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/* needs to stay the first line */
asm(".code16gcc\njmp $0, $main");
/* space for additional code */
char WRITE_CHARACTER_TTY = 0x0E;
// Syscall found here http://www.ctyme.com/intr/rb-0106.htm
void putc(char c) {
short command = WRITE_CHARACTER_TTY << 8 | c;
// volatile because there is no output, so the function might get optimized
// away
// clang-format off
asm volatile(
"int $0x10;"
::"a"(command)
);
// clang-format on
}
void print(char const *const str) {
for (int i = 0; str[i] != '\0'; ++i) {
putc(str[i]);
}
}
// Syscall found here http://www.ctyme.com/intr/rb-1754.htm
char getc() {
char ret;
asm volatile(
".no_key:"
"xor %%ax, %%ax;"
"mov $0x0100, %%ax;" // check for keystroke:
"int $0x16;" // http://www.ctyme.com/intr/rb-1755.htm
"jz .no_key;" // wait for a key
".done:"
"xor %%ax, %%ax;"
"mov $0x1000, %%ax;" // get keystroke: http://www.ctyme.com/intr/rb-1754.htm
"int $0x16;"
"mov %%al, %%bl;" // temp store char in bl
"mov $0400, %%ax;" // clear keyboard buffer:
"int $0x16;" // http://www.ctyme.com/intr/rb-1759.htm
: "=b"(ret)
:
: "ax");
return ret;
}
void sleep(short ms) {
long ys = ms * 1000;
short cx = ys >> 16;
short dx = ys;
// http://www.ctyme.com/intr/rb-1525.htm : Int 15/AH=86h bios wait
char ah = 0x86;
char al = 0x00;
short command = ah << 8 | al;
asm volatile("int $0x15;" : : "a"(command), "cx"(cx), "dx"(dx));
}
void main(void) {
print("Hello!");
print("\n\r > ");
while (1) {
putc(getc());
}
}
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