1 files changed, 93 insertions, 0 deletions
diff --git a/02-usart/src/main.c b/02-usart/src/main.c
new file mode 100644
index 0000000..5af52ed
--- /dev/null
+++ b/02-usart/src/main.c
@@ -0,0 +1,93 @@
+
+#include "clock.h"
+#include "delay.h"
+#include "gpio.h"
+#include "spin.h"
+#include "usart.h"
+
+volatile uint32_t delay_amt = 20000000 / 4;
+
+int enable_usart2(uint32_t baud_rate)
+{
+  __IO gpio_port_t* port_a = enable_gpio(GPIO_PORT_A);
+  enable_hsi(&RCC, true);
+
+  // Turn on the clock for the USART2 peripheral
+  set_usart2_clock_src(&RCC, USART_CLK_SRC_HSI16);
+  set_usart2_clock_enabled(&RCC, true);
+
+  // Configure the I/O pins.  Will use PA2 as TX and PA15 as RX so setup for
+  // alternate function
+  set_gpio_pin_mode(port_a, PIN_2, MODE_ALTERNATE);
+  set_gpio_pin_mode(port_a, PIN_15, MODE_ALTERNATE);
+  set_gpio_alternate_function(port_a, PIN_2, AFN_7);
+  set_gpio_alternate_function(port_a, PIN_15, AFN_3);
+
+  // De-assert reset of USART2
+  RCC.apb1rst1_r &= ~BIT(17);
+
+  // Configure the USART
+  // disable USART first to allow setting of other control bits
+  // This also disables parity checking and enables 16 times oversampling
+
+  USART2.c_r1 = 0;
+  USART2.c_r2 = 0;
+  USART2.c_r3 = 0;
+
+  usart_set_divisor(&USART2, 16000000 / baud_rate);
+  usart_set_enabled(&USART2, USART_ENABLE_TX | USART_ENABLE_RX);
+}
+
+int enable_usart1(uint32_t baud_rate)
+{
+  /* Enable the GPIO bus. */
+  __IO gpio_port_t* port_b = enable_gpio(GPIO_PORT_B);
+
+  /* Enable the USART clock. */
+  RCC.apb2en_r |= BIT(14);
+
+  /* == Configure the IO Pins. == */
+
+  /* GPIO D5 (Port B pin 6) is USART1 Tx,
+   * GPIO D6 (Port B pin 7) is USART1 Rx. */
+  set_gpio_pin_mode(port_b, PIN_6, MODE_ALTERNATE);
+  set_gpio_pin_mode(port_b, PIN_7, MODE_ALTERNATE);
+
+  /* Set the GPIO pins to use the USART alternate function. */
+  set_gpio_alternate_function(port_b, PIN_6, AFN_7);
+  set_gpio_alternate_function(port_b, PIN_7, AFN_7);
+
+  RCC.apb2rst_r &= ~BIT(14); /* De-assert reset of USART1 */
+
+  uint32_t baud_rate_div = 80000000 / baud_rate;
+  USART1.c_r1 = 0;
+  USART1.c_r2 = 0;
+  USART1.c_r3 = 0;
+  USART1.br_r = baud_rate_div;
+
+  USART1.c_r1 |= BIT(3) | BIT(2);
+  USART1.c_r1 |= BIT(0);
+
+  /* Enable the transmitter and the receiver. */
+  usart_set_enabled(&USART1, USART_ENABLE_TX);
+  asm volatile(" cpsie i ");
+}
+
+/* Main function. This gets executed from the interrupt vector defined above. */
+int main()
+{
+  /* Enable the GPIO port B. */
+
+  __IO gpio_port_t* port_b = enable_gpio(GPIO_PORT_B);
+  gpio_output_pin_t pin3 = set_gpio_pin_output(port_b, PIN_3);
+  gpio_output_pin_t pin1 = set_gpio_pin_output(port_b, PIN_1);
+
+  /* Enable a higher clock frequency. */
+  set_system_clock_MHz(80);
+
+  enable_usart2(115200);
+
+  pin_on(pin3);
+  usart_transmit_str(&USART2, "Hello, World\n");
+  for(;;);
+}