# Serial port configurations

* Implementing some serial port control in preparation to do debugging with bochs

* Changed naming of io to fb_ports to finally[tm] ports

fb.h

@@ -1,6 +0,0 @@
-#ifndef INCLUDE_IO_H
-#define INCLUDE_IO_H
-
-void fb_cursor_control(unsigned short, unsigned char);
-
-#endif /* INCLUDE_IO_H */

fb.s

@@ -1,10 +0,0 @@
-; Helpers for frame buffer which pretty much have to to be 
-; written in asm
-
-global fb_cursor_control
-
-fb_cursor_control:
-	mov al, [esp+8]
-	mov dx, [esp+4]
-	out dx, al
-	ret

framebuffer.c

@@ -29,9 +29,9 @@ void clear_fb(void) {
 
 // Takes the linear indexed position to move the cursos, if there is nothing at that position we should still have something there
 void fb_move_cursor(u16 position) {
-	fb_cursor_control(FB_CMD, FB_HIGH_CMD);
-	fb_cursor_control(FB_DATA, ((position >> 8) & 0x00ff) );
-	fb_cursor_control(FB_CMD, FB_LOW_CMD);
-	fb_cursor_control(FB_DATA, position & 0x00ff);
+	serial_control(FB_CMD, FB_HIGH_CMD);
+	serial_control(FB_DATA, ((position >> 8) & 0x00ff) );
+	serial_control(FB_CMD, FB_LOW_CMD);
+	serial_control(FB_DATA, position & 0x00ff);
 }
 

framebuffer.h

@@ -1,5 +1,6 @@
 #include "types.h"
-#include "fb.h"
+#include "serial.h"
+#include "ports.h"
 
 #define COLUMNS 80
 #define ROWS 25
@@ -38,9 +39,11 @@
 
 extern s32 Frame_Buffer_Cursor;
 
+// Serial wrapper for
 void write_cell_fb(u8, u8, u8);
 
 void clear_fb(void);
 
 void fb_move_cursor(u16);
 
+

ports.h

@@ -0,0 +1,9 @@
+#include "types.h"
+
+#ifndef INCLUDE_IO_H
+#define INCLUDE_IO_H
+
+void serial_control(const u16, const u16);
+
+u8 serial_read_buffer(const u16);
+#endif /* INCLUDE_IO_H */

ports.s

@@ -0,0 +1,45 @@
+; Helpers for frame buffer which pretty much have to to be 
+; written in asm
+
+
+; COM1 Base Port
+%define SERIAL_COM1_BASE 				0x3F8
+
+%define SERIAL_DATA_PORT(base) 			(base)
+%define SERIAL_FIFO_COMMAND_PORT(base) 	(base+2)
+%define SERIAL_LINE_COMMAND_PORT(base) 	(base+3)
+%define SERIAL_MODEM_COMMAND_PORT(base) (base+4)
+%define SERIAL_LINE_STATUS_PORT(base) 	(base+5)
+
+%define SERIAL_DATA_
+global serial_control
+global serial_read_buffer
+
+serial_control:
+	push ebp
+	mov ebp, esp
+	add esp, 0xc 	; ebp + 2 local vars (32-bit kernel)
+
+	mov al, [esp+8]
+	mov dx, [esp+4]
+	out dx, al
+
+	mov esp, ebp
+	pop ebp
+	ret
+
+; Read byte from serial port
+serial_read_buffer:
+	push ebp
+	mov ebp, esp
+	push ebx
+
+	xor eax, eax
+	mov dx, [esp + 4] 	; grab the address of the targeted port
+	in al, dx 			; read byte from the port 
+
+	mov esp, ebp
+	pop ebx
+	pop ebp
+	ret
+

serial.c

@@ -0,0 +1,38 @@
+#include "serial.h"
+
+/*
+ * SERIAL_LINE_COMMAND_PORT configuration
+ * Bit:     | 7 | 6 | 5 4 3 | 2 | 1 0 |
+ * Content: | d | b | prty  | s | dl  |
+ * d = enable/disable DLAB
+ * b = enable/disable break control
+ * prty = # of parity bits to use
+ * s = # no of stop bits [0 is 1] and [1 is 1.5 or 2]
+ * dl = length of data
+ *
+ */
+
+void serial_set_buad_rate(const u16 com_port, const u16 divisor) {
+	// Activate line - ready to send higher 8 bits of data
+	// send the higher 8 bits first
+	// send the lower 8 bits next
+
+	serial_control(SERIAL_LINE_COMMAND_PORT(com_port), 
+			SERIAL_LINE_ENABLE);
+
+	serial_control(SERIAL_DATA_PORT(com_port), 
+			(divisor>>8) & 0x00ff);
+
+	serial_control(SERIAL_DATA_PORT(com_port), 
+			divisor & 0x00ff);
+}
+
+// Payload described above
+void serial_configure_line(const u16 line, const u8 payload) {
+	serial_control(SERIAL_LINE_COMMAND_PORT(line), payload);
+}
+
+u8 serial_fifo_empty(const u16 com_port) {
+	// If the 5th bit is set then we know that the fifo queue is empty
+	return serial_read_buffer(SERIAL_LINE_STATUS_PORT(com_port)) & 0x20;
+}

serial.h

@@ -0,0 +1,26 @@
+#include "types.h"
+#include "ports.h"
+
+// Serial driver interface
+
+#define SERIAL_COM1_BASE 				0x3F8
+
+#define SERIAL_DATA_PORT(base) 			(base)
+#define SERIAL_FIFO_COMMAND_PORT(base) 	(base+2)
+#define SERIAL_LINE_COMMAND_PORT(base) 	(base+3)
+#define SERIAL_MODEM_COMMAND_PORT(base) (base+4)
+#define SERIAL_LINE_STATUS_PORT(base) 	(base+5)
+
+#define SERIAL_LINE_ENABLE 				0x80
+
+// Default configurations for serial ports/lines/buffers etc.
+// Rational can be found here: https://littleosbook.github.io/#configuring-the-buffers
+#define SERIAL_DEFAULT_LINE_CFG 0X03
+#define SERIAL_DEFAULT_BUFFER_CFG 0xc7
+#define SERIAL_DEFAULT_MODEM_CFG 0x03
+
+void serial_set_buad_rate(const u16, const u16);
+
+void serial_configure_line(const u16, const u8); 
+
+u8 serial_fifo_empty(const u16);