mimxrt/machine_i2c_target: Support I2C target mode.

The functionality is similar to the RP2 implementation.  The supported
address size is 7 bit.  In order to achieve a sufficient response, the
target I2C IRQ handler has to run from RAM, causing much more code moved to
RAM than required.

Tested with Teensy 4.1, MIMXRT1021EVK, MIMXRT1011EVK and MIMXRT1170, using
both a On-Board SoftI2C as controller and a RP2 Pico as external
controller.

Signed-off-by: Damien George <damien@micropython.org>
Signed-off-by: robert-hh <robert@hammelrath.com>

Author: robert-hh

ports/mimxrt/boards/common.ld

@@ -98,7 +98,7 @@ SECTIONS
   .text :
   {
     . = ALIGN(4);
-    *(EXCLUDE_FILE(*fsl_flexspi.o *gc.o *vm.o *parse*.o *runtime*.o *map.o *mpirq.o ) .text*) /* .text* sections (code) */
+    *(EXCLUDE_FILE(*fsl_flexspi.o *gc.o *vm.o *runtime*.o *map.o *mpirq.o *machine_i2c_target.o *fsl_lpi2c.o) .text*) /* .text* sections (code) */
     *(.rodata)               /* .rodata sections (constants, strings, etc.) */
     *(.rodata*)              /* .rodata* sections (constants, strings, etc.) */
     *(.glue_7)               /* glue arm to thumb code */

ports/mimxrt/machine_i2c.c

@@ -33,11 +33,7 @@
 
 #include "fsl_iomuxc.h"
 #include "fsl_lpi2c.h"
-
-#define DEFAULT_I2C_ID          (0)
-#define DEFAULT_I2C_FREQ        (400000)
-#define DEFAULT_I2C_DRIVE       (6)
-#define DEFAULT_I2C_TIMEOUT     (50000)
+#include "machine_i2c.h"
 
 typedef struct _machine_i2c_obj_t {
     mp_obj_base_t base;
@@ -57,12 +53,11 @@ typedef struct _iomux_table_t {
     uint32_t configRegister;
 } iomux_table_t;
 
-static const uint8_t i2c_index_table[] = MICROPY_HW_I2C_INDEX;
-static LPI2C_Type *i2c_base_ptr_table[] = LPI2C_BASE_PTRS;
+const uint8_t i2c_index_table[] = MICROPY_HW_I2C_INDEX;
+LPI2C_Type *i2c_base_ptr_table[] = LPI2C_BASE_PTRS;
+const uint8_t micropy_hw_i2c_num = MICROPY_HW_I2C_NUM;
 static const iomux_table_t iomux_table[] = { IOMUX_TABLE_I2C };
 
-#define MICROPY_HW_I2C_NUM     ARRAY_SIZE(i2c_index_table)
-
 #define SCL (iomux_table[index])
 #define SDA (iomux_table[index + 1])
 

ports/mimxrt/machine_i2c.h

@@ -0,0 +1,38 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2025 Damien P. George
+ * Copyright (c) 2025 Robert Hammelrath
+ *
+ * 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.
+ */
+
+#define DEFAULT_I2C_ID          (0)
+#define DEFAULT_I2C_FREQ        (400000)
+#define DEFAULT_I2C_DRIVE       (6)
+#define DEFAULT_I2C_TIMEOUT     (50000)
+#define DEFAULT_I2C_FILTER_NS   (200)
+#define MICROPY_HW_I2C_NUM      ARRAY_SIZE(i2c_index_table)
+
+extern const uint8_t i2c_index_table[];
+extern LPI2C_Type *i2c_base_ptr_table[];
+extern bool lpi2c_set_iomux(int8_t hw_i2c, uint8_t drive);
+extern const uint8_t micropy_hw_i2c_num;

ports/mimxrt/machine_i2c_target.c

@@ -0,0 +1,168 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2025 Damien P. George
+ * Copyright (c) 2025 Robert Hammelrath
+ *
+ * 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 "fsl_lpi2c.h"
+#include "machine_i2c.h"
+#include CLOCK_CONFIG_H
+
+typedef struct _machine_i2c_target_obj_t {
+    mp_obj_base_t base;
+    LPI2C_Type *i2c_inst;
+    uint8_t i2c_id;
+    uint8_t addr;
+    lpi2c_slave_config_t slave_config;
+    lpi2c_slave_handle_t handle;
+} machine_i2c_target_obj_t;
+
+static void lpi2c_slave_callback(LPI2C_Type *base, lpi2c_slave_transfer_t *xfer, void *param) {
+    machine_i2c_target_obj_t *self = (machine_i2c_target_obj_t *)param;
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[self->i2c_id];
+
+    switch (xfer->event) {
+        case kLPI2C_SlaveAddressMatchEvent:
+            // Controller addressed us.
+            machine_i2c_target_data_addr_match(data, xfer->receivedAddress & 1);
+            break;
+        case kLPI2C_SlaveReceiveEvent:
+            // Data from controller is available for reading.
+            machine_i2c_target_data_write_request(self, data);
+            break;
+        case kLPI2C_SlaveTransmitEvent:
+            // Controller is requesting data.
+            machine_i2c_target_data_read_request(self, data);
+            break;
+        case kLPI2C_SlaveCompletionEvent:
+            // Transfer done.
+            machine_i2c_target_data_stop(data);
+            break;
+        default:
+            break;
+    }
+}
+
+/******************************************************************************/
+// I2CTarget port implementation
+
+static inline size_t mp_machine_i2c_target_get_index(machine_i2c_target_obj_t *self) {
+    return self->i2c_id;
+}
+
+static inline void mp_machine_i2c_target_event_callback(machine_i2c_target_irq_obj_t *irq) {
+    mp_irq_handler(&irq->base);
+}
+
+static size_t mp_machine_i2c_target_read_bytes(machine_i2c_target_obj_t *self, size_t len, uint8_t *buf) {
+    // LPI2C_Type *i2c_inst = self->i2c_inst;
+    // mp_int_t i = 0;
+    // mp_int_t val = 0;
+    // while (i < len && !((val = i2c_inst->SRDR) & LPI2C_SRDR_RXEMPTY_MASK)) {
+    //     buf[i++] = (uint8_t)(val & 0xff);
+    // }
+    // return i;
+    // Simple and fast version for len == 1
+    buf[0] = (uint8_t)(self->i2c_inst->SRDR);
+    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->i2c_inst->STDR = 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_drive };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_id, MP_ARG_INT, {.u_int = DEFAULT_I2C_ID} },
+        { 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_OBJ, {.u_rom_obj = MP_ROM_NONE}},
+        { MP_QSTR_mem_addrsize, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} },
+        { MP_QSTR_drive, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = DEFAULT_I2C_DRIVE} },
+    };
+
+    // 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);
+
+    // Get I2C bus.
+    int i2c_id = args[ARG_id].u_int;
+    if (i2c_id < 0 || i2c_id >= micropy_hw_i2c_num || i2c_index_table[i2c_id] == 0) {
+        mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("I2C(%d) doesn't exist"), i2c_id);
+    }
+    int i2c_hw_id = i2c_index_table[i2c_id]; // the hw i2c number 1..n
+
+    // Get I2C Object.
+    machine_i2c_target_obj_t *self = mp_obj_malloc_with_finaliser(machine_i2c_target_obj_t, &machine_i2c_target_type);
+    self->i2c_id = i2c_id;
+    self->i2c_inst = i2c_base_ptr_table[i2c_hw_id];
+    uint8_t drive = args[ARG_drive].u_int;
+    if (drive < 1 || drive > 7) {
+        drive = DEFAULT_I2C_DRIVE;
+    }
+    // Set the target address.
+    self->addr = args[ARG_addr].u_int;
+    // Initialise data.
+    MP_STATE_PORT(machine_i2c_target_mem_obj)[i2c_id] = args[ARG_mem].u_obj;
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[self->i2c_id];
+    machine_i2c_target_data_init(data, args[ARG_mem].u_obj, args[ARG_mem_addrsize].u_int);
+
+    // Initialise the GPIO pins
+    lpi2c_set_iomux(i2c_hw_id, drive);
+    // Initialise the I2C peripheral
+    LPI2C_SlaveGetDefaultConfig(&self->slave_config);
+    self->slave_config.address0 = self->addr;
+    self->slave_config.sdaGlitchFilterWidth_ns = DEFAULT_I2C_FILTER_NS;
+    self->slave_config.sclGlitchFilterWidth_ns = DEFAULT_I2C_FILTER_NS;
+    LPI2C_SlaveInit(self->i2c_inst, &self->slave_config, BOARD_BOOTCLOCKRUN_LPI2C_CLK_ROOT);
+    // Create the LPI2C handle for the non-blocking transfer
+    LPI2C_SlaveTransferCreateHandle(self->i2c_inst, &self->handle, lpi2c_slave_callback, self);
+    // Start accepting I2C transfers on the LPI2C slave peripheral
+    status_t reVal = LPI2C_SlaveTransferNonBlocking(self->i2c_inst, &self->handle,
+        kLPI2C_SlaveAddressMatchEvent | kLPI2C_SlaveTransmitEvent | kLPI2C_SlaveReceiveEvent | kLPI2C_SlaveCompletionEvent);
+    if (reVal != kStatus_Success) {
+        mp_raise_ValueError(MP_ERROR_TEXT("cannot start I2C"));
+    }
+    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(%u, addr=%u)", self->i2c_id, self->addr);
+}
+
+// Stop the Slave transfer and free the memory objects.
+static void mp_machine_i2c_target_deinit(machine_i2c_target_obj_t *self) {
+    LPI2C_SlaveDeinit(self->i2c_inst);
+}

ports/mimxrt/main.c

@@ -55,6 +55,7 @@
 #endif
 
 #include "systick.h"
+#include "extmod/modmachine.h"
 #include "extmod/modnetwork.h"
 #include "extmod/vfs.h"
 

ports/mimxrt/mpconfigport.h

@@ -92,6 +92,11 @@ uint32_t trng_random_u32(void);
 #define MICROPY_PY_MACHINE_PWM              (1)
 #define MICROPY_PY_MACHINE_PWM_INCLUDEFILE  "ports/mimxrt/machine_pwm.c"
 #define MICROPY_PY_MACHINE_I2C              (1)
+#define MICROPY_PY_MACHINE_I2C_TARGET       (1)
+#define MICROPY_PY_MACHINE_I2C_TARGET_INCLUDEFILE "ports/mimxrt/machine_i2c_target.c"
+#define MICROPY_PY_MACHINE_I2C_TARGET_MAX   (FSL_FEATURE_SOC_LPI2C_COUNT)
+#define MICROPY_PY_MACHINE_I2C_TARGET_HARD_IRQ (1)
+#define MICROPY_PY_MACHINE_I2C_TARGET_FINALISER (1)
 #ifndef MICROPY_PY_MACHINE_I2S
 #define MICROPY_PY_MACHINE_I2S              (0)
 #endif