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().

1 files changed, 52 insertions, 0 deletions

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);
+}