1 files changed, 103 insertions, 0 deletions
diff --git a/src/utils/uart.c b/src/utils/uart.c
new file mode 100644
index 0000000..4dd1c2b
--- /dev/null
+++ b/src/utils/uart.c
@@ -0,0 +1,103 @@
+#include <stddef.h>
+#include <stdint.h>
+#include "uart.h"
+#include "global.h"
+
+// Loop <delay> times in a way that the compiler won't optimize away
+static inline void delay(int32_t count)
+{
+  asm volatile("__delay_%=: subs %[count], %[count], #1; bne __delay_%=\n"
+	       : "=r"(count): [count]"0"(count) : "cc");
+}
+
+void uart_init()
+{
+  // Disable PL011_UART.
+  wr32(PL011_UART_CR, 0);
+  
+  // Setup the GPIO pin 14 && 15.
+
+  // Disable pull up/down for all GPIO pins & delay for 150 cycles.
+  wr32(GPPUD, 0);
+  delay(150);
+
+  // Disable pull up/down for pin 14,15 & delay for 150 cycles.
+  wr32(GPPUDCLK0, (1 << 14) | (1 << 15));
+  delay(150);
+
+  // Write 0 to GPPUDCLK0 to make it take effect.
+  wr32(GPPUDCLK0, 0);
+
+  // Set integer & fractional part of baud rate.
+  // Divider = UART_CLOCK/(16 * Baud)
+  // Fraction part register = (Fractional part * 64) + 0.5
+  // UART_CLOCK = 3000000; Baud = 115200.
+
+  // Divider = 3000000 / (16 * 115200) = 1.627 = ~1.
+  wr32(PL011_UART_IBRD, 1);
+  // Fractional part register = (.627 * 64) + 0.5 = 40.6 = ~40.
+  wr32(PL011_UART_FBRD, 40);
+
+  // Set 8 bit data transmission (1 stop bit, no parity)
+  // and disable FIFO to be able to receive interrupt every received
+  // char, not every 2 chars
+  wr32(PL011_UART_LCRH, (1 << 5) | (1 << 6));
+
+  // set interrupt to come when transmit FIFO becomes ≤ 1/8 full
+  // or receive FIFO becomes ≥ 1/8 full
+  // (not really matters, since we disabled FIFOs)
+  wr32(PL011_UART_IFLS, 0);
+
+  // Enable PL011_UART, receive & transfer part of UART.2
+  wr32(PL011_UART_CR, (1 << 0) | (1 << 8) | (1 << 9));
+
+  // At first, it's probably safer to disable interrupts :)
+  uart_irq_disable();
+
+  // The above disables the entire uart irq;
+  // Also disable single sources within it
+  wr32(PL011_UART_IMSC, 0);
+}
+
+inline static _Bool can_transmit(void)
+{
+  return !(rd32(PL011_UART_FR) & (1 << 5));
+}
+
+inline static _Bool can_receive(void)
+{
+  return !(rd32(PL011_UART_FR) & (1 << 4));
+}
+
+void putchar(char c)
+{
+  while (!can_transmit());
+  
+  wr32(PL011_UART_DR, c);
+}
+
+char getchar(void)
+{
+  while (!can_receive());
+  
+  return rd32(PL011_UART_DR);
+}
+
+_Bool putchar_non_blocking(char c)
+{
+  if (can_transmit())
+    {
+      wr32(PL011_UART_DR, c);
+      return 0;
+    }
+
+  return 1;
+}
+
+int getchar_non_blocking(void)
+{
+  if (can_receive())
+    return rd32(PL011_UART_DR);
+
+  return -1;
+}