improved uart character printing and poweroff/restart

src/drivers/uart.c

@@ -0,0 +1,27 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <drivers/uart.h>
+
+void uart_put(size_t base_addr, uint8_t data) {
+	*(volatile uint8_t *)base_addr = data;
+}
+
+int kputchar(int ch) {
+	uart_put(UART_ADDRESS, ch);
+	return ch;
+}
+
+void kprint(const char *str) {
+	while (*str) {
+		kputchar(*str++);
+	}
+}
+
+void knewline(void) {
+	kputchar('\n');
+}
+
+void kputs(const char *str) {
+	kprint(str);
+	knewline();
+}

src/drivers/uart.h

@@ -0,0 +1,9 @@
+#ifndef UART_H
+#define UART_H
+
+#define UART_ADDRESS 0x10000000
+void uart_put(size_t base_addr, uint8_t data);
+int kputchar(int ch);
+void kputs(const char *str);
+void kprint(const char *str);
+#endif

src/kernel/kernel.c

@@ -1,11 +1,9 @@
 #include <stdint.h>
 #include <stddef.h>
+#include <drivers/uart.h>
+#include <syscon/syscon.h>
 
 void kmain() {
-    char *uart = (char *)0x10000000;
-    char *msg = "Hello, OS World!\n";
-    
-    for (int i = 0; msg[i] != '\0'; i++) {
-        *uart = msg[i]; // Write each character to the UART
-    }
+    kprint("Hello, OS World!\n");
+    poweroff();
 }

src/syscon/syscon.c

@@ -0,0 +1,14 @@
+#include <stdint.h>
+#include <stddef.h>
+#include "syscon.h"
+#include "drivers/uart.h"
+
+void poweroff(void) {
+  kputs("Poweroff requested");
+  *(uint32_t *)SYSCON_ADDR = 0x5555;
+}
+
+void reboot(void) {
+  kputs("Reboot requested");
+  *(uint32_t *)SYSCON_ADDR = 0x7777;
+}

src/syscon/syscon.h

@@ -0,0 +1,11 @@
+#ifndef SYSCON_H
+#define SYSCON_H
+
+// "test" syscon-compatible device is at memory-mapped address 0x100000
+// according to our device tree
+#define SYSCON_ADDR 0x100000
+
+void poweroff(void);
+void reboot(void);
+
+#endif