add Chapter13

Chapter13/uart_c_hal_wrapper/hal/uart/src/uart_stm32.cpp

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+#include <uart_stm32.hpp>
+
+template <typename HalUart>
+hal::uart_stm32<HalUart>::uart_stm32(USART_TypeDef *inst)
+    : instance_(inst)
+{
+}
+
+template <typename HalUart>
+void hal::uart_stm32<HalUart>::init(std::uint32_t baudrate)
+{
+    huart_.Instance = instance_;
+    huart_.Init.BaudRate = baudrate;
+    huart_.Init.WordLength = UART_WORDLENGTH_8B;
+    huart_.Init.StopBits = UART_STOPBITS_1;
+    huart_.Init.Parity = UART_PARITY_NONE;
+    huart_.Init.Mode = UART_MODE_TX_RX;
+    huart_.Init.HwFlowCtl = UART_HWCONTROL_NONE;
+    huart_.Init.OverSampling = UART_OVERSAMPLING_16;
+    huart_.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
+    huart_.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
+    // TODO: add GPIO initialization for real hardware
+    huart_.MspInitCallback = nullptr;
+    HalUart::init(&huart_);
+}
+
+template <typename HalUart>
+void hal::uart_stm32<HalUart>::write(std::span<const char> data) 
+{
+    // we must cast away costness due to ST HAL's API
+    char * data_ptr = const_cast<char *>(data.data());
+    HalUart::transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), data.size(),
+                      HAL_MAX_DELAY);
+}