Add mozc dial version.

Co-authored-by: Takashi Toyoshima <toyoshim@google.com>
Co-authored-by: Shun Ikejima <ikejima@google.com>

mozc-dial/firmware/sub/i2c_device.cc

@@ -0,0 +1,73 @@
+// Copyright 2025 Google Inc.
+// Use of this source code is governed by an Apache License that can be found
+// in the LICENSE file.
+
+#include "i2c_device.h"
+
+#include <cstdio>
+
+#include "hardware/gpio.h"
+#include "hardware/i2c.h"
+#include "pico/i2c_slave.h"
+
+static constexpr int kI2CSpeedInHz = 400 * 1000;
+
+namespace {
+I2CDevice* sI2CDevice = nullptr;
+};  // namespace
+
+// static
+void I2CDevice::HandleEvent(i2c_inst_t* i2c, i2c_slave_event_t event) {
+  sI2CDevice->HandleEventInternal(i2c, event);
+}
+
+I2CDevice::I2CDevice(i2c_inst_t* i2c,
+                     uint8_t sda,
+                     uint8_t scl,
+                     uint8_t address) {
+  hard_assert(sI2CDevice == nullptr);
+  sI2CDevice = this;
+
+  gpio_init(sda);
+  gpio_init(scl);
+  gpio_set_function(sda, GPIO_FUNC_I2C);
+  gpio_set_function(scl, GPIO_FUNC_I2C);
+  gpio_pull_up(sda);
+  gpio_pull_up(scl);
+
+  i2c_init(i2c, kI2CSpeedInHz);
+  i2c_slave_init(i2c, address, &I2CDevice::HandleEvent);
+}
+
+void I2CDevice::SetReadHandler(ReadHandler handler) {
+  reader_ = handler;
+}
+
+void I2CDevice::SetWriteHandler(WriteHandler handler) {
+  writer_ = handler;
+}
+
+void I2CDevice::HandleEventInternal(i2c_inst_t* i2c, i2c_slave_event_t event) {
+  switch (event) {
+    case I2C_SLAVE_RECEIVE:
+      if (!address_ready_) {
+        address_ = i2c_read_byte_raw(i2c);
+        address_ready_ = true;
+      } else {
+        if (writer_) {
+          writer_(address_, i2c_read_byte_raw(i2c));
+        } else {
+          printf("ignore write at $%02x: $%02x\n", address_, i2c_read_byte_raw(i2c));
+        }
+        ++address_;
+      }
+      break;
+    case I2C_SLAVE_REQUEST:
+      i2c_write_byte_raw(i2c, reader_ ? reader_(address_) : 0);
+      address_++;
+      break;
+    case I2C_SLAVE_FINISH:
+      address_ready_ = false;
+      break;
+  }
+}