samd/machine_i2c_target: Support I2C target mode.

Supporting readfrom_mem*(). writeto_mem() and a set of IRQs.  Enabled by
default for SAMD51 devices and SAMD21 devices with external flash.

Tested with ItsyBitsy M4 and ItsyBitsy M0 with both on-board SoftI2C and a
RP2 Pico as controller.

Signed-off-by: Damien George <[email protected]>
Signed-off-by: robert-hh <[email protected]>

Author: robert-hh

ports/samd/boards/ADAFRUIT_NEOKEY_TRINKEY/mpconfigboard.h

@@ -8,6 +8,7 @@
 #define MICROPY_PY_MACHINE_SOFTI2C  (0)
 #define MICROPY_PY_MACHINE_SOFTSPI  (0)
 #define MICROPY_PY_MACHINE_I2C      (0)
+#define MICROPY_PY_MACHINE_I2C_TARGET (0)
 #define MICROPY_PY_MACHINE_SPI      (0)
 #define MICROPY_PY_MACHINE_UART     (0)
 #define MICROPY_PY_MACHINE_ADC      (0)

ports/samd/machine_i2c.c

@@ -29,13 +29,11 @@
 
 #if MICROPY_PY_MACHINE_I2C
 
-#include "py/mphal.h"
 #include "py/mperrno.h"
 #include "extmod/modmachine.h"
 #include "samd_soc.h"
 #include "pin_af.h"
 #include "genhdr/pins.h"
-#include "clock_config.h"
 
 #define DEFAULT_I2C_FREQ    (400000)
 #define RISETIME_NS         (200)
@@ -79,9 +77,9 @@ static void i2c_send_command(Sercom *i2c, uint8_t command) {
 }
 
 void common_i2c_irq_handler(int i2c_id) {
-    // handle Sercom I2C IRQ
+    // Handle Sercom I2C IRQ for controller mode.
     machine_i2c_obj_t *self = MP_STATE_PORT(sercom_table[i2c_id]);
-    // Handle IRQ
+
     if (self != NULL) {
         Sercom *i2c = self->instance;
         // For now, clear all interrupts
@@ -114,7 +112,8 @@ void common_i2c_irq_handler(int i2c_id) {
         } else { // On any error, e.g. ARBLOST or BUSERROR, stop the transmission
             self->len = 0;
             self->state = state_buserr;
-            i2c->I2CM.INTFLAG.reg |= SERCOM_I2CM_INTFLAG_ERROR;
+            i2c->I2CM.INTFLAG.reg = SERCOM_I2CM_INTFLAG_ERROR |
+                SERCOM_I2CM_INTFLAG_SB | SERCOM_I2CM_INTFLAG_MB;
         }
     }
 }
@@ -158,28 +157,19 @@ mp_obj_t machine_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     // Get the peripheral object.
     machine_i2c_obj_t *self = mp_obj_malloc(machine_i2c_obj_t, &machine_i2c_type);
     self->id = id;
-    self->instance = sercom_instance[self->id];
+    self->instance = sercom_instance[id];
 
     // Set SCL/SDA pins.
-    self->scl = mp_hal_get_pin_obj(args[ARG_scl].u_obj);
-    self->sda = mp_hal_get_pin_obj(args[ARG_sda].u_obj);
+    self->sda = pin_config_for_i2c(args[ARG_sda].u_obj, id, 0);
+    self->scl = pin_config_for_i2c(args[ARG_scl].u_obj, id, 1);
+    MP_STATE_PORT(sercom_table[id]) = self;
 
-    sercom_pad_config_t scl_pad_config = get_sercom_config(self->scl, self->id);
-    sercom_pad_config_t sda_pad_config = get_sercom_config(self->sda, self->id);
-    if (sda_pad_config.pad_nr != 0 || scl_pad_config.pad_nr != 1) {
-        mp_raise_ValueError(MP_ERROR_TEXT("invalid sda/scl pin"));
-    }
-    MP_STATE_PORT(sercom_table[self->id]) = self;
     self->freq = args[ARG_freq].u_int;
     // The unit for ARG_timeout is us, but the code uses ms.
     self->timeout = args[ARG_timeout].u_int / 1000;
 
-    // Configure the Pin mux.
-    mp_hal_set_pin_mux(self->scl, scl_pad_config.alt_fct);
-    mp_hal_set_pin_mux(self->sda, sda_pad_config.alt_fct);
-
     // Set up the clocks
-    enable_sercom_clock(self->id);
+    enable_sercom_clock(id);
 
     // Initialise the I2C peripheral
     Sercom *i2c = self->instance;
@@ -207,13 +197,13 @@ mp_obj_t machine_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     i2c->I2CM.BAUD.reg = baud;
 
     // Enable interrupts
-    sercom_register_irq(self->id, &common_i2c_irq_handler);
+    sercom_register_irq(id, &common_i2c_irq_handler);
     #if defined(MCU_SAMD21)
-    NVIC_EnableIRQ(SERCOM0_IRQn + self->id);
+    NVIC_EnableIRQ(SERCOM0_IRQn + id);
     #elif defined(MCU_SAMD51)
-    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * self->id); // MB interrupt
-    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * self->id + 1); // SB interrupt
-    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * self->id + 3); // ERROR interrupt
+    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * id); // MB interrupt
+    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * id + 1); // SB interrupt
+    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * id + 3); // ERROR interrupt
     #endif
 
     // Now enable I2C.

ports/samd/machine_i2c_target.c

@@ -0,0 +1,213 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020-2021 Damien P. George
+ * Copyright (c) 2022-2025 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.
+ */
+
+#include "py/runtime.h"
+#include "samd_soc.h"
+#include "pin_af.h"
+#include "genhdr/pins.h"
+
+#define TRANSMIT          (1)
+#define RECEIVE           (0)
+#define NACK_RECVD        (i2c->I2CS.STATUS.bit.RXNACK == 1)
+#define IRQ_AMATCH        (i2c->I2CS.INTFLAG.bit.AMATCH == 1)
+#define IRQ_DRDY          (i2c->I2CS.INTFLAG.bit.DRDY == 1)
+#define IRQ_STOP          (i2c->I2CS.INTFLAG.bit.PREC == 1)
+
+#define PREPARE_ACK       i2c->I2CS.CTRLB.bit.ACKACT = 0
+#define PREPARE_NACK      i2c->I2CS.CTRLB.bit.ACKACT = 1
+
+typedef struct _machine_i2c_target_obj_t {
+    mp_obj_base_t base;
+    Sercom *instance;
+    uint8_t id;
+    uint8_t scl;
+    uint8_t sda;
+    uint8_t addr;
+    uint8_t direction;
+} machine_i2c_target_obj_t;
+
+void common_i2c_target_irq_handler(int i2c_id) {
+    // Handle Sercom I2C IRQ for target memory mode.
+    machine_i2c_target_obj_t *self = MP_STATE_PORT(sercom_table[i2c_id]);
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[i2c_id];
+
+    if (self != NULL) {
+        Sercom *i2c = self->instance;
+
+        if (IRQ_AMATCH) {
+            // Address match.
+            self->direction = i2c->I2CS.STATUS.bit.DIR;
+            machine_i2c_target_data_addr_match(data, self->direction);
+            // Send ACK
+            i2c->I2CS.CTRLB.bit.CMD = 3;
+
+        } else if (IRQ_DRDY) {
+            // Data to be handled, depending in the direction
+            if (self->direction == TRANSMIT) {
+                machine_i2c_target_data_read_request(self, data);
+            } else {
+                machine_i2c_target_data_write_request(self, data);
+            }
+            // ACK will be sent in mp_machine_i2c_target_read_bytes/mp_machine_i2c_target_write_bytes.
+        } else if (IRQ_STOP) {
+            // Stop detected. Just reset the data machine.
+            machine_i2c_target_data_stop(data);
+            i2c->I2CS.INTFLAG.reg |= SERCOM_I2CS_INTFLAG_PREC;
+
+        } else { // On any error clear the interrupts and reset the data state.
+            machine_i2c_target_data_stop(data);
+            i2c->I2CS.INTFLAG.reg = SERCOM_I2CS_INTFLAG_ERROR | SERCOM_I2CS_INTFLAG_AMATCH |
+                SERCOM_I2CS_INTFLAG_DRDY | SERCOM_I2CS_INTFLAG_PREC;
+        }
+    }
+}
+
+/******************************************************************************/
+// I2CTarget port implementation
+
+static inline size_t mp_machine_i2c_target_get_index(machine_i2c_target_obj_t *self) {
+    return self->id;
+}
+
+static 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) {
+    Sercom *i2c = self->instance;
+    buf[0] = i2c->I2CS.DATA.reg;
+    i2c->I2CS.CTRLB.bit.CMD = 3; // send ACK
+    return 1;
+}
+
+static size_t mp_machine_i2c_target_write_bytes(machine_i2c_target_obj_t *self, size_t len, const uint8_t *buf) {
+    Sercom *i2c = self->instance;
+    i2c->I2CS.DATA.reg = buf[0];
+    i2c->I2CS.CTRLB.bit.CMD = 3; // send ACK
+    return 1;
+}
+
+static inline void mp_machine_i2c_target_irq_config(machine_i2c_target_obj_t *self, unsigned int trigger) {
+    (void)self;
+    (void)trigger;
+}
+
+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[] = {
+        #if MICROPY_HW_DEFAULT_I2C_ID < 0
+        { MP_QSTR_id, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = -1} },
+        #else
+        { MP_QSTR_id, MP_ARG_INT, {.u_int = MICROPY_HW_DEFAULT_I2C_ID} },
+        #endif
+        { 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} },
+        #if defined(pin_SCL) && defined(pin_SDA)
+        { MP_QSTR_scl, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = pin_SCL} },
+        { MP_QSTR_sda, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = pin_SDA} },
+        #else
+        { MP_QSTR_scl, MP_ARG_REQUIRED | MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
+        { MP_QSTR_sda, MP_ARG_REQUIRED | MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
+        #endif
+    };
+
+    // Parse args.
+    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 id = args[ARG_id].u_int;
+    if (id < 0 || id >= SERCOM_INST_NUM) {
+        mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("I2C(%d) doesn't exist"), id);
+    }
+
+    // Get the peripheral object.
+    machine_i2c_target_obj_t *self = mp_obj_malloc_with_finaliser(machine_i2c_target_obj_t, &machine_i2c_target_type);
+    self->id = id;
+    self->instance = sercom_instance[id];
+
+    // Set SCL/SDA pins.
+    self->sda = pin_config_for_i2c(args[ARG_sda].u_obj, id, 0);
+    self->scl = pin_config_for_i2c(args[ARG_scl].u_obj, id, 1);
+
+    MP_STATE_PORT(sercom_table[id]) = self;
+
+    // Get the address and initialise data.
+    self->addr = args[ARG_addr].u_int;
+    MP_STATE_PORT(machine_i2c_target_mem_obj)[id] = args[ARG_mem].u_obj;
+    machine_i2c_target_data_t *data = &machine_i2c_target_data[id];
+    machine_i2c_target_data_init(data, args[ARG_mem].u_obj, args[ARG_mem_addrsize].u_int);
+
+    // Set up the clocks
+    enable_sercom_clock(id);
+
+    // Initialise the I2C peripheral
+    Sercom *i2c = self->instance;
+    // Reset the device
+    i2c->I2CS.CTRLA.reg = SERCOM_I2CM_CTRLA_SWRST;
+    while (i2c->I2CS.SYNCBUSY.bit.SWRST == 1) {
+    }
+
+    // Set to slave mode, enable SCl timeout, set the address
+    i2c->I2CS.CTRLA.reg = SERCOM_I2CS_CTRLA_MODE(0x04)
+        | SERCOM_I2CS_CTRLA_SEXTTOEN | SERCOM_I2CS_CTRLA_LOWTOUTEN;
+    i2c->I2CS.ADDR.reg = self->addr << 1;
+
+    // Enable interrupts
+    sercom_register_irq(id, &common_i2c_target_irq_handler);
+    #if defined(MCU_SAMD21)
+    NVIC_EnableIRQ(SERCOM0_IRQn + id);
+    #elif defined(MCU_SAMD51)
+    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * id);
+    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * id + 1);
+    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * id + 2);
+    NVIC_EnableIRQ(SERCOM0_0_IRQn + 4 * id + 3);
+    #endif
+    i2c->I2CS.INTENSET.reg = SERCOM_I2CS_INTENSET_DRDY | SERCOM_I2CS_INTENSET_AMATCH |
+        SERCOM_I2CS_INTENSET_PREC | SERCOM_I2CS_INTENSET_ERROR;
+
+    // Now enable I2C.
+    sercom_enable(i2c, 1);
+
+    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, "I2C(%u, scl=\"%q\", sda=\"%q\", addr=%u)",
+        self->id, pin_find_by_id(self->scl)->name, pin_find_by_id(self->sda)->name,
+        self->addr);
+}
+
+// Stop the Slave transfer and free the memory objects.
+static void mp_machine_i2c_target_deinit(machine_i2c_target_obj_t *self) {
+    // Disable I2C
+    sercom_enable(self->instance, 0);
+    MP_STATE_PORT(sercom_table[self->id]) = NULL;
+}

ports/samd/main.c

@@ -30,6 +30,7 @@
 #include "py/mperrno.h"
 #include "py/mphal.h"
 #include "py/stackctrl.h"
+#include "extmod/modmachine.h"
 #include "shared/readline/readline.h"
 #include "shared/runtime/gchelper.h"
 #include "shared/runtime/pyexec.h"
@@ -101,7 +102,7 @@ void samd_main(void) {
         mp_usbd_deinit();
         #endif
         gc_sweep_all();
-        #if MICROPY_PY_MACHINE_I2C || MICROPY_PY_MACHINE_SPI || MICROPY_PY_MACHINE_UART
+        #if MICROPY_PY_MACHINE_I2C || MICROPY_PY_MACHINE_I2C_TARGET || MICROPY_PY_MACHINE_SPI || MICROPY_PY_MACHINE_UART
         sercom_deinit_all();
         #endif
         mp_deinit();

ports/samd/mcu/samd21/mpconfigmcu.h

@@ -78,6 +78,9 @@ unsigned long trng_random_u32(int delay);
 #ifndef MICROPY_PY_ONEWIRE
 #define MICROPY_PY_ONEWIRE              (SAMD21_EXTRA_FEATURES)
 #endif
+#ifndef MICROPY_PY_MACHINE_I2C_TARGET
+#define MICROPY_PY_MACHINE_I2C_TARGET   (SAMD21_EXTRA_FEATURES)
+#endif
 
 #ifndef MICROPY_PY_MACHINE_PIN_BOARD_CPU
 #define MICROPY_PY_MACHINE_PIN_BOARD_CPU (1)

ports/samd/mcu/samd51/mpconfigmcu.h

@@ -16,6 +16,9 @@
 #define MICROPY_PY_RANDOM_SEED_INIT_FUNC (trng_random_u32())
 unsigned long trng_random_u32(void);
 #define MICROPY_PY_MACHINE_UART_IRQ     (1)
+#ifndef MICROPY_PY_MACHINE_I2C_TARGET
+#define MICROPY_PY_MACHINE_I2C_TARGET   (1)
+#endif
 
 // fatfs configuration used in ffconf.h
 #define MICROPY_FATFS_ENABLE_LFN            (1)

ports/samd/mpconfigport.h

@@ -127,6 +127,10 @@
 #define MICROPY_PY_MACHINE_WDT_INCLUDEFILE  "ports/samd/machine_wdt.c"
 #define MICROPY_PY_MACHINE_WDT_TIMEOUT_MS   (1)
 #define MICROPY_PLATFORM_VERSION            "ASF4"
+#define MICROPY_PY_MACHINE_I2C_TARGET_INCLUDEFILE  "ports/samd/machine_i2c_target.c"
+#define MICROPY_PY_MACHINE_I2C_TARGET_MAX   (SERCOM_INST_NUM)
+#define MICROPY_PY_MACHINE_I2C_TARGET_HARD_IRQ (1)
+#define MICROPY_PY_MACHINE_I2C_TARGET_FINALISER (1)
 
 #define MP_STATE_PORT MP_STATE_VM
 

ports/samd/pin_af.c

@@ -161,3 +161,19 @@ pwm_config_t get_pwm_config(int pin_id, int wanted_dev, uint8_t device_status[])
 }
 
 #endif
+
+#if MICROPY_PY_MACHINE_I2C || MICROPY_PY_MACHINE_I2C_TARGET
+
+// Configure a I2C pin. Used by machine_i2c.c and machine_i2c_target.c.
+uint8_t pin_config_for_i2c(mp_obj_t pin_obj, uint8_t id, uint8_t pad_nr) {
+    uint8_t pin = mp_hal_get_pin_obj(pin_obj);
+    sercom_pad_config_t pad_config = get_sercom_config(pin, id);
+    if (pad_config.pad_nr != pad_nr) {
+        mp_raise_ValueError(MP_ERROR_TEXT("invalid sda/scl pin"));
+    }
+    // Configure the Pin mux.
+    mp_hal_set_pin_mux(pin, pad_config.alt_fct);
+    return pin;
+}
+
+#endif

ports/samd/pin_af.h

@@ -100,3 +100,5 @@ adc_config_t get_adc_config(int pin_id, int32_t flag);
 pwm_config_t get_pwm_config(int pin_id, int wanted_dev, uint8_t used_dev[]);
 const machine_pin_obj_t *pin_find_by_id(int pin_id);
 const machine_pin_obj_t *pin_find(mp_obj_t pin);
+
+uint8_t pin_config_for_i2c(mp_obj_t pin_obj, uint8_t id, uint8_t pad_nr);

ports/samd/samd_soc.c

@@ -122,7 +122,7 @@ void samd_init(void) {
     machine_rtc_start(false);
 }
 
-#if MICROPY_PY_MACHINE_I2C || MICROPY_PY_MACHINE_SPI || MICROPY_PY_MACHINE_UART
+#if MICROPY_PY_MACHINE_I2C || MICROPY_PY_MACHINE_I2C_TARGET || MICROPY_PY_MACHINE_SPI || MICROPY_PY_MACHINE_UART
 
 Sercom *sercom_instance[] = SERCOM_INSTS;
 MP_REGISTER_ROOT_POINTER(void *sercom_table[SERCOM_INST_NUM]);