Add basic program loading, memory map, etc

src/chip8.rs

@@ -1,7 +1,103 @@
+// chip8.rs
+// Implementation of chip8 machine, registers, and memory makeup 
+
+use crate::util;
+
+// Memory map constants
+pub const PRGRM_START: usize = 512;
+pub const MAX_MEM_SIZE: usize = 4096;
+pub const MAX_PRG_SIZE: usize = 3584;
+
+// Instruction constants
+const INSTR_NOOP: u16 = 0x0000;
+const INSTR_EXIT: u16 = 0x00FD;
+
+#[derive(Debug)]
+struct EmulationState {
     // Miscellanious registers
-static mut program_counter: u16 = 0;
-static mut stack_ptr: u8 = 0;
+    program_counter: u16,
+    stack_ptr: u8,
     
     // General purpose registers
-static mut registers: [u8; 16] = [0; 16];
+    registers: [u8; 16],
 
+    // Memory Map:
+    // +---------------+= 0xFFF (4095) End of Chip-8 RAM
+    // |               |
+    // |               |
+    // |               |
+    // |               |
+    // |               |
+    // | 0x200 to 0xFFF|
+    // |     Chip-8    |
+    // | Program / Data|
+    // |     Space     |
+    // |               |
+    // |               |
+    // |               |
+    // +- - - - - - - -+= 0x600 (1536) Start of ETI 660 Chip-8 programs
+    // |               |
+    // |               |
+    // |               |
+    // +---------------+= 0x200 (512) Start of most Chip-8 programs
+    // | 0x000 to 0x1FF|
+    // | Reserved for  |
+    // |  interpreter  |
+    // +---------------+= 0x000 (0) Start of Chip-8 RAM
+    memory: [u8; 4096]
+}
+
+pub fn start_emulation(data: [u8; MAX_PRG_SIZE]) {
+    let mut state: EmulationState = EmulationState{
+        program_counter: 0,
+        stack_ptr: 0,
+        registers: [0; 16],
+        memory: [0; MAX_MEM_SIZE]
+    };
+
+    load_program(data, &mut state);
+    exec_program(&mut state);
+}
+
+// Load the program into virtual memory
+fn load_program(data: [u8; MAX_PRG_SIZE], state: &mut EmulationState) {
+    println!("Copying program data to memory");
+    for i in 0..MAX_PRG_SIZE {
+        state.memory[i+PRGRM_START] = data[i];
+    }
+}
+
+// Execute the program starting at the userspace address
+fn exec_program(state: &mut EmulationState) {
+    println!("Starting emulation");
+
+    let mut head_byte: u8;
+    let mut tail_byte: u8;
+    let mut instruction_tuple: (u8, u8);
+
+    for _i in PRGRM_START+usize::from(state.program_counter)..MAX_MEM_SIZE {
+        // Grab the first byte of instruction
+        head_byte = state.memory[PRGRM_START + usize::from(state.program_counter)];
+        state.program_counter += 1;
+        
+        // Grab the second byte of instruction
+        tail_byte = state.memory[PRGRM_START + usize::from(state.program_counter)];
+        state.program_counter += 1;
+        
+        instruction_tuple = (head_byte, tail_byte);
+
+        println!("0x{:02X?}{:02X?}", head_byte, tail_byte);
+
+        if util::u8_tuple_to_u16(instruction_tuple) == INSTR_EXIT {
+            println!("Read exit instruction, stopping emulation");
+            return;
+        }
+
+        if util::u8_tuple_to_u16(instruction_tuple) == INSTR_NOOP {
+            println!("Read no-op instruction, stopping emulation");
+            return;
+        }
+    }
+
+    
+}

src/main.rs

@@ -5,6 +5,7 @@ use std::process::exit;
 
 // Module imports
 mod util;
+mod chip8;
 
 fn main()
 {
@@ -31,8 +32,24 @@ fn main()
         
         if contents.is_ok()
         {
-            let _bytes: &Vec<u8> = &contents.expect("");
-            // let magic_num: &[u8] = &bytes[0..4];   
+            let file_data: &Vec<u8> = &contents.expect("");
+            if file_data.len() > chip8::MAX_PRG_SIZE.into() {
+                eprintln!("Error loading file, program size too large!");
+                exit(1);  
+            }
+            else if file_data.len() == 0 {
+                eprintln!("Error loading file, no program data found!");
+                exit(1);
+            }
+
+            let mut program: [u8; chip8::MAX_PRG_SIZE] = [0; chip8::MAX_PRG_SIZE];
+            for i in 0..file_data.len() {
+                program[i] = file_data[i];
+            }
+
+            println!("Read {} bytes of program data", file_data.len());
+            chip8::start_emulation(program);
+            
         }
     } else
     {

src/util.rs

@@ -1,3 +1,9 @@
 pub fn print_help() {
     print!("Usage: saltnvinegar [CHIP8_FILE]\n");
 }
+
+pub fn u8_tuple_to_u16(u8_in: (u8, u8)) -> u16 {
+    let head_byte: u16 = u16::from(u8_in.0) << 8;
+    let tail_byte: u16 = u16::from(u8_in.1);
+    return head_byte + tail_byte;
+}