add Chapter04 bare example

Chapter04/bare/hal/uart/src/uart_stm32.cpp

@@ -0,0 +1,33 @@
+#include <uart_stm32.hpp>
+
+hal::uart_stm32::uart_stm32(USART_TypeDef *inst, std::uint32_t baud)
+    : instance(inst), baudrate(baud)
+{
+}
+
+void hal::uart_stm32::init()
+{
+    huart.Instance = USART2;
+    huart.Init.BaudRate = 115200;
+    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;
+
+    // huart.MspInitCallback = mspInitCallback;
+
+    if(HAL_UART_Init(&huart) != HAL_OK)
+    {
+        // Error_Handler();
+    }
+}
+
+void hal::uart_stm32::putchar(char c)
+{
+    HAL_UART_Transmit(&huart, reinterpret_cast<uint8_t *>(&c), 1,
+                      HAL_MAX_DELAY);
+}