zephyr/machine_i2c_target: Implement I2CTarget class.

Tested and working on rpi_pico and nucleo_wb55rg.

Signed-off-by: Damien George <damien@micropython.org>

ports/zephyr/boards/nucleo_wb55rg.conf

@@ -4,6 +4,7 @@ CONFIG_NETWORKING=n
 CONFIG_FLASH=y
 CONFIG_FLASH_MAP=y
 CONFIG_I2C=y
+CONFIG_I2C_TARGET=y
 CONFIG_SPI=y
 
 # Bluetooth

ports/zephyr/boards/rpi_pico.conf

@@ -13,6 +13,7 @@ CONFIG_NETWORKING=n
 CONFIG_FLASH=y
 CONFIG_FLASH_MAP=y
 CONFIG_I2C=y
+CONFIG_I2C_TARGET=y
 CONFIG_SPI=y
 
 # MicroPython config.

ports/zephyr/machine_i2c_target.c

@@ -0,0 +1,191 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2025 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+// This file is never compiled standalone, it's included directly from
+// extmod/machine_i2c_target.c via MICROPY_PY_MACHINE_I2C_TARGET_INCLUDEFILE.
+
+#include <zephyr/drivers/i2c.h>
+
+#include "zephyr_device.h"
+
+typedef struct _machine_i2c_target_obj_t {
+    mp_obj_base_t base;
+    const struct device *dev;
+    struct i2c_target_config cfg;
+    uint8_t state;
+    uint8_t data_byte;
+} machine_i2c_target_obj_t;
+
+static machine_i2c_target_obj_t machine_i2c_target_obj[] = {
+    {.base = {&machine_i2c_target_type}, .dev = NULL},
+};
+
+/******************************************************************************/
+// zephyr bindings
+//
+// Note that it's possible to get callbacks in either of these sequences:
+// - read_requested read_processed read_processed ... (eg STM32)
+// - read_requested read_processed read_requested read_processed ... (eg RP2xxx / Design Ware)
+
+static int i2c_target_write_requested(struct i2c_target_config *config) {
+    machine_i2c_target_obj_t *self = CONTAINER_OF(config, machine_i2c_target_obj_t, cfg);
+    self->state = STATE_WRITING;
+    machine_i2c_target_data_addr_match(&machine_i2c_target_data[0], false);
+    return 0;
+}
+
+static int i2c_target_write_received(struct i2c_target_config *config, uint8_t val) {
+    machine_i2c_target_obj_t *self = CONTAINER_OF(config, machine_i2c_target_obj_t, cfg);
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[0];
+    self->data_byte = val;
+    machine_i2c_target_data_write_request(self, data);
+    return 0;
+}
+
+static int i2c_target_read_requested(struct i2c_target_config *config, uint8_t *val) {
+    machine_i2c_target_obj_t *self = CONTAINER_OF(config, machine_i2c_target_obj_t, cfg);
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[0];
+    if (self->state != STATE_READING) {
+        machine_i2c_target_data_addr_match(data, true);
+        machine_i2c_target_data_read_request(self, data);
+        self->state = STATE_READING;
+    }
+    *val = self->data_byte;
+    return 0;
+}
+
+static int i2c_target_read_processed(struct i2c_target_config *config, uint8_t *val) {
+    machine_i2c_target_obj_t *self = CONTAINER_OF(config, machine_i2c_target_obj_t, cfg);
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[0];
+    machine_i2c_target_data_read_request(self, data);
+    *val = self->data_byte;
+    return 0;
+}
+
+// called only on stop, not restart
+static int i2c_target_stop(struct i2c_target_config *config) {
+    machine_i2c_target_obj_t *self = CONTAINER_OF(config, machine_i2c_target_obj_t, cfg);
+    if (self->state == STATE_IDLE) {
+        // Assume a stop without a start is a 0-byte write.
+        machine_i2c_target_data_addr_match(&machine_i2c_target_data[0], false);
+    }
+    self->state = STATE_IDLE;
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[0];
+    machine_i2c_target_data_stop(data);
+    return 0;
+}
+
+static struct i2c_target_callbacks i2c_target_callbacks = {
+    .write_requested = i2c_target_write_requested,
+    .read_requested = i2c_target_read_requested,
+    .write_received = i2c_target_write_received,
+    .read_processed = i2c_target_read_processed,
+    .stop = i2c_target_stop,
+};
+
+/******************************************************************************/
+// I2CTarget port implementation
+
+static inline size_t mp_machine_i2c_target_get_index(machine_i2c_target_obj_t *self) {
+    return 0;
+}
+
+static void mp_machine_i2c_target_event_callback(machine_i2c_target_irq_obj_t *irq) {
+    char dummy;
+    void *orig_top = MP_STATE_THREAD(stack_top);
+    mp_uint_t orig_limit = MP_STATE_THREAD(stack_limit);
+    MP_STATE_THREAD(stack_top) = &dummy;
+    MP_STATE_THREAD(stack_limit) = CONFIG_ISR_STACK_SIZE - 512;
+    mp_irq_handler(&irq->base);
+    MP_STATE_THREAD(stack_top) = orig_top;
+    MP_STATE_THREAD(stack_limit) = orig_limit;
+}
+
+static size_t mp_machine_i2c_target_read_bytes(machine_i2c_target_obj_t *self, size_t len, uint8_t *buf) {
+    buf[0] = self->data_byte;
+    return 1;
+}
+
+static size_t mp_machine_i2c_target_write_bytes(machine_i2c_target_obj_t *self, size_t len, const uint8_t *buf) {
+    self->data_byte = buf[0];
+    return 1;
+}
+
+static inline void mp_machine_i2c_target_irq_config(machine_i2c_target_obj_t *self, unsigned int trigger) {
+    (void)self;
+    (void)trigger;
+}
+
+static mp_obj_t mp_machine_i2c_target_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
+    enum { ARG_id, ARG_addr, ARG_addrsize, ARG_mem, ARG_mem_addrsize, ARG_scl, ARG_sda };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_id, MP_ARG_REQUIRED | MP_ARG_OBJ },
+        { MP_QSTR_addr, MP_ARG_REQUIRED | MP_ARG_INT },
+        { MP_QSTR_addrsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 7} },
+        { MP_QSTR_mem, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
+        { MP_QSTR_mem_addrsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} },
+    };
+
+    // Parse arguments.
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all_kw_array(n_args, n_kw, all_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    const struct device *dev = zephyr_device_find(args[ARG_id].u_obj);
+
+    machine_i2c_target_obj_t *self = &machine_i2c_target_obj[0];
+    if (!(self->dev == NULL || self->dev == dev)) {
+        mp_raise_ValueError(MP_ERROR_TEXT("only one I2CTarget supported"));
+    }
+    self->dev = dev;
+    self->cfg.flags = 0;
+    self->cfg.address = args[ARG_addr].u_int;
+    self->cfg.callbacks = &i2c_target_callbacks;
+
+    // Initialise data.
+    self->state = STATE_IDLE;
+    MP_STATE_PORT(machine_i2c_target_mem_obj)[0] = args[ARG_mem].u_obj;
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[0];
+    machine_i2c_target_data_init(data, args[ARG_mem].u_obj, args[ARG_mem_addrsize].u_int);
+
+    // Initialise the I2C target.
+    int ret = i2c_target_register(self->dev, &self->cfg);
+    if (ret < 0) {
+        mp_raise_OSError(-ret);
+    }
+
+    return MP_OBJ_FROM_PTR(self);
+}
+
+static void mp_machine_i2c_target_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
+    machine_i2c_target_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_printf(print, "I2CTarget(%s, addr=%u)",
+        self->dev == NULL ? "" : self->dev->name, self->cfg.address);
+}
+
+static void mp_machine_i2c_target_deinit(machine_i2c_target_obj_t *self) {
+    i2c_target_unregister(self->dev, &self->cfg);
+    self->dev = NULL;
+}

ports/zephyr/main.c

@@ -53,6 +53,7 @@
 #include "shared/runtime/pyexec.h"
 #include "shared/readline/readline.h"
 #include "extmod/modbluetooth.h"
+#include "extmod/modmachine.h"
 
 #if MICROPY_VFS
 #include "extmod/vfs.h"
@@ -197,6 +198,9 @@ soft_reset_exit:
     #if MICROPY_PY_MACHINE
     machine_pin_deinit();
     #endif
+    #if MICROPY_PY_MACHINE_I2C_TARGET
+    mp_machine_i2c_target_deinit_all();
+    #endif
 
     #if MICROPY_PY_THREAD
     mp_thread_deinit();

ports/zephyr/mpconfigport.h

@@ -62,6 +62,12 @@
 #define MICROPY_PY_MACHINE          (1)
 #define MICROPY_PY_MACHINE_INCLUDEFILE "ports/zephyr/modmachine.c"
 #define MICROPY_PY_MACHINE_I2C      (1)
+#ifdef CONFIG_I2C_TARGET
+#define MICROPY_PY_MACHINE_I2C_TARGET (1)
+#define MICROPY_PY_MACHINE_I2C_TARGET_INCLUDEFILE "ports/zephyr/machine_i2c_target.c"
+#define MICROPY_PY_MACHINE_I2C_TARGET_MAX (1)
+#define MICROPY_PY_MACHINE_I2C_TARGET_HARD_IRQ (1)
+#endif
 #define MICROPY_PY_MACHINE_SOFTI2C  (1)
 #define MICROPY_PY_MACHINE_SPI      (1)
 #define MICROPY_PY_MACHINE_SPI_MSB (SPI_TRANSFER_MSB)