Working I2C-controlled digits

mcu/CMakeLists.txt

@@ -16,4 +16,4 @@ pico_enable_stdio_usb(qclk 1)
 pico_enable_stdio_uart(qclk 0)
 
 pico_add_extra_outputs(qclk)
-target_link_libraries(qclk pico_stdlib)
+target_link_libraries(qclk pico_stdlib hardware_i2c pico_i2c_slave)

mcu/main.c

@@ -1,27 +1,33 @@
 #include <stdio.h>
 
 #include "hardware/gpio.h"
+#include "hardware/i2c.h"
 #include "pico/stdlib.h"
 #include "pico/binary_info.h"
+#include "pico/i2c_slave.h"
 
 const uint PIN_DIGIT_BASE = 18;
 const uint PIN_SEGMENT_BASE = 2;
 
 const uint N_DIGITS = 4;
 
-uint8_t digit_states[4] = { 0b11001100, 0b11111111, 0b10101010, 0b00101001 };
+const uint I2C_PIN_SDA = 0;
+const uint I2C_PIN_SCL = 1;
+const uint I2C_SLAVE_ADDRESS = 0x17;
+const uint I2C_RATE = 100 * 1000;
 
-void write_digit(uint8_t digit) {
+uint8_t digit_states[4] = { 0 };
+static struct {
+  bool digit_written;
+  uint digit;
+} i2c_context;
+
+static void write_digit(uint8_t digit) {
   const uint mask = (0xffffffff << PIN_SEGMENT_BASE) ^ (0xffffffff << PIN_SEGMENT_BASE + 8);
   gpio_put_masked(mask, (~digit & 0xff) << PIN_SEGMENT_BASE);
   gpio_put_masked(mask, digit << PIN_SEGMENT_BASE);
 }
-
-int main() {
-  bi_decl(bi_program_description("qCLK driver."));
-
-  stdio_init_all();
-
+static void setup_io() {
   for (uint i = PIN_DIGIT_BASE; i < PIN_DIGIT_BASE + N_DIGITS; i++) {
     gpio_init(i);
     gpio_set_dir(i, GPIO_OUT);
@@ -32,14 +38,65 @@ int main() {
     gpio_set_dir(i, GPIO_OUT);
   }
   write_digit(0);
+}
+static void display_loop() {
+  for (uint i = 0; i < N_DIGITS; i++) {
+    uint prev = i == 0 ? N_DIGITS - 1 : i - 1;
 
-  while (1) {
-    for (uint i = 0; i < N_DIGITS; i++) {
-      uint prev = i == 0 ? N_DIGITS - 1 : i - 1;
-      gpio_put(PIN_DIGIT_BASE + prev, 0);
-      write_digit(digit_states[i]);
-      gpio_put(PIN_DIGIT_BASE + i, 1);
-      sleep_ms(1);
-    }
+    gpio_put(PIN_DIGIT_BASE + prev, 0);
+    sleep_us(100);
+
+    write_digit(digit_states[i]);
+    gpio_put(PIN_DIGIT_BASE + i, 1);
+    sleep_ms(1);
   }
 }
+
+static void i2c_slave_handler(i2c_inst_t *i2c, i2c_slave_event_t event) {
+  switch (event) {
+  case I2C_SLAVE_RECEIVE: // master has written some data
+    if (!i2c_context.digit_written) {
+        // writes always start with the memory address
+        uint8_t addr = i2c_read_byte_raw(i2c);
+        i2c_context.digit = addr < N_DIGITS ? addr : -1;
+        i2c_context.digit_written = true;
+    } else if (i2c_context.digit != -1) {
+        // save into memory
+        digit_states[i2c_context.digit] = i2c_read_byte_raw(i2c);
+    }
+    break;
+  case I2C_SLAVE_REQUEST: // master is requesting data
+    // load from memory
+    uint8_t data = i2c_context.digit != -1 ? digit_states[i2c_context.digit] : 0;
+    i2c_write_byte_raw(i2c, data);
+    break;
+  case I2C_SLAVE_FINISH: // master has signalled Stop / Restart
+    i2c_context.digit_written = false;
+    break;
+  default:
+    break;
+  }
+}
+static void setup_i2c() {
+  gpio_init(I2C_PIN_SDA);
+  gpio_set_function(I2C_PIN_SDA, GPIO_FUNC_I2C);
+  gpio_pull_up(I2C_PIN_SDA);
+
+  gpio_init(I2C_PIN_SCL);
+  gpio_set_function(I2C_PIN_SCL, GPIO_FUNC_I2C);
+  gpio_pull_up(I2C_PIN_SCL);
+
+  i2c_init(i2c0, I2C_RATE);
+  // configure I2C0 for slave mode
+  i2c_slave_init(i2c0, I2C_SLAVE_ADDRESS, &i2c_slave_handler);
+}
+
+int main() {
+  bi_decl(bi_program_description("qCLK driver."));
+
+  stdio_init_all();
+  setup_io();
+  setup_i2c();
+
+  while (1) display_loop();
+}