init

01-HelloOs/os.c

@@ -0,0 +1,22 @@
+#include <stdint.h>
+
+// ref: https://www.activexperts.com/serial-port-component/tutorials/uart/
+#define UART        0x10000000
+#define UART_THR    (uint8_t*)(UART+0x00) // THR:transmitter holding register
+#define UART_LSR    (uint8_t*)(UART+0x05) // LSR:line status register
+#define UART_LSR_EMPTY_MASK 0x40          // LSR Bit 6: Transmitter empty; both the THR and LSR are empty
+
+int lib_putc(char ch) {
+	while ((*UART_LSR & UART_LSR_EMPTY_MASK) == 0);
+	return *UART_THR = ch;
+}
+
+void lib_puts(char *s) {
+	while (*s) lib_putc(*s++);
+}
+
+int os_main(void)
+{
+	lib_puts("Hello OS!\n");
+	return 0;
+}