brados/kernel/brados.c

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C
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#include <stddef.h>
#include <stdint.h>
// Make sure we are using the right compiler
#if defined(__linux__)
#error "You are using the wrong compiler."
#endif
// Color constants
enum vgaColor
{
COLOR_BLACK = 0,
COLOR_BLUE = 1,
COLOR_GREEN = 2,
COLOR_CYAN = 3,
COLOR_RED = 4,
COLOR_MAGENTA = 5,
COLOR_BROWN = 6,
COLOR_LIGHT_GREY = 7,
COLOR_DARK_GREY = 8,
COLOR_LIGHT_BLUE = 9,
COLOR_LIGHT_GREEN = 10,
COLOR_LIGHT_CYAN = 11,
COLOR_LIGHT_RED = 12,
COLOR_LIGHT_MAGENTA = 13,
COLOR_LIGHT_BROWN = 14,
COLOR_WHITE = 15
};
uint8_t makeColor(enum vgaColor fg, enum vgaColor bg)
{
return fg | bg << 4;
}
uint16_t makeVGAEntry(char c, uint8_t color)
{
uint16_t c16 = c;
uint16_t color16 = color;
return c16 | color16 << 8;
}
size_t strlen(const char *str)
{
size_t len = 0;
while (str[len] != 0)
len++;
return len;
}
static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 24;
size_t terminalRow, terminalCol;
uint8_t terminalColor;
uint16_t *terminalBuf;
void terminalInit()
{
terminalRow = terminalCol = 0;
terminalColor = makeColor(COLOR_LIGHT_GREY, COLOR_BLACK);
terminalBuf = (uint16_t *) 0xB8000;
for (size_t x = 0; x < VGA_WIDTH; x++) {
for (size_t y = 0; y < VGA_HEIGHT; y++) {
const size_t index = y * VGA_WIDTH + x;
terminalBuf[index] = makeVGAEntry(' ', terminalColor);
}
}
}
void terminalSetColor(uint8_t color)
{
terminalColor = color;
}
void terminalPutEntryAt(char c, uint8_t color, size_t x, size_t y)
{
const size_t index = y * VGA_WIDTH + x;
terminalBuf[index] = makeVGAEntry(c, color);
}
void terminalScroll()
{
for (size_t i = 1; i < VGA_HEIGHT; i++) {
for (size_t j = 0; j < VGA_WIDTH; j++) {
const size_t index = i * VGA_WIDTH + j;
const size_t indexBelow = (i - 1) * VGA_WIDTH + j;
terminalBuf[indexBelow] = terminalBuf[index];
}
}
for (size_t i = 0; i < VGA_WIDTH; i++) {
const size_t index = (VGA_HEIGHT - 1) * VGA_WIDTH + i;
terminalBuf[index] = ' ';
}
}
void terminalPutChar(char c)
{
if (c == '\n')
terminalCol = VGA_WIDTH - 1;
else
terminalPutEntryAt(c, terminalColor, terminalCol, terminalRow);
if (terminalCol++ == VGA_WIDTH) {
terminalCol = 0;
if (terminalRow++ == VGA_HEIGHT) {
terminalRow--;
terminalScroll();
}
}
}
void terminalWriteString(const char *data)
{
size_t dataLen = strlen(data);
for (size_t i = 0; i < dataLen; i++)
terminalPutChar(data[i]);
}
void brados_main()
{
terminalInit();
terminalWriteString("Welcome to BRaDOS!\n");
}