lesson 20, preliminar

20-interrupts-timer/drivers/ports.c

@@ -0,0 +1,37 @@
+#include "ports.h"
+
+/**
+ * Read a byte from the specified port
+ */
+u8 port_byte_in (u16 port) {
+    u8 result;
+    /* Inline assembler syntax
+     * !! Notice how the source and destination registers are switched from NASM !!
+     *
+     * '"=a" (result)'; set '=' the C variable '(result)' to the value of register e'a'x
+     * '"d" (port)': map the C variable '(port)' into e'd'x register
+     *
+     * Inputs and outputs are separated by colons
+     */
+    __asm__("in %%dx, %%al" : "=a" (result) : "d" (port));
+    return result;
+}
+
+void port_byte_out (u16 port, u8 data) {
+    /* Notice how here both registers are mapped to C variables and
+     * nothing is returned, thus, no equals '=' in the asm syntax 
+     * However we see a comma since there are two variables in the input area
+     * and none in the 'return' area
+     */
+    __asm__ __volatile__("out %%al, %%dx" : : "a" (data), "d" (port));
+}
+
+u16 port_word_in (u16 port) {
+    u16 result;
+    __asm__("in %%dx, %%ax" : "=a" (result) : "d" (port));
+    return result;
+}
+
+void port_word_out (u16 port, u16 data) {
+    __asm__ __volatile__("out %%ax, %%dx" : : "a" (data), "d" (port));
+}

20-interrupts-timer/drivers/ports.h

@@ -0,0 +1,11 @@
+#ifndef PORTS_H
+#define PORTS_H
+
+#include "../cpu/types.h"
+
+unsigned char port_byte_in (u16 port);
+void port_byte_out (u16 port, u8 data);
+unsigned short port_word_in (u16 port);
+void port_word_out (u16 port, u16 data);
+
+#endif

20-interrupts-timer/drivers/screen.c

@@ -0,0 +1,139 @@
+#include "screen.h"
+#include "ports.h"
+#include "../kernel/util.h"
+
+/* Declaration of private functions */
+int get_cursor_offset();
+void set_cursor_offset(int offset);
+int print_char(char c, int col, int row, char attr);
+int get_offset(int col, int row);
+int get_offset_row(int offset);
+int get_offset_col(int offset);
+
+/**********************************************************
+ * Public Kernel API functions                            *
+ **********************************************************/
+
+/**
+ * Print a message on the specified location
+ * If col, row, are negative, we will use the current offset
+ */
+void kprint_at(char *message, int col, int row) {
+    /* Set cursor if col/row are negative */
+    int offset;
+    if (col >= 0 && row >= 0)
+        offset = get_offset(col, row);
+    else {
+        offset = get_cursor_offset();
+        row = get_offset_row(offset);
+        col = get_offset_col(offset);
+    }
+
+    /* Loop through message and print it */
+    int i = 0;
+    while (message[i] != 0) {
+        offset = print_char(message[i++], col, row, WHITE_ON_BLACK);
+        /* Compute row/col for next iteration */
+        row = get_offset_row(offset);
+        col = get_offset_col(offset);
+    }
+}
+
+void kprint(char *message) {
+    kprint_at(message, -1, -1);
+}
+
+
+/**********************************************************
+ * Private kernel functions                               *
+ **********************************************************/
+
+
+/**
+ * Innermost print function for our kernel, directly accesses the video memory 
+ *
+ * If 'col' and 'row' are negative, we will print at current cursor location
+ * If 'attr' is zero it will use 'white on black' as default
+ * Returns the offset of the next character
+ * Sets the video cursor to the returned offset
+ */
+int print_char(char c, int col, int row, char attr) {
+    unsigned char *vidmem = (unsigned char*) VIDEO_ADDRESS;
+    if (!attr) attr = WHITE_ON_BLACK;
+
+    /* Error control: print a red 'E' if the coords aren't right */
+    if (col >= MAX_COLS || row >= MAX_ROWS) {
+        vidmem[2*(MAX_COLS)*(MAX_ROWS)-2] = 'E';
+        vidmem[2*(MAX_COLS)*(MAX_ROWS)-1] = RED_ON_WHITE;
+        return get_offset(col, row);
+    }
+
+    int offset;
+    if (col >= 0 && row >= 0) offset = get_offset(col, row);
+    else offset = get_cursor_offset();
+
+    if (c == '\n') {
+        row = get_offset_row(offset);
+        offset = get_offset(0, row+1);
+    } else {
+        vidmem[offset] = c;
+        vidmem[offset+1] = attr;
+        offset += 2;
+    }
+
+    /* Check if the offset is over screen size and scroll */
+    if (offset >= MAX_ROWS * MAX_COLS * 2) {
+        int i;
+        for (i = 1; i < MAX_ROWS; i++) 
+            memory_copy(get_offset(0, i) + VIDEO_ADDRESS,
+                        get_offset(0, i-1) + VIDEO_ADDRESS,
+                        MAX_COLS * 2);
+
+        /* Blank last line */
+        char *last_line = get_offset(0, MAX_ROWS-1) + VIDEO_ADDRESS;
+        for (i = 0; i < MAX_COLS * 2; i++) last_line[i] = 0;
+
+        offset -= 2 * MAX_COLS;
+    }
+
+    set_cursor_offset(offset);
+    return offset;
+}
+
+int get_cursor_offset() {
+    /* Use the VGA ports to get the current cursor position
+     * 1. Ask for high byte of the cursor offset (data 14)
+     * 2. Ask for low byte (data 15)
+     */
+    port_byte_out(REG_SCREEN_CTRL, 14);
+    int offset = port_byte_in(REG_SCREEN_DATA) << 8; /* High byte: << 8 */
+    port_byte_out(REG_SCREEN_CTRL, 15);
+    offset += port_byte_in(REG_SCREEN_DATA);
+    return offset * 2; /* Position * size of character cell */
+}
+
+void set_cursor_offset(int offset) {
+    /* Similar to get_cursor_offset, but instead of reading we write data */
+    offset /= 2;
+    port_byte_out(REG_SCREEN_CTRL, 14);
+    port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset >> 8));
+    port_byte_out(REG_SCREEN_CTRL, 15);
+    port_byte_out(REG_SCREEN_DATA, (unsigned char)(offset & 0xff));
+}
+
+void clear_screen() {
+    int screen_size = MAX_COLS * MAX_ROWS;
+    int i;
+    char *screen = VIDEO_ADDRESS;
+
+    for (i = 0; i < screen_size; i++) {
+        screen[i*2] = ' ';
+        screen[i*2+1] = WHITE_ON_BLACK;
+    }
+    set_cursor_offset(get_offset(0, 0));
+}
+
+
+int get_offset(int col, int row) { return 2 * (row * MAX_COLS + col); }
+int get_offset_row(int offset) { return offset / (2 * MAX_COLS); }
+int get_offset_col(int offset) { return (offset - (get_offset_row(offset)*2*MAX_COLS))/2; }

20-interrupts-timer/drivers/screen.h

@@ -0,0 +1,19 @@
+#ifndef SCREEN_H
+#define SCREEN_H
+
+#define VIDEO_ADDRESS 0xb8000
+#define MAX_ROWS 25
+#define MAX_COLS 80
+#define WHITE_ON_BLACK 0x0f
+#define RED_ON_WHITE 0xf4
+
+/* Screen i/o ports */
+#define REG_SCREEN_CTRL 0x3d4
+#define REG_SCREEN_DATA 0x3d5
+
+/* Public kernel API */
+void clear_screen();
+void kprint_at(char *message, int col, int row);
+void kprint(char *message);
+
+#endif