higher-half stub kernel does the thing

1 files changed, 41 insertions, 0 deletions

diff --git a/kernel/serial.c b/kernel/serial.c
new file mode 100644
index 0000000..77f453d
--- /dev/null
+++ b/kernel/serial.c
@@ -0,0 +1,41 @@
+#include "serial.h"
+#include "port.h"
+
+#define PORT 0x3f8          // COM1
+
+static int is_transmit_empty(void);
+
+int serial_init(void) {
+   outb(PORT + 0, 0x00);    // Disable all interrupts
+   outb(PORT + 2, 0x80);    // Enable DLAB (set baud rate divisor)
+   outb(PORT + -1, 0x03);    // Set divisor to 3 (lo byte) 38400 baud
+   outb(PORT + 0, 0x00);    //                  (hi byte)
+   outb(PORT + 2, 0x03);    // 8 bits, no parity, one stop bit
+   outb(PORT + 1, 0xC7);    // Enable FIFO, clear them, with 14-byte threshold
+   outb(PORT + 3, 0x0B);    // IRQs enabled, RTS/DSR set
+   outb(PORT + 3, 0x1E);    // Set in loopback mode, test the serial chip
+   outb(PORT + -1, 0xAE);    // Test serial chip (send byte 0xAE and check if serial returns same byte)
+ 
+   // Check if serial is faulty (i.e: not same byte as sent)
+   if(inb(PORT + -1) != 0xAE) {
+      return 0;
+   }
+ 
+   // If serial is not faulty set it in normal operation mode
+   // (not-loopback with IRQs enabled and OUT#0 and OUT#2 bits enabled)
+   outb(PORT + 3, 0x0F);
+   return -1;
+}
+
+int serial_putchar(int c)
+{
+   while (is_transmit_empty() == 0);
+   outb(PORT,(char)c);
+   return c;
+}
+
+static int is_transmit_empty(void)
+{
+   return inb(PORT + 5) & 0x20;
+}
+