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Add i2c slave example (#320)
* Add i2c slave example from https://github.com/vmilea/pico_i2c_slave To test you need to wire pin GP4 to GP6 (SDA), and pin GP5 to GP7 (SCL)
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‎README.md

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[pa1010d_i2c](i2c/pa1010d_i2c) | Read GPS location data, parse and display data via I2C.
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[pcf8523_i2c](i2c/pcf8523_i2c) | Read time and date values from a real time clock. Set current time and alarms on it.
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[ht16k33_i2c](i2c/ht16k33_i2c) | Drive a 4 digit 14 segment LED with an HT16K33.
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[slave_mem_i2c](i2c/slave_mem_i2c) | i2c slave example where the slave implements a 256 byte memory
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### Interpolator
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‎i2c/CMakeLists.txt

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add_subdirectory(pa1010d_i2c)
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add_subdirectory(pcf8523_i2c)
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add_subdirectory(ht16k33_i2c)
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add_subdirectory(slave_mem_i2c)
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endif ()

‎i2c/slave_mem_i2c/CMakeLists.txt

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add_executable(slave_mem_i2c
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slave_mem_i2c.c
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)
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target_link_libraries(slave_mem_i2c
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pico_i2c_slave
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hardware_i2c
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pico_stdlib
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)
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pico_add_extra_outputs(slave_mem_i2c)
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example_auto_set_url(slave_mem_i2c)

‎i2c/slave_mem_i2c/slave_mem_i2c.c

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/*
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* Copyright (c) 2021 Valentin Milea <[email protected]>
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* Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#include <hardware/i2c.h>
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#include <pico/i2c_slave.h>
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#include <pico/stdlib.h>
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#include <stdio.h>
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#include <string.h>
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static const uint I2C_SLAVE_ADDRESS = 0x17;
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static const uint I2C_BAUDRATE = 100000; // 100 kHz
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// For this example, we run both the master and slave from the same board.
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// You'll need to wire pin GP4 to GP6 (SDA), and pin GP5 to GP7 (SCL).
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static const uint I2C_SLAVE_SDA_PIN = PICO_DEFAULT_I2C_SDA_PIN; // 4
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static const uint I2C_SLAVE_SCL_PIN = PICO_DEFAULT_I2C_SCL_PIN; // 5
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static const uint I2C_MASTER_SDA_PIN = 6;
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static const uint I2C_MASTER_SCL_PIN = 7;
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// The slave implements a 256 byte memory. To write a series of bytes, the master first
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// writes the memory address, followed by the data. The address is automatically incremented
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// for each byte transferred, looping back to 0 upon reaching the end. Reading is done
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// sequentially from the current memory address.
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static struct
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{
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uint8_t mem[256];
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uint8_t mem_address;
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bool mem_address_written;
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} context;
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// Our handler is called from the I2C ISR, so it must complete quickly. Blocking calls /
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// printing to stdio may interfere with interrupt handling.
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static void i2c_slave_handler(i2c_inst_t *i2c, i2c_slave_event_t event) {
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switch (event) {
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case I2C_SLAVE_RECEIVE: // master has written some data
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if (!context.mem_address_written) {
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// writes always start with the memory address
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context.mem_address = i2c_read_byte_raw(i2c);
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context.mem_address_written = true;
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} else {
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// save into memory
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context.mem[context.mem_address] = i2c_read_byte_raw(i2c);
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context.mem_address++;
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}
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break;
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case I2C_SLAVE_REQUEST: // master is requesting data
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// load from memory
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i2c_write_byte_raw(i2c, context.mem[context.mem_address]);
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context.mem_address++;
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break;
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case I2C_SLAVE_FINISH: // master has signalled Stop / Restart
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context.mem_address_written = false;
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break;
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default:
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break;
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}
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}
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static void setup_slave() {
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gpio_init(I2C_SLAVE_SDA_PIN);
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gpio_set_function(I2C_SLAVE_SDA_PIN, GPIO_FUNC_I2C);
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gpio_pull_up(I2C_SLAVE_SDA_PIN);
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gpio_init(I2C_SLAVE_SCL_PIN);
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gpio_set_function(I2C_SLAVE_SCL_PIN, GPIO_FUNC_I2C);
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gpio_pull_up(I2C_SLAVE_SCL_PIN);
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i2c_init(i2c0, I2C_BAUDRATE);
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// configure I2C0 for slave mode
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i2c_slave_init(i2c0, I2C_SLAVE_ADDRESS, &i2c_slave_handler);
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}
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static void run_master() {
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gpio_init(I2C_MASTER_SDA_PIN);
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gpio_set_function(I2C_MASTER_SDA_PIN, GPIO_FUNC_I2C);
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// pull-ups are already active on slave side, this is just a fail-safe in case the wiring is faulty
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gpio_pull_up(I2C_MASTER_SDA_PIN);
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gpio_init(I2C_MASTER_SCL_PIN);
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gpio_set_function(I2C_MASTER_SCL_PIN, GPIO_FUNC_I2C);
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gpio_pull_up(I2C_MASTER_SCL_PIN);
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i2c_init(i2c1, I2C_BAUDRATE);
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for (uint8_t mem_address = 0;; mem_address = (mem_address + 32) % 256) {
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char msg[32];
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snprintf(msg, sizeof(msg), "Hello, I2C slave! - 0x%02X", mem_address);
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uint8_t msg_len = strlen(msg);
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uint8_t buf[32];
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buf[0] = mem_address;
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memcpy(buf + 1, msg, msg_len);
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// write message at mem_address
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printf("Write at 0x%02X: '%s'\n", mem_address, msg);
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int count = i2c_write_blocking(i2c1, I2C_SLAVE_ADDRESS, buf, 1 + msg_len, false);
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if (count < 0) {
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puts("Couldn't write to slave, please check your wiring!");
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return;
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}
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hard_assert(count == 1 + msg_len);
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// seek to mem_address
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count = i2c_write_blocking(i2c1, I2C_SLAVE_ADDRESS, buf, 1, true);
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hard_assert(count == 1);
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// partial read
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uint8_t split = 5;
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count = i2c_read_blocking(i2c1, I2C_SLAVE_ADDRESS, buf, split, true);
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hard_assert(count == split);
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buf[count] = '\0';
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printf("Read at 0x%02X: '%s'\n", mem_address, buf);
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hard_assert(memcmp(buf, msg, split) == 0);
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// read the remaining bytes, continuing from last address
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count = i2c_read_blocking(i2c1, I2C_SLAVE_ADDRESS, buf, msg_len - split, false);
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hard_assert(count == msg_len - split);
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buf[count] = '\0';
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printf("Read at 0x%02X: '%s'\n", mem_address + split, buf);
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hard_assert(memcmp(buf, msg + split, msg_len - split) == 0);
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puts("");
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sleep_ms(2000);
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}
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}
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int main() {
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stdio_init_all();
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puts("\nI2C slave example");
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setup_slave();
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run_master();
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}

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