add Chapter13

Chapter13/uart_c_hal_wrapper/hal/uart/inc/stm32f0xx_hal_uart.hpp

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+#pragma once
+
+#include <stm32f0xx_hal.h>
+#include <stm32f072xb.h>
+
+namespace hal::stm32{
+    struct uart {
+        uart() = delete;
+
+        static inline HAL_StatusTypeDef init(UART_HandleTypeDef *huart) {
+            return HAL_UART_Init(huart);
+        }
+
+        static inline HAL_StatusTypeDef transmit(UART_HandleTypeDef *huart, 
+                                                uint8_t *pData, 
+                                                uint16_t Size, 
+                                                uint32_t Timeout) {
+            return HAL_UART_Transmit(huart, pData, Size, Timeout);
+        }
+    };
+};

Chapter13/uart_c_hal_wrapper/hal/uart/inc/uart.hpp

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+#pragma once
+
+#include <cstdint>
+#include <span>
+
+namespace hal
+{
+class uart
+{
+  public:
+    virtual void init(std::uint32_t baudrate) = 0;
+    virtual void write(std::span<const char> data) = 0;
+};
+}; // namespace hal

Chapter13/uart_c_hal_wrapper/hal/uart/inc/uart_stm32.hpp

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+#pragma once
+
+#include <span>
+#include <cstdint>
+
+#include <uart.hpp>
+
+#include <stm32f0xx_hal_uart.hpp>
+
+namespace hal
+{
+template <typename HalUart>
+class uart_stm32 : public uart
+{
+  public:
+    uart_stm32(USART_TypeDef *inst) : instance_(inst) {}
+
+    void init(std::uint32_t baudrate = c_baudrate_default) override {
+      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_);
+    }
+    void write(std::span<const char> data) override {
+      // 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);
+    }
+
+  private:
+    UART_HandleTypeDef huart_;
+    USART_TypeDef *instance_;
+    std::uint32_t baudrate_;
+    static constexpr std::uint32_t c_baudrate_default = 115200;
+};
+}; // namespace hal