123 lines
3.8 KiB
C
Executable File
123 lines
3.8 KiB
C
Executable File
#include "screen.h"
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#include "ports.h"
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/* Declaration of private functions */
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int get_cursor_offset();
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void set_cursor_offset(int offset);
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int print_char(char c, int col, int row, char attr);
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int get_offset(int col, int row);
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int get_offset_row(int offset);
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int get_offset_col(int offset);
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/**********************************************************
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* Public Kernel API functions *
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**********************************************************/
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/**
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* Print a message on the specified location
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* If col, row, are negative, we will use the current offset
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*/
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void kprint_at(char *message, int col, int row) {
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/* Set cursor if col/row are negative */
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int offset;
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if (col >= 0 && row >= 0)
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offset = get_offset(col, row);
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else {
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offset = get_cursor_offset();
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row = get_offset_row(offset);
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col = get_offset_col(offset);
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}
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/* Loop through message and print it */
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int i = 0;
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while (message[i] != 0) {
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offset = print_char(message[i++], col, row, WHITE_ON_BLACK);
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/* Compute row/col for next iteration */
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row = get_offset_row(offset);
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col = get_offset_col(offset);
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}
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}
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void kprint(char *message) {
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kprint_at(message, -1, -1);
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}
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/**********************************************************
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* Private kernel functions *
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**********************************************************/
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/**
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* Innermost print function for our kernel, directly accesses the video memory
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*
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* If 'col' and 'row' are negative, we will print at current cursor location
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* If 'attr' is zero it will use 'white on black' as default
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* Returns the offset of the next character
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* Sets the video cursor to the returned offset
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*/
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int print_char(char c, int col, int row, char attr) {
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unsigned char *vidmem = (unsigned char*) VIDEO_ADDRESS;
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if (!attr) attr = WHITE_ON_BLACK;
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/* Error control: print a red 'E' if the coords aren't right */
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if (col >= MAX_COLS || row >= MAX_ROWS) {
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vidmem[2*(MAX_COLS)*(MAX_ROWS)-2] = 'E';
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vidmem[2*(MAX_COLS)*(MAX_ROWS)-1] = RED_ON_WHITE;
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return get_offset(col, row);
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}
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int offset;
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if (col >= 0 && row >= 0) offset = get_offset(col, row);
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else offset = get_cursor_offset();
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if (c == '\n') {
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row = get_offset_row(offset);
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offset = get_offset(0, row+1);
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} else {
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vidmem[offset] = c;
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vidmem[offset+1] = attr;
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offset += 2;
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}
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set_cursor_offset(offset);
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return offset;
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}
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int get_cursor_offset() {
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/* Use the VGA ports to get the current cursor position
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* 1. Ask for high byte of the cursor offset (data 14)
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* 2. Ask for low byte (data 15)
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*/
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port_byte_out(REG_SCREEN_CTRL, 14);
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int offset = port_byte_in(REG_SCREEN_DATA) << 8; /* High byte: << 8 */
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port_byte_out(REG_SCREEN_CTRL, 15);
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offset += port_byte_in(REG_SCREEN_DATA);
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return offset * 2; /* Position * size of character cell */
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}
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void set_cursor_offset(int offset) {
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/* Similar to get_cursor_offset, but instead of reading we write data */
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offset /= 2;
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port_byte_out(REG_SCREEN_CTRL, 14);
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port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset >> 8));
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port_byte_out(REG_SCREEN_CTRL, 15);
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port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset & 0xff));
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}
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void clear_screen() {
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int screen_size = MAX_COLS * MAX_ROWS;
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int i;
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char *screen = (char *) VIDEO_ADDRESS;
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for (i = 0; i < screen_size; i++) {
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screen[i*2] = ' ';
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screen[i*2+1] = WHITE_ON_BLACK;
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}
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set_cursor_offset(get_offset(0, 0));
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}
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int get_offset(int col, int row) { return 2 * (row * MAX_COLS + col); }
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int get_offset_row(int offset) { return offset / (2 * MAX_COLS); }
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int get_offset_col(int offset) { return (offset - (get_offset_row(offset)*2*MAX_COLS))/2; }
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