Skip to content

Instantly share code, notes, and snippets.

@sean3z
Last active December 30, 2022 01:29
Show Gist options
  • Save sean3z/ec62318e860b224007d50362a4b3089e to your computer and use it in GitHub Desktop.
Save sean3z/ec62318e860b224007d50362a4b3089e to your computer and use it in GitHub Desktop.
Example nibble parsing for Chip-8 emulator
pub fn emulate_cycle(&mut self) {
self.fetch_opcode();
self.execute_opcode();
// okay, PCs are much faster these days
// threw this cheeky delay in to slow things down
thread::sleep(time::Duration::from_micros(500));
}
fn fetch_opcode(&mut self) {
self.opcode = (self.memory[self.program as usize] as u16) << 8 | (self.memory[(self.program + 1) as usize] as u16);
}
fn execute_opcode(&mut self) {
match self.opcode & 0xf000 {
0x0000 => self.op_0xxx(),
0x1000 => self.op_1xxx(),
0x2000 => self.op_2xxx(),
// .. remaining opcodes
_ => not_implemented(self.opcode as usize, self.program)
}
}
// Clear the display or Return from subroutine
fn op_0xxx(&mut self) {
match self.opcode & 0x000F {
0x0000 => { self.display.clear() }
0x000E => {
self.stack_pointer -= 1;
self.program = self.stack[self.stack_pointer] as usize;
}
_ => { not_implemented(self.opcode as usize, self.program) }
}
self.program += 2;
}
// Jumps to address
fn op_1xxx(&mut self) { self.program = self.op_nnn() as usize; }
// Calls subroutine
fn op_2xxx(&mut self) {
self.stack[self.stack_pointer] = self.program as u16;
self.stack_pointer += 1;
self.program = self.op_nnn() as usize;
}
fn op_x(&self) -> usize { ((self.opcode & 0x0F00) >> 8) as usize }
fn op_y(&self) -> usize { ((self.opcode & 0x00F0) >> 4) as usize }
fn op_n(&self) -> u8 { (self.opcode & 0x000F) as u8 }
fn op_nn(&self) -> u8 { (self.opcode & 0x00FF) as u8 }
fn op_nnn(&self) -> u16 { self.opcode & 0x0FFF }
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment