Merge pull request #5746 from espressif/i2c-slave

I2C Slave Implementation

CMakeLists.txt

@@ -7,6 +7,7 @@ set(CORE_SRCS
   cores/esp32/esp32-hal-dac.c
   cores/esp32/esp32-hal-gpio.c
   cores/esp32/esp32-hal-i2c.c
+  cores/esp32/esp32-hal-i2c-slave.c
   cores/esp32/esp32-hal-ledc.c
   cores/esp32/esp32-hal-matrix.c
   cores/esp32/esp32-hal-misc.c

cores/esp32/esp32-hal-i2c-slave.c

+// Copyright 2015-2021 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <inttypes.h>
+#include <string.h>
+#include <math.h>
+
+#include "sdkconfig.h"
+#include "esp_attr.h"
+#include "rom/gpio.h"
+#include "soc/gpio_sig_map.h"
+#include "hal/gpio_types.h"
+#include "driver/gpio.h"
+#include "esp_err.h"
+
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "freertos/queue.h"
+#include "freertos/semphr.h"
+#include "freertos/ringbuf.h"
+
+#include "esp_intr_alloc.h"
+#include "driver/periph_ctrl.h"
+#include "soc/i2c_reg.h"
+#include "soc/i2c_struct.h"
+#include "hal/i2c_ll.h"
+#include "esp32-hal-log.h"
+#include "esp32-hal-i2c-slave.h"
+
+#define I2C_SLAVE_USE_RX_QUEUE 0 // 1: Queue, 0: RingBuffer
+
+#if SOC_I2C_NUM > 1
+#define I2C_SCL_IDX(p)  ((p==0)?I2CEXT0_SCL_OUT_IDX:((p==1)?I2CEXT1_SCL_OUT_IDX:0))
+#define I2C_SDA_IDX(p) ((p==0)?I2CEXT0_SDA_OUT_IDX:((p==1)?I2CEXT1_SDA_OUT_IDX:0))
+#else
+#define I2C_SCL_IDX(p)  I2CEXT0_SCL_OUT_IDX
+#define I2C_SDA_IDX(p) I2CEXT0_SDA_OUT_IDX
+#endif
+
+#if CONFIG_IDF_TARGET_ESP32
+    #define I2C_TXFIFO_WM_INT_ENA    I2C_TXFIFO_EMPTY_INT_ENA
+    #define I2C_RXFIFO_WM_INT_ENA     I2C_RXFIFO_FULL_INT_ENA
+#endif
+
+enum {
+    I2C_SLAVE_EVT_RX, I2C_SLAVE_EVT_TX
+};
+
+typedef struct i2c_slave_struct_t {
+    i2c_dev_t * dev;
+    uint8_t num;
+    int8_t sda;
+    int8_t scl;
+    i2c_slave_request_cb_t request_callback;
+    i2c_slave_receive_cb_t receive_callback;
+    void * arg;
+    intr_handle_t intr_handle;
+    TaskHandle_t task_handle;
+    xQueueHandle event_queue;
+#if I2C_SLAVE_USE_RX_QUEUE
+    xQueueHandle rx_queue;
+#else
+    RingbufHandle_t rx_ring_buf;
+#endif
+    xQueueHandle tx_queue;
+    uint32_t rx_data_count;
+#if !CONFIG_DISABLE_HAL_LOCKS
+    xSemaphoreHandle lock;
+#endif
+} i2c_slave_struct_t;
+
+typedef union {
+    struct {
+        uint32_t event : 2;
+        uint32_t stop : 1;
+        uint32_t param : 29;
+    };
+    uint32_t val;
+} i2c_slave_queue_event_t;
+
+static i2c_slave_struct_t _i2c_bus_array[SOC_I2C_NUM] = {
+    { &I2C0, 0, -1, -1, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, 0
+#if !CONFIG_DISABLE_HAL_LOCKS
+    , NULL
+#endif
+    },
+#if SOC_I2C_NUM > 1
+    { &I2C1, 1, -1, -1, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, 0
+#if !CONFIG_DISABLE_HAL_LOCKS
+    , NULL
+#endif
+    }
+#endif
+};
+
+#if CONFIG_DISABLE_HAL_LOCKS
+#define I2C_SLAVE_MUTEX_LOCK()
+#define I2C_SLAVE_MUTEX_UNLOCK()
+#else
+#define I2C_SLAVE_MUTEX_LOCK()    if(i2c->lock){xSemaphoreTake(i2c->lock, portMAX_DELAY);}
+#define I2C_SLAVE_MUTEX_UNLOCK()  if(i2c->lock){xSemaphoreGive(i2c->lock);}
+#endif
+
+//-------------------------------------- HAL_LL (Missing Functions) ------------------------------------------------
+typedef enum {
+    I2C_STRETCH_CAUSE_MASTER_READ,
+    I2C_STRETCH_CAUSE_TX_FIFO_EMPTY,
+    I2C_STRETCH_CAUSE_RX_FIFO_FULL,
+    I2C_STRETCH_CAUSE_MAX
+} i2c_stretch_cause_t;
+
+static inline i2c_stretch_cause_t i2c_ll_stretch_cause(i2c_dev_t *hw)
+{
+#if CONFIG_IDF_TARGET_ESP32C3
+    return hw->sr.stretch_cause;
+#elif CONFIG_IDF_TARGET_ESP32S2
+    return hw->status_reg.stretch_cause;
+#else
+    return I2C_STRETCH_CAUSE_MAX;
+#endif
+}
+
+static inline void i2c_ll_set_stretch(i2c_dev_t *hw, uint16_t time)
+{
+#ifndef CONFIG_IDF_TARGET_ESP32
+    typeof(hw->scl_stretch_conf) scl_stretch_conf;
+    scl_stretch_conf.val = 0;
+    scl_stretch_conf.slave_scl_stretch_en = (time > 0);
+    scl_stretch_conf.stretch_protect_num = time;
+    scl_stretch_conf.slave_scl_stretch_clr = 1;
+    hw->scl_stretch_conf.val = scl_stretch_conf.val;
+    if(time > 0){
+        //enable interrupt
+        hw->int_ena.val |= I2C_SLAVE_STRETCH_INT_ENA;
+    } else {
+        //disable interrupt
+        hw->int_ena.val &= (~I2C_SLAVE_STRETCH_INT_ENA);
+    }
+#endif
+}
+
+static inline void i2c_ll_stretch_clr(i2c_dev_t *hw)
+{
+#ifndef CONFIG_IDF_TARGET_ESP32
+    hw->scl_stretch_conf.slave_scl_stretch_clr = 1;
+#endif
+}
+
+static inline bool i2c_ll_slave_addressed(i2c_dev_t *hw)
+{
+#if CONFIG_IDF_TARGET_ESP32C3
+    return hw->sr.slave_addressed;
+#else
+    return hw->status_reg.slave_addressed;
+#endif
+}
+
+static inline bool i2c_ll_slave_rw(i2c_dev_t *hw)//not exposed by hal_ll
+{
+#if CONFIG_IDF_TARGET_ESP32C3
+    return hw->sr.slave_rw;
+#else
+    return hw->status_reg.slave_rw;
+#endif
+}
+
+//-------------------------------------- PRIVATE (Function Prototypes) ------------------------------------------------
+static void i2c_slave_free_resources(i2c_slave_struct_t * i2c);
+static void i2c_slave_delay_us(uint64_t us);
+static void i2c_slave_gpio_mode(int8_t pin, gpio_mode_t mode);
+static bool i2c_slave_check_line_state(int8_t sda, int8_t scl);
+static bool i2c_slave_attach_gpio(i2c_slave_struct_t * i2c, int8_t sda, int8_t scl);
+static bool i2c_slave_detach_gpio(i2c_slave_struct_t * i2c);
+static bool i2c_slave_set_frequency(i2c_slave_struct_t * i2c, uint32_t clk_speed);
+static bool i2c_slave_send_event(i2c_slave_struct_t * i2c, i2c_slave_queue_event_t* event);
+static bool i2c_slave_handle_tx_fifo_empty(i2c_slave_struct_t * i2c);
+static bool i2c_slave_handle_rx_fifo_full(i2c_slave_struct_t * i2c, uint32_t len);
+static size_t i2c_slave_read_rx(i2c_slave_struct_t * i2c, uint8_t * data, size_t len);
+static void i2c_slave_isr_handler(void* arg);
+static void i2c_slave_task(void *pv_args);
+
+
+//=====================================================================================================================
+//-------------------------------------- Public Functions -------------------------------------------------------------
+//=====================================================================================================================
+
+esp_err_t i2cSlaveAttachCallbacks(uint8_t num, i2c_slave_request_cb_t request_callback, i2c_slave_receive_cb_t receive_callback, void * arg){
+    if(num >= SOC_I2C_NUM){
+        log_e("Invalid port num: %u", num);
+        return ESP_ERR_INVALID_ARG;
+    }
+    i2c_slave_struct_t * i2c = &_i2c_bus_array[num];
+    I2C_SLAVE_MUTEX_LOCK();
+    i2c->request_callback = request_callback;
+    i2c->receive_callback = receive_callback;
+    i2c->arg = arg;
+    I2C_SLAVE_MUTEX_UNLOCK();
+    return ESP_OK;
+}
+
+esp_err_t i2cSlaveInit(uint8_t num, int sda, int scl, uint16_t slaveID, uint32_t frequency, size_t rx_len, size_t tx_len) {
+    if(num >= SOC_I2C_NUM){
+        log_e("Invalid port num: %u", num);
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    if (sda < 0 || scl < 0) {
+        log_e("invalid pins sda=%d, scl=%d", sda, scl);
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    if(!frequency){
+        frequency = 100000;
+    } else if(frequency > 1000000){
+        frequency = 1000000;
+    }
+
+    log_i("Initialising I2C Slave: sda=%d scl=%d freq=%d, addr=0x%x", sda, scl, frequency, slaveID);
+
+    i2c_slave_struct_t * i2c = &_i2c_bus_array[num];
+    esp_err_t ret = ESP_OK;
+
+#if !CONFIG_DISABLE_HAL_LOCKS
+    if(!i2c->lock){
+        i2c->lock = xSemaphoreCreateMutex();
+        if (i2c->lock == NULL) {
+            log_e("RX queue create failed");
+            return ESP_ERR_NO_MEM;
+        }
+    }
+#endif
+
+    I2C_SLAVE_MUTEX_LOCK();
+    i2c_slave_free_resources(i2c);
+
+#if I2C_SLAVE_USE_RX_QUEUE
+    i2c->rx_queue = xQueueCreate(rx_len, sizeof(uint8_t));
+    if (i2c->rx_queue == NULL) {
+        log_e("RX queue create failed");
+        ret = ESP_ERR_NO_MEM;
+        goto fail;
+    }
+#else
+    i2c->rx_ring_buf = xRingbufferCreate(rx_len, RINGBUF_TYPE_BYTEBUF);
+    if (i2c->rx_ring_buf == NULL) {
+        log_e("RX RingBuf create failed");
+        ret = ESP_ERR_NO_MEM;
+        goto fail;
+    }
+#endif
+
+    i2c->tx_queue = xQueueCreate(tx_len, sizeof(uint8_t));
+    if (i2c->tx_queue == NULL) {
+        log_e("TX queue create failed");
+        ret = ESP_ERR_NO_MEM;
+        goto fail;
+    }
+
+    i2c->event_queue = xQueueCreate(16, sizeof(i2c_slave_queue_event_t));
+    if (i2c->event_queue == NULL) {
+        log_e("Event queue create failed");
+        ret = ESP_ERR_NO_MEM;
+        goto fail;
+    }
+
+    xTaskCreate(i2c_slave_task, "i2c_slave_task", 4096, i2c, 20, &i2c->task_handle);
+    if(i2c->task_handle == NULL){
+        log_e("Event thread create failed");
+        ret = ESP_ERR_NO_MEM;
+        goto fail;
+    }
+
+    if (frequency == 0) {
+        frequency = 100000L;
+    }
+    frequency = (frequency * 5) / 4;
+
+    if (i2c->num == 0) {
+        periph_module_enable(PERIPH_I2C0_MODULE);
+#if SOC_I2C_NUM > 1
+    } else {
+        periph_module_enable(PERIPH_I2C1_MODULE);
+#endif
+    }
+    
+    i2c_ll_slave_init(i2c->dev);
+    i2c_ll_set_fifo_mode(i2c->dev, true);
+    i2c_ll_set_slave_addr(i2c->dev, slaveID, false);
+    i2c_ll_set_tout(i2c->dev, 32000);
+    i2c_slave_set_frequency(i2c, frequency);
+
+    if (!i2c_slave_check_line_state(sda, scl)) {
+        log_e("bad pin state");
+        ret = ESP_FAIL;
+        goto fail;
+    }
+
+    i2c_slave_attach_gpio(i2c, sda, scl);
+
+    if (i2c_ll_is_bus_busy(i2c->dev)) {
+        log_w("Bus busy, reinit");
+        ret = ESP_FAIL;
+        goto fail;
+    }
+
+    i2c_ll_disable_intr_mask(i2c->dev, I2C_LL_INTR_MASK);
+    i2c_ll_clr_intsts_mask(i2c->dev, I2C_LL_INTR_MASK);
+    i2c_ll_set_fifo_mode(i2c->dev, true);
+
+    if (!i2c->intr_handle) {
+        uint32_t flags = ESP_INTR_FLAG_LOWMED | ESP_INTR_FLAG_SHARED;
+        if(i2c->num == 0) {
+            ret = esp_intr_alloc(ETS_I2C_EXT0_INTR_SOURCE, flags, &i2c_slave_isr_handler, i2c, &i2c->intr_handle);
+#if SOC_I2C_NUM > 1
+        } else {
+            ret = esp_intr_alloc(ETS_I2C_EXT1_INTR_SOURCE, flags, &i2c_slave_isr_handler, i2c, &i2c->intr_handle);
+#endif
+        }
+
+        if (ret != ESP_OK) {
+            log_e("install interrupt handler Failed=%d", ret);
+            goto fail;
+        }
+    }
+    
+    i2c_ll_txfifo_rst(i2c->dev);
+    i2c_ll_rxfifo_rst(i2c->dev);
+    i2c_ll_slave_enable_rx_it(i2c->dev);
+    i2c_ll_set_stretch(i2c->dev, 0x3FF);
+    i2c_ll_update(i2c->dev);
+    I2C_SLAVE_MUTEX_UNLOCK();
+    return ret;
+
+fail:
+    i2c_slave_free_resources(i2c);
+    I2C_SLAVE_MUTEX_UNLOCK();
+    return ret;
+}
+
+esp_err_t i2cSlaveDeinit(uint8_t num){
+    if(num >= SOC_I2C_NUM){
+        log_e("Invalid port num: %u", num);
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    i2c_slave_struct_t * i2c = &_i2c_bus_array[num];
+    if(!i2c->lock){
+        log_e("Lock is not initialized! Did you call i2c_slave_init()?");
+        return ESP_ERR_NO_MEM;
+    }
+    I2C_SLAVE_MUTEX_LOCK();
+    i2c_slave_free_resources(i2c);
+    I2C_SLAVE_MUTEX_UNLOCK();
+    return ESP_OK;
+}
+
+size_t i2cSlaveWrite(uint8_t num, const uint8_t *buf, uint32_t len, uint32_t timeout_ms) {
+    if(num >= SOC_I2C_NUM){
+        log_e("Invalid port num: %u", num);
+        return 0;
+    }
+    size_t to_queue = 0, to_fifo = 0;
+    i2c_slave_struct_t * i2c = &_i2c_bus_array[num];
+    if(!i2c->lock){
+        log_e("Lock is not initialized! Did you call i2c_slave_init()?");
+        return ESP_ERR_NO_MEM;
+    }
+    if(!i2c->tx_queue){
+        return 0;
+    }
+    I2C_SLAVE_MUTEX_LOCK();
+#if CONFIG_IDF_TARGET_ESP32
+    //make sure that tx is idle
+    uint64_t tout_at = esp_timer_get_time() + (timeout_ms * 1000);
+    while(i2c_ll_slave_addressed(i2c->dev) && i2c_ll_slave_rw(i2c->dev)) {
+        // ongoing MASTER READ
+        //wait up to timeout_ms for current transaction to finish
+        vTaskDelay(2);
+        if((uint64_t)esp_timer_get_time() >= tout_at){
+            log_e("TX IDLE WAIT TIMEOUT!");
+            I2C_SLAVE_MUTEX_UNLOCK();
+            return 0;
+        }
+    }
+    i2c_ll_slave_disable_tx_it(i2c->dev);
+    if (i2c_ll_get_txfifo_len(i2c->dev) < SOC_I2C_FIFO_LEN) {
+        i2c_ll_txfifo_rst(i2c->dev);
+    }
+#endif
+    to_fifo = i2c_ll_get_txfifo_len(i2c->dev);
+    if(len < to_fifo){
+        to_fifo = len;
+    }
+    i2c_ll_write_txfifo(i2c->dev, (uint8_t*)buf, to_fifo);
+    buf += to_fifo;
+    len -= to_fifo;
+    //reset tx_queue
+    xQueueReset(i2c->tx_queue);
+    //write the rest of the bytes to the queue
+    if(len){
+        to_queue = uxQueueSpacesAvailable(i2c->tx_queue);
+        if(len < to_queue){
+            to_queue = len;
+        }
+        for (size_t i = 0; i < to_queue; i++) {
+            if (xQueueSend(i2c->tx_queue, &buf[i], timeout_ms / portTICK_RATE_MS) != pdTRUE) {
+                xQueueReset(i2c->tx_queue);
+                to_queue = 0;
+                break;
+            }
+        }
+        //no need to enable TX_EMPTY if tx_queue is empty
+        if(to_queue){
+            i2c_ll_slave_enable_tx_it(i2c->dev);
+        }
+    }
+    I2C_SLAVE_MUTEX_UNLOCK();
+    return to_queue + to_fifo;
+}
+
+//=====================================================================================================================
+//-------------------------------------- Private Functions ------------------------------------------------------------
+//=====================================================================================================================
+
+static void i2c_slave_free_resources(i2c_slave_struct_t * i2c){
+    i2c_slave_detach_gpio(i2c);
+    i2c_ll_set_slave_addr(i2c->dev, 0, false);
+    i2c_ll_disable_intr_mask(i2c->dev, I2C_LL_INTR_MASK);
+    i2c_ll_clr_intsts_mask(i2c->dev, I2C_LL_INTR_MASK);
+
+    if (i2c->intr_handle) {
+        esp_intr_free(i2c->intr_handle);
+        i2c->intr_handle = NULL;
+    }
+
+    if(i2c->task_handle){
+        vTaskDelete(i2c->task_handle);
+        i2c->task_handle = NULL;
+    }
+
+#if I2C_SLAVE_USE_RX_QUEUE
+    if (i2c->rx_queue) {
+        vQueueDelete(i2c->rx_queue);
+        i2c->rx_queue = NULL;
+    }
+#else
+    if (i2c->rx_ring_buf) {
+        vRingbufferDelete(i2c->rx_ring_buf);
+        i2c->rx_ring_buf = NULL;
+    }
+#endif
+
+    if (i2c->tx_queue) {
+        vQueueDelete(i2c->tx_queue);
+        i2c->tx_queue = NULL;
+    }
+
+    if (i2c->event_queue) {
+        vQueueDelete(i2c->event_queue);
+        i2c->event_queue = NULL;
+    }
+
+    i2c->rx_data_count = 0;
+}
+
+static bool i2c_slave_set_frequency(i2c_slave_struct_t * i2c, uint32_t clk_speed)
+{
+    if (i2c == NULL) {
+        log_e("no control buffer");
+        return false;
+    }
+    if(clk_speed > 1100000UL){
+        clk_speed = 1100000UL;
+    }
+
+    // Adjust Fifo thresholds based on frequency
+    uint32_t a = (clk_speed / 50000L) + 2;
+    log_d("Fifo thresholds: rx_fifo_full = %d, tx_fifo_empty = %d", SOC_I2C_FIFO_LEN - a, a);
+
+    i2c_clk_cal_t clk_cal;
+#if SOC_I2C_SUPPORT_APB
+    i2c_ll_cal_bus_clk(APB_CLK_FREQ, clk_speed, &clk_cal);
+    i2c_ll_set_source_clk(i2c->dev, I2C_SCLK_APB);            /*!< I2C source clock from APB, 80M*/
+#elif SOC_I2C_SUPPORT_XTAL
+    i2c_ll_cal_bus_clk(XTAL_CLK_FREQ, clk_speed, &clk_cal);
+    i2c_ll_set_source_clk(i2c->dev, I2C_SCLK_XTAL);           /*!< I2C source clock from XTAL, 40M */
+#endif
+    i2c_ll_set_txfifo_empty_thr(i2c->dev, a);
+    i2c_ll_set_rxfifo_full_thr(i2c->dev, SOC_I2C_FIFO_LEN - a);
+    i2c_ll_set_bus_timing(i2c->dev, &clk_cal);
+    i2c_ll_set_filter(i2c->dev, 3);
+    return true;
+}
+
+static void i2c_slave_delay_us(uint64_t us)
+{
+    uint64_t m = esp_timer_get_time();
+    if (us) {
+        uint64_t e = (m + us);
+        if (m > e) { //overflow
+            while ((uint64_t)esp_timer_get_time() > e);
+        }
+        while ((uint64_t)esp_timer_get_time() < e);
+    }
+}
+
+static void i2c_slave_gpio_mode(int8_t pin, gpio_mode_t mode)
+{
+    gpio_config_t conf = {
+        .pin_bit_mask = 1LL << pin,
+        .mode = mode,
+        .pull_up_en = GPIO_PULLUP_ENABLE,
+        .pull_down_en = GPIO_PULLDOWN_DISABLE,
+        .intr_type = GPIO_INTR_DISABLE
+    };
+    gpio_config(&conf);
+}
+
+static bool i2c_slave_check_line_state(int8_t sda, int8_t scl)
+{
+    if (sda < 0 || scl < 0) {
+        return false;//return false since there is nothing to do
+    }
+    // if the bus is not 'clear' try the cycling SCL until SDA goes High or 9 cycles
+    gpio_set_level(sda, 1);
+    gpio_set_level(scl, 1);
+    i2c_slave_gpio_mode(sda, GPIO_MODE_INPUT | GPIO_MODE_DEF_OD);
+    i2c_slave_gpio_mode(scl, GPIO_MODE_INPUT | GPIO_MODE_DEF_OD);
+    gpio_set_level(scl, 1);
+
+    if (!gpio_get_level(sda) || !gpio_get_level(scl)) { // bus in busy state
+        log_w("invalid state sda(%d)=%d, scl(%d)=%d", sda, gpio_get_level(sda), scl, gpio_get_level(scl));
+        for (uint8_t a=0; a<9; a++) {
+            i2c_slave_delay_us(5);
+            if (gpio_get_level(sda) && gpio_get_level(scl)) { // bus recovered
+                log_w("Recovered after %d Cycles",a);
+                gpio_set_level(sda,0); // start
+                i2c_slave_delay_us(5);
+                for (uint8_t a=0;a<9; a++) {
+                    gpio_set_level(scl,1);
+                    i2c_slave_delay_us(5);
+                    gpio_set_level(scl,0);
+                    i2c_slave_delay_us(5);
+                }
+                gpio_set_level(scl,1);
+                i2c_slave_delay_us(5);
+                gpio_set_level(sda,1); // stop
+                break;
+            }
+            gpio_set_level(scl, 0);
+            i2c_slave_delay_us(5);
+            gpio_set_level(scl, 1);
+        }
+    }
+
+    if (!gpio_get_level(sda) || !gpio_get_level(scl)) { // bus in busy state
+        log_e("Bus Invalid State, Can't init sda=%d, scl=%d",gpio_get_level(sda),gpio_get_level(scl));
+        return false; // bus is busy
+    }
+    return true;
+}
+
+static bool i2c_slave_attach_gpio(i2c_slave_struct_t * i2c, int8_t sda, int8_t scl)
+{
+    if (i2c == NULL) {
+        log_e("no control block");
+        return false;
+    }
+    
+    if ((sda < 0)||( scl < 0)) {
+        log_e("bad pins sda=%d, scl=%d",sda,scl);
+        return false;
+    }
+
+    i2c->scl = scl;
+    gpio_set_level(scl, 1);
+    i2c_slave_gpio_mode(scl, GPIO_MODE_INPUT_OUTPUT_OD);
+    gpio_matrix_out(scl, I2C_SCL_IDX(i2c->num), false, false);
+    gpio_matrix_in(scl, I2C_SCL_IDX(i2c->num), false);
+
+    i2c->sda = sda;
+    gpio_set_level(sda, 1);
+    i2c_slave_gpio_mode(sda, GPIO_MODE_INPUT_OUTPUT_OD);
+    gpio_matrix_out(sda, I2C_SDA_IDX(i2c->num), false, false);
+    gpio_matrix_in(sda, I2C_SDA_IDX(i2c->num), false);
+
+    return true;
+}
+
+static bool i2c_slave_detach_gpio(i2c_slave_struct_t * i2c)
+{
+    if (i2c == NULL) {
+        log_e("no control Block");
+        return false;
+    }
+    if (i2c->scl >= 0) {
+        gpio_matrix_out(i2c->scl, 0x100, false, false);
+        gpio_matrix_in(0x30, I2C_SCL_IDX(i2c->num), false);
+        i2c_slave_gpio_mode(i2c->scl, GPIO_MODE_INPUT);
+        i2c->scl = -1; // un attached
+    }
+    if (i2c->sda >= 0) {
+        gpio_matrix_out(i2c->sda, 0x100, false, false);
+        gpio_matrix_in(0x30, I2C_SDA_IDX(i2c->num), false);
+        i2c_slave_gpio_mode(i2c->sda, GPIO_MODE_INPUT);
+        i2c->sda = -1; // un attached
+    }
+    return true;
+}
+
+static bool i2c_slave_send_event(i2c_slave_struct_t * i2c, i2c_slave_queue_event_t* event)
+{
+    bool pxHigherPriorityTaskWoken = false;
+    if(i2c->event_queue) {
+        if(xQueueSendFromISR(i2c->event_queue, event, (BaseType_t * const)&pxHigherPriorityTaskWoken) != pdTRUE){
+            //log_e("event_queue_full");
+        }
+    }
+    return pxHigherPriorityTaskWoken;
+}
+
+static bool i2c_slave_handle_tx_fifo_empty(i2c_slave_struct_t * i2c)
+{
+    bool pxHigherPriorityTaskWoken = false;
+    uint32_t d = 0, moveCnt = i2c_ll_get_txfifo_len(i2c->dev);
+    while (moveCnt > 0) { // read tx queue until Fifo is full or queue is empty
+        if(xQueueReceiveFromISR(i2c->tx_queue, &d, (BaseType_t * const)&pxHigherPriorityTaskWoken) == pdTRUE){
+            i2c_ll_write_txfifo(i2c->dev, (uint8_t*)&d, 1);
+            moveCnt--;
+        } else {
+            i2c_ll_slave_disable_tx_it(i2c->dev);
+            break;
+        }
+    }
+    return pxHigherPriorityTaskWoken;
+}
+
+static bool i2c_slave_handle_rx_fifo_full(i2c_slave_struct_t * i2c, uint32_t len)
+{
+#if I2C_SLAVE_USE_RX_QUEUE
+    uint32_t d = 0;
+#else
+    uint8_t data[SOC_I2C_FIFO_LEN];
+#endif
+    bool pxHigherPriorityTaskWoken = false;
+#if I2C_SLAVE_USE_RX_QUEUE
+    while (len > 0) {
+        i2c_ll_read_rxfifo(i2c->dev, (uint8_t*)&d, 1);
+        if(xQueueSendFromISR(i2c->rx_queue, &d, (BaseType_t * const)&pxHigherPriorityTaskWoken) != pdTRUE){
+            log_e("rx_queue_full");
+        } else {
+            i2c->rx_data_count++;
+        }
+        if (--len == 0) {
+            len = i2c_ll_get_rxfifo_cnt(i2c->dev);
+        }
+#else
+    if(len){
+        i2c_ll_read_rxfifo(i2c->dev, data, len);
+        if(xRingbufferSendFromISR(i2c->rx_ring_buf, (void*) data, len, (BaseType_t * const)&pxHigherPriorityTaskWoken) != pdTRUE){
+            log_e("rx_ring_buf_full");
+        } else {
+            i2c->rx_data_count += len;
+        }
+#endif
+    }
+    return pxHigherPriorityTaskWoken;
+}
+
+static void i2c_slave_isr_handler(void* arg)
+{
+    bool pxHigherPriorityTaskWoken = false;
+    i2c_slave_struct_t * i2c = (i2c_slave_struct_t *) arg; // recover data
+
+    uint32_t activeInt = i2c_ll_get_intsts_mask(i2c->dev);
+    i2c_ll_clr_intsts_mask(i2c->dev, activeInt);
+    uint8_t rx_fifo_len = i2c_ll_get_rxfifo_cnt(i2c->dev);
+    uint8_t tx_fifo_len = SOC_I2C_FIFO_LEN - i2c_ll_get_txfifo_len(i2c->dev);
+    bool slave_rw = i2c_ll_slave_rw(i2c->dev);
+
+    if(activeInt & I2C_RXFIFO_WM_INT_ENA){ // RX FiFo Full
+        pxHigherPriorityTaskWoken |= i2c_slave_handle_rx_fifo_full(i2c, rx_fifo_len);
+        i2c_ll_slave_enable_rx_it(i2c->dev);//is this necessary?
+    }
+
+    if(activeInt & I2C_TRANS_COMPLETE_INT_ENA){ // STOP
+        if(rx_fifo_len){ //READ RX FIFO
+            pxHigherPriorityTaskWoken |= i2c_slave_handle_rx_fifo_full(i2c, rx_fifo_len);
+        }
+        if(i2c->rx_data_count){ //WRITE or RepeatedStart
+            //SEND RX Event
+            i2c_slave_queue_event_t event;
+            event.event = I2C_SLAVE_EVT_RX;
+            event.stop = !slave_rw;
+            event.param = i2c->rx_data_count;
+            pxHigherPriorityTaskWoken |= i2c_slave_send_event(i2c, &event);
+            //Zero RX count
+            i2c->rx_data_count = 0;
+        }
+        if(slave_rw){ // READ
+#if CONFIG_IDF_TARGET_ESP32
+            //SEND TX Event
+            i2c_slave_queue_event_t event;
+            event.event = I2C_SLAVE_EVT_TX;
+            pxHigherPriorityTaskWoken |= i2c_slave_send_event(i2c, &event);
+#else
+            //reset TX data
+            i2c_ll_txfifo_rst(i2c->dev);
+            uint8_t d;
+            while (xQueueReceiveFromISR(i2c->tx_queue, &d, (BaseType_t * const)&pxHigherPriorityTaskWoken) == pdTRUE) ;//flush partial write
+#endif
+        }
+    }
+
+#ifndef CONFIG_IDF_TARGET_ESP32
+    if(activeInt & I2C_SLAVE_STRETCH_INT_ENA){ // STRETCH
+        i2c_stretch_cause_t cause = i2c_ll_stretch_cause(i2c->dev);
+        if(cause == I2C_STRETCH_CAUSE_MASTER_READ){
+            //on C3 RX data dissapears with repeated start, so we need to get it here
+            if(rx_fifo_len){
+                pxHigherPriorityTaskWoken |= i2c_slave_handle_rx_fifo_full(i2c, rx_fifo_len);
+            }
+            //SEND TX Event
+            i2c_slave_queue_event_t event;
+            event.event = I2C_SLAVE_EVT_TX;
+            pxHigherPriorityTaskWoken |= i2c_slave_send_event(i2c, &event);
+            //will clear after execution
+        } else if(cause == I2C_STRETCH_CAUSE_TX_FIFO_EMPTY){
+            pxHigherPriorityTaskWoken |= i2c_slave_handle_tx_fifo_empty(i2c);
+            i2c_ll_stretch_clr(i2c->dev);
+        } else if(cause == I2C_STRETCH_CAUSE_RX_FIFO_FULL){
+            pxHigherPriorityTaskWoken |= i2c_slave_handle_rx_fifo_full(i2c, rx_fifo_len);
+            i2c_ll_stretch_clr(i2c->dev);
+        }
+    }
+#endif
+
+    if(activeInt & I2C_TXFIFO_WM_INT_ENA){ // TX FiFo Empty
+        pxHigherPriorityTaskWoken |= i2c_slave_handle_tx_fifo_empty(i2c);
+    }
+
+    if(pxHigherPriorityTaskWoken){
+        portYIELD_FROM_ISR();
+    }
+}
+
+static size_t i2c_slave_read_rx(i2c_slave_struct_t * i2c, uint8_t * data, size_t len){
+    if(!len){
+        return 0;
+    }
+#if I2C_SLAVE_USE_RX_QUEUE
+    uint8_t d = 0;
+    BaseType_t res = pdTRUE;
+    for(size_t i=0; i<len; i++) {
+        if(data){
+            res = xQueueReceive(i2c->rx_queue, &data[i], 0);
+        } else {
+            res = xQueueReceive(i2c->rx_queue, &d, 0);
+        }
+        if (res != pdTRUE) {
+            log_e("Read Queue(%u) Failed", i);
+            len = i;
+            break;
+        }
+    }
+    return (data)?len:0;
+#else
+    size_t  dlen = 0, 
+            to_read = len, 
+            so_far = 0, 
+            available = 0;
+    uint8_t * rx_data = NULL;
+
+    vRingbufferGetInfo(i2c->rx_ring_buf, NULL, NULL, NULL, NULL, &available);
+    if(available < to_read){
+        log_e("Less available than requested. %u < %u", available, len);
+        to_read = available;
+    }
+
+    while(to_read){
+        dlen = 0;
+        rx_data = (uint8_t *)xRingbufferReceiveUpTo(i2c->rx_ring_buf, &dlen, 0, to_read);
+        if(!rx_data){
+            log_e("Receive %u Failed", to_read);
+            return so_far;
+        }
+        if(data){
+            memcpy(data+so_far, rx_data, dlen);
+        }
+        vRingbufferReturnItem(i2c->rx_ring_buf, rx_data);
+        so_far+=dlen;
+        to_read-=dlen;
+    }
+    return (data)?so_far:0;
+#endif
+}
+
+static void i2c_slave_task(void *pv_args)
+{
+    i2c_slave_struct_t * i2c = (i2c_slave_struct_t *)pv_args;
+    i2c_slave_queue_event_t event;
+    size_t len = 0;
+    bool stop = false;
+    uint8_t * data = NULL;
+    for(;;){
+        if(xQueueReceive(i2c->event_queue, &event, portMAX_DELAY) == pdTRUE){
+            // Write
+            if(event.event == I2C_SLAVE_EVT_RX){
+                len = event.param;
+                stop = event.stop;
+                data = (len > 0)?(uint8_t*)malloc(len):NULL;
+
+                if(len && data == NULL){
+                    log_e("Malloc (%u) Failed", len);
+                }
+                len = i2c_slave_read_rx(i2c, data, len);
+                if(i2c->receive_callback){
+                    i2c->receive_callback(i2c->num, data, len, stop, i2c->arg);
+                }
+                free(data);
+
+            // Read
+            } else if(event.event == I2C_SLAVE_EVT_TX){
+                if(i2c->request_callback){
+                    i2c->request_callback(i2c->num, i2c->arg);
+                }
+                i2c_ll_stretch_clr(i2c->dev);
+            }
+        }
+    }
+    vTaskDelete(NULL);
+}

cores/esp32/esp32-hal-i2c-slave.h

+// Copyright 2015-2021 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "stdint.h"
+#include "stddef.h"
+#include "esp_err.h"
+
+typedef void (*i2c_slave_request_cb_t) (uint8_t num, void * arg);
+typedef void (*i2c_slave_receive_cb_t) (uint8_t num, uint8_t * data, size_t len, bool stop, void * arg);
+esp_err_t i2cSlaveAttachCallbacks(uint8_t num, i2c_slave_request_cb_t request_callback, i2c_slave_receive_cb_t receive_callback, void * arg);
+
+esp_err_t i2cSlaveInit(uint8_t num, int sda, int scl, uint16_t slaveID, uint32_t frequency, size_t rx_len, size_t tx_len);
+esp_err_t i2cSlaveDeinit(uint8_t num);
+size_t i2cSlaveWrite(uint8_t num, const uint8_t *buf, uint32_t len, uint32_t timeout_ms);
+
+#ifdef __cplusplus
+}
+#endif

libraries/Wire/examples/WireMaster/WireMaster.ino

+#include "Wire.h"
+
+#define I2C_DEV_ADDR 0x55
+
+uint32_t i = 0;
+
+void setup() {
+  Serial.begin(115200);
+  Serial.setDebugOutput(true);
+  Wire.begin();
+}
+
+void loop() {
+  delay(5000);
+
+  //Write message to the slave
+  Wire.beginTransmission(I2C_DEV_ADDR);
+  Wire.printf("Hello World! %u", i++);
+  uint8_t error = Wire.endTransmission(true);
+  Serial.printf("endTransmission: %u\n", error);
+  
+  //Read 16 bytes from the slave
+  error = Wire.requestFrom(I2C_DEV_ADDR, 16);
+  Serial.printf("requestFrom: %u\n", error);
+  if(error){
+    uint8_t temp[error];
+    Wire.readBytes(temp, error);
+    log_print_buf(temp, error);
+  }
+}

libraries/Wire/examples/WireScan/WireScan.ino

+#include "Wire.h"
+
+void setup() {
+  Serial.begin(115200);
+  Wire.begin();
+}
+
+void loop() {
+  byte error, address;
+  int nDevices = 0;
+
+  delay(5000);
+
+  Serial.println("Scanning for I2C devices ...");
+  for(address = 0x01; address < 0x7f; address++){
+    Wire.beginTransmission(address);
+    error = Wire.endTransmission();
+    if (error == 0){
+      Serial.printf("I2C device found at address 0x%02X\n", address);
+      nDevices++;
+    } else if(error != 2){
+      Serial.printf("Error %d at address 0x%02X\n", error, address);
+    }
+  }
+  if (nDevices == 0){
+    Serial.println("No I2C devices found");
+  }
+}

libraries/Wire/examples/WireSlave/WireSlave.ino

+#include "Wire.h"
+
+#define I2C_DEV_ADDR 0x55
+
+uint32_t i = 0;
+
+void onRequest(){
+  Wire.print(i++);
+  Wire.print(" Packets.");
+  Serial.println("onRequest");
+}
+
+void onReceive(int len){
+  Serial.printf("onReceive[%d]: ", len);
+  while(Wire.available()){
+    Serial.write(Wire.read());
+  }
+  Serial.println();
+}
+
+void setup() {
+  Serial.begin(115200);
+  Serial.setDebugOutput(true);
+  Wire.onReceive(onReceive);
+  Wire.onRequest(onRequest);
+  Wire.begin((uint8_t)I2C_DEV_ADDR);
+
+#if CONFIG_IDF_TARGET_ESP32
+  char message[64];
+  snprintf(message, 64, "%u Packets.", i++);
+  Wire.slaveWrite((uint8_t *)message, strlen(message));
+#endif
+}
+
+void loop() {
+
+}

libraries/Wire/src/Wire.cpp

@@ -30,6 +30,7 @@ extern "C" {
 }
 
 #include "esp32-hal-i2c.h"
+#include "esp32-hal-i2c-slave.h"
 #include "Wire.h"
 #include "Arduino.h"
 
@@ -47,6 +48,9 @@ TwoWire::TwoWire(uint8_t bus_num)
     ,nonStopTask(NULL)
     ,lock(NULL)
 #endif
+    ,is_slave(false)
+    ,user_onRequest(NULL)
+    ,user_onReceive(NULL)
 {}
 
 TwoWire::~TwoWire()
@@ -59,6 +63,47 @@ TwoWire::~TwoWire()
 #endif
 }
 
+bool TwoWire::initPins(int sdaPin, int sclPin)
+{
+    if(sdaPin < 0) { // default param passed
+        if(num == 0) {
+            if(sda==-1) {
+                sdaPin = SDA;    //use Default Pin
+            } else {
+                sdaPin = sda;    // reuse prior pin
+            }
+        } else {
+            if(sda==-1) {
+                log_e("no Default SDA Pin for Second Peripheral");
+                return false; //no Default pin for Second Peripheral
+            } else {
+                sdaPin = sda;    // reuse prior pin
+            }
+        }
+    }
+
+    if(sclPin < 0) { // default param passed
+        if(num == 0) {
+            if(scl == -1) {
+                sclPin = SCL;    // use Default pin
+            } else {
+                sclPin = scl;    // reuse prior pin
+            }
+        } else {
+            if(scl == -1) {
+                log_e("no Default SCL Pin for Second Peripheral");
+                return false; //no Default pin for Second Peripheral
+            } else {
+                sclPin = scl;    // reuse prior pin
+            }
+        }
+    }
+
+    sda = sdaPin;
+    scl = sclPin;
+    return true;
+}
+
 bool TwoWire::setPins(int sdaPin, int sclPin)
 {
 #if !CONFIG_DISABLE_HAL_LOCKS
@@ -76,8 +121,7 @@ bool TwoWire::setPins(int sdaPin, int sclPin)
     }
 #endif
     if(!i2cIsInit(num)){
-        sda = sdaPin;
-        scl = sclPin;
+        initPins(sdaPin, sclPin);
     } else {
         log_e("bus already initialized. change pins only when not.");
     }
@@ -88,10 +132,10 @@ bool TwoWire::setPins(int sdaPin, int sclPin)
     return !i2cIsInit(num);
 }
 
-bool TwoWire::begin(int sdaPin, int sclPin, uint32_t frequency)
+// Slave Begin
+bool TwoWire::begin(uint8_t addr, int sdaPin, int sclPin, uint32_t frequency)
 {
     bool started = false;
-    esp_err_t err = ESP_OK;
 #if !CONFIG_DISABLE_HAL_LOCKS
     if(lock == NULL){
         lock = xSemaphoreCreateMutex();
@@ -106,46 +150,64 @@ bool TwoWire::begin(int sdaPin, int sclPin, uint32_t frequency)
         return false;
     }
 #endif
-    if(i2cIsInit(num)){
+    if(is_slave){
+        log_w("Bus already started in Slave Mode.");
         started = true;
         goto end;
     }
-    if(sdaPin < 0) { // default param passed
-        if(num == 0) {
-            if(sda==-1) {
-                sdaPin = SDA;    //use Default Pin
-            } else {
-                sdaPin = sda;    // reuse prior pin
-            }
-        } else {
-            if(sda==-1) {
-                log_e("no Default SDA Pin for Second Peripheral");
-                goto end; //no Default pin for Second Peripheral
-            } else {
-                sdaPin = sda;    // reuse prior pin
+    if(i2cIsInit(num)){
+        log_e("Bus already started in Master Mode.");
+        goto end;
     }
+    if(!initPins(sdaPin, sclPin)){
+        goto end;
     }
+    i2cSlaveAttachCallbacks(num, onRequestService, onReceiveService, this);
+    if(i2cSlaveInit(num, sda, scl, addr, frequency, I2C_BUFFER_LENGTH, I2C_BUFFER_LENGTH) != ESP_OK){
+        log_e("Slave Init ERROR");
+        goto end;
     }
+    is_slave = true;
+    started = true;
+end:
+#if !CONFIG_DISABLE_HAL_LOCKS
+    //release lock
+    xSemaphoreGive(lock);
+#endif
+    return started;
+}
 
-    if(sclPin < 0) { // default param passed
-        if(num == 0) {
-            if(scl == -1) {
-                sclPin = SCL;    // use Default pin
-            } else {
-                sclPin = scl;    // reuse prior pin
+// Master Begin
+bool TwoWire::begin(int sdaPin, int sclPin, uint32_t frequency)
+{
+    bool started = false;
+    esp_err_t err = ESP_OK;
+#if !CONFIG_DISABLE_HAL_LOCKS
+    if(lock == NULL){
+        lock = xSemaphoreCreateMutex();
+        if(lock == NULL){
+            log_e("xSemaphoreCreateMutex failed");
+            return false;
         }
-        } else {
-            if(scl == -1) {
-                log_e("no Default SCL Pin for Second Peripheral");
-                goto end; //no Default pin for Second Peripheral
-            } else {
-                sclPin = scl;    // reuse prior pin
     }
+    //acquire lock
+    if(xSemaphoreTake(lock, portMAX_DELAY) != pdTRUE){
+        log_e("could not acquire lock");
+        return false;
     }
+#endif
+    if(is_slave){
+        log_e("Bus already started in Slave Mode.");
+        goto end;
+    }
+    if(i2cIsInit(num)){
+        log_w("Bus already started in Master Mode.");
+        started = true;
+        goto end;
+    }
+    if(!initPins(sdaPin, sclPin)){
+        goto end;
     }
-
-    sda = sdaPin;
-    scl = sclPin;
     err = i2cInit(num, sda, scl, frequency);
     started = (err == ESP_OK);
 
@@ -169,7 +231,12 @@ bool TwoWire::end()
             return false;
         }
 #endif
-        if(i2cIsInit(num)){
+        if(is_slave){
+            err = i2cSlaveDeinit(num);
+            if(err == ESP_OK){
+                is_slave = false;
+            }
+        } else if(i2cIsInit(num)){
             err = i2cDeinit(num);
         }
 #if !CONFIG_DISABLE_HAL_LOCKS
@@ -189,7 +256,11 @@ uint32_t TwoWire::getClock()
         log_e("could not acquire lock");
     } else {
 #endif
+        if(is_slave){
+            log_e("Bus is in Slave Mode");
+        } else {
             i2cGetClock(num, &frequency);
+        }
 #if !CONFIG_DISABLE_HAL_LOCKS
         //release lock
         xSemaphoreGive(lock);
@@ -208,7 +279,12 @@ bool TwoWire::setClock(uint32_t frequency)
         return false;
     }
 #endif
+    if(is_slave){
+        log_e("Bus is in Slave Mode");
+        err = ESP_FAIL;
+    } else {
         err = i2cSetClock(num, frequency);
+    }
 #if !CONFIG_DISABLE_HAL_LOCKS
     //release lock
     xSemaphoreGive(lock);
@@ -228,6 +304,10 @@ uint16_t TwoWire::getTimeOut()
 
 void TwoWire::beginTransmission(uint16_t address)
 {
+    if(is_slave){
+        log_e("Bus is in Slave Mode");
+        return;
+    }
 #if !CONFIG_DISABLE_HAL_LOCKS
     if(nonStop && nonStopTask == xTaskGetCurrentTaskHandle()){
         log_e("Unfinished Repeated Start transaction! Expected requestFrom, not beginTransmission! Clearing...");
@@ -247,6 +327,10 @@ void TwoWire::beginTransmission(uint16_t address)
 
 uint8_t TwoWire::endTransmission(bool sendStop)
 {
+    if(is_slave){
+        log_e("Bus is in Slave Mode");
+        return 4;
+    }
     esp_err_t err = ESP_OK;
     if(sendStop){
         err = i2cWrite(num, txAddress, txBuffer, txLength, _timeOutMillis);
@@ -272,6 +356,10 @@ uint8_t TwoWire::endTransmission(bool sendStop)
 
 uint8_t TwoWire::requestFrom(uint16_t address, uint8_t size, bool sendStop)
 {
+    if(is_slave){
+        log_e("Bus is in Slave Mode");
+        return 0;
+    }
     esp_err_t err = ESP_OK;
     if(nonStop
 #if !CONFIG_DISABLE_HAL_LOCKS
@@ -402,5 +490,49 @@ uint8_t TwoWire::endTransmission(void)
     return endTransmission(true);
 }
 
+size_t TwoWire::slaveWrite(const uint8_t * buffer, size_t len)
+{
+    return i2cSlaveWrite(num, buffer, len, _timeOutMillis);
+}
+
+void TwoWire::onReceiveService(uint8_t num, uint8_t* inBytes, size_t numBytes, bool stop, void * arg)
+{
+    TwoWire * wire = (TwoWire*)arg;
+    if(!wire->user_onReceive){
+        return;
+    }
+    for(uint8_t i = 0; i < numBytes; ++i){
+        wire->rxBuffer[i] = inBytes[i];    
+    }
+    wire->rxIndex = 0;
+    wire->rxLength = numBytes;
+    wire->user_onReceive(numBytes);
+}
+
+void TwoWire::onRequestService(uint8_t num, void * arg)
+{
+    TwoWire * wire = (TwoWire*)arg;
+    if(!wire->user_onRequest){
+        return;
+    }
+    wire->txLength = 0;
+    wire->user_onRequest();
+    if(wire->txLength){
+        wire->slaveWrite((uint8_t*)wire->txBuffer, wire->txLength);
+    }
+}
+
+void TwoWire::onReceive( void (*function)(int) )
+{
+  user_onReceive = function;
+}
+
+// sets function called on slave read
+void TwoWire::onRequest( void (*function)(void) )
+{
+  user_onRequest = function;
+}
+
+
 TwoWire Wire = TwoWire(0);
 TwoWire Wire1 = TwoWire(1);

libraries/Wire/src/Wire.h

@@ -61,6 +61,13 @@ protected:
     TaskHandle_t nonStopTask;
     SemaphoreHandle_t lock;
 #endif
+private:
+    bool is_slave;
+    void (*user_onRequest)(void);
+    void (*user_onReceive)(int);
+    static void onRequestService(uint8_t, void *);
+    static void onReceiveService(uint8_t, uint8_t*, size_t, bool, void *);
+    bool initPins(int sdaPin, int sclPin);
 
 public:
     TwoWire(uint8_t bus_num);
@@ -70,6 +77,7 @@ public:
     bool setPins(int sda, int scl);
     
     bool begin(int sda=-1, int scl=-1, uint32_t frequency=0); // returns true, if successful init of i2c bus
+    bool begin(uint8_t slaveAddr, int sda=-1, int scl=-1, uint32_t frequency=0);
     bool end();
 
     void setTimeOut(uint16_t timeOutMillis); // default timeout of i2c transactions is 50ms
@@ -123,6 +131,7 @@ public:
 
     void onReceive( void (*)(int) );
     void onRequest( void (*)(void) );
+    size_t slaveWrite(const uint8_t *, size_t);
 };
 
 extern TwoWire Wire;