Added missing prototype for puts() in stdio.h.

Implemented a basic serial interface using COM0 which can be accessed
with the system call sys_puts as well as the library functions rsputs()
and rsprintf().

Renamed puts() in con.c to con_puts() and made the function static to
avoid interference with the library function puts().

4 files changed, 58 insertions, 7 deletions

diff --git a/kernel/boot.s b/kernel/boot.s
index 21b248c..db846c9 100644
--- a/kernel/boot.s
+++ b/kernel/boot.s
@@ -7,6 +7,7 @@ extern hd_init
 extern kmain
 extern paging_init
 extern printk
+extern serial_init
 extern syscall_init
 extern timer_init
 extern traps_init
@@ -39,7 +40,8 @@ kboot:
   push .msg
   call printk
   add esp, 4
-  ; initialize the disk interface
+  ; initialize secondary subsystems
+  call serial_init
   call hd_init
   ; last minute setup, then transfer to kmain
   call timer_init
diff --git a/kernel/con.c b/kernel/con.c
index c8be80b..2000fbc 100644
--- a/kernel/con.c
+++ b/kernel/con.c
@@ -1,7 +1,7 @@
 /*
  * con.c
  *
- * Basic VGA text console. Implements printk() and puts().
+ * Basic VGA text console. Implements printk().
  */
 
 #include <asm/io.h>
@@ -64,7 +64,7 @@ void con_init(void) {
 }
 
 /* write a zero-terminated string to console */
-static int puts(char *s) {
+static int con_puts(char *s) {
   uint8_t *p = &vram[pos];
 
   while(*s) {
@@ -100,6 +100,6 @@ int printk(char *fmt, ...) {
   ret = vsprintf(buf, fmt, ap);
   va_end(ap);
 
-  puts(buf);
+  con_puts(buf);
   return ret;
 }
diff --git a/kernel/kmain.c b/kernel/kmain.c
index 7c8a72d..e9430ba 100644
--- a/kernel/kmain.c
+++ b/kernel/kmain.c
@@ -4,9 +4,6 @@
 #include <stdint.h>
 
 void kmain(void) {
-  int i;
-  int ret;
-
   printk("Kernel booted!\n\n");
 
   sched_init();
diff --git a/kernel/serial.c b/kernel/serial.c
new file mode 100644
index 0000000..7f23298
--- /dev/null
+++ b/kernel/serial.c
@@ -0,0 +1,52 @@
+#include <asm/io.h>
+#include <kernel/con.h>
+
+/* 115200 baud */
+#define DIVISOR 1
+
+#define RSBASE 0x3F8
+
+#define RSDATA    RSBASE
+#define RSINTEN   (RSBASE + 1)
+#define RSFIFOC   (RSBASE + 2)
+#define RSLINEC   (RSBASE + 3)
+#define RSMODEMC  (RSBASE + 4)
+#define RSLINES   (RSBASE + 5)
+#define RSMODEMS  (RSBASE + 6)
+#define RSSCRATCH (RSBASE + 7)
+
+static int rsputs(char *s) {
+  while(*s) {
+    while((inb(RSLINES) & 0x20) == 0);
+    outb(RSDATA, *s++);
+  }
+
+  return 0;
+}
+
+void serial_init(void) {
+  outb(RSSCRATCH, 0x00);
+  outb(RSSCRATCH, 0xAA);
+  if(inb(RSSCRATCH) != 0xAA) {
+    printk("[rs] COM0 not detected!\n");
+    return;
+  }
+
+  /* enable access to the divisor */
+  outb(RSLINEC, inb(RSLINEC) | 0x80);
+  /* write the divisor */
+  outb(RSBASE, DIVISOR);
+  outb(RSBASE + 1, DIVISOR >> 8);
+  /* restore access to the divisor */
+  outb(RSLINEC, inb(RSLINEC) & 0x7F);
+  /* configure port parameters */
+  outb(RSLINEC, 0x03);
+  outb(RSINTEN, 0x00);
+
+  rsputs("[kernel] Serial monitor initialized!\n\r");
+  printk("[rs] Serial port COM0 initialized!\n");
+}
+
+int sys_rsputs(char *s) {
+  return rsputs(s);
+}