)
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#define MICROPY_PY_BUILTINS_SET (0)
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#define MICROPY_PY_ATTRTUPLE (0)
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#define MICROPY_PY_COLLECTIONS (0)
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#define MICROPY_PY_MATH (0)
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#define MICROPY_PY_IO (0)
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#define MICROPY_PY_STRUCT (0)
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// Type definitions for the specific machine.
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typedef intptr_t mp_int_t; // must be pointer size
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typedef uintptr_t mp_uint_t; // must be pointer size
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typedef long mp_off_t;
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// We need to provide a declaration/definition of alloca().
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#include <alloca.h>
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// Define the port's name and hardware.
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#define MICROPY_HW_BOARD_NAME "example-board"
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#define MICROPY_HW_MCU_NAME "unknown-cpu"
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#define MP_STATE_PORT MP_STATE_VM
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This configuration file contains machine-specific configurations including aspects like if different
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MicroPython features should be enabled e.g. ``#define MICROPY_ENABLE_GC (1)``. Making this Setting
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``(0)`` disables the feature.
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Other configurations include type definitions, root pointers, board name, microcontroller name
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etc.
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Similarly, an minimal example ``mphalport.h`` file looks like this:
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.. code-block:: c
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static inline void mp_hal_set_interrupt_char(char c) {}
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Support for standard input/output
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---------------------------------
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MicroPython requires at least a way to output characters, and to have a REPL it also
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requires a way to input characters. Functions for this can be implemented in the file
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``mphalport.c``, for example:
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.. code-block:: c
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#include <unistd.h>
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#include "py/mpconfig.h"
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// Receive single character, blocking until one is available.
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int mp_hal_stdin_rx_chr(void) {
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unsigned char c = 0;
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int r = read(STDIN_FILENO, &c, 1);
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(void)r;
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return c;
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}
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// Send the string of given length.
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void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
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int r = write(STDOUT_FILENO, str, len);
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(void)r;
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}
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These input and output functions have to be modified depending on the
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specific board API. This example uses the standard input/output stream.
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Building and running
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--------------------
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At this stage the directory of the new port should contain::
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ports/example_port/
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├── main.c
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├── Makefile
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├── mpconfigport.h
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├── mphalport.c
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└── mphalport.h
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The port can now be built by running ``make`` (or otherwise, depending on your system).
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If you are using the default compiler settings in the Makefile given above then this
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will create an executable called ``build/firmware.elf`` which can be executed directly.
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To get a functional REPL you may need to first configure the terminal to raw mode:
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.. code-block:: bash
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$ stty raw opost -echo
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$ ./build/firmware.elf
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That should give a MicroPython REPL. You can then run commands like:
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.. code-block:: bash
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MicroPython v1.13 on 2021-01-01; example-board with unknown-cpu
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>>> import sys
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>>> sys.implementation
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('micropython', (1, 13, 0))
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>>>
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Use Ctrl-D to exit, and then run ``reset`` to reset the terminal.
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Adding a module to the port
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---------------------------
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To add a custom module like ``myport``, first add the module definition in a file
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``modmyport.c``:
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.. code-block:: c
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#include "py/runtime.h"
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static mp_obj_t myport_info(void) {
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mp_printf(&mp_plat_print, "info about my port\n");
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return mp_const_none;
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}
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static MP_DEFINE_CONST_FUN_OBJ_0(myport_info_obj, myport_info);
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static const mp_rom_map_elem_t myport_module_globals_table[] = {
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{ MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR_myport) },
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{ MP_ROM_QSTR(MP_QSTR_info), MP_ROM_PTR(&myport_info_obj) },
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};
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static MP_DEFINE_CONST_DICT(myport_module_globals, myport_module_globals_table);
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const mp_obj_module_t myport_module = {
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.base = { &mp_type_module },
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.globals = (mp_obj_dict_t *)&myport_module_globals,
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};
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MP_REGISTER_MODULE(MP_QSTR_myport, myport_module);
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You will also need to edit the Makefile to add ``modmyport.c`` to the ``SRC_C`` list, and
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a new line adding the same file to ``SRC_QSTR`` (so qstrs are searched for in this new file),
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like this:
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.. code-block:: Makefile
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SRC_C = \
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main.c \
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modmyport.c \
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mphalport.c \
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...
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SRC_QSTR += modmyport.c
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If all went correctly then, after rebuilding, you should be able to import the new module:
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.. code-block:: bash
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>>> import myport
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>>> myport.info()
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info about my port
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>>>
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