vnf: add the 'Machine.halt_on_brk' field

This allows developers to use 'brk' as asserts which can then be
debugged. This is true by default but it can be turned off via the
--no-halting-brk option from runrom.

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>

3 files changed, 20 insertions, 1 deletions

diff --git a/crates/runrom/src/main.rs b/crates/runrom/src/main.rs
index 8f52f4a..9040261 100644
--- a/crates/runrom/src/main.rs
+++ b/crates/runrom/src/main.rs
@@ -16,6 +16,7 @@ struct Args {
     nasm: Option<PathBuf>,
     dump_memory: bool,
     until_address: u16,
+    halt_on_brk: bool,
 }
 
 fn print_help() {
@@ -26,6 +27,7 @@ fn print_help() {
     println!("  -f, --function\t\tRun the code by assuming it's a function.");
     println!("  -h, --help\t\t\tPrint this message and quit.");
     println!("  -n, --nasm-directory <PATH>\tPath to the .nasm/ directory.");
+    println!("  --no-halting-brk\t\tDo not halt execution after a brk instruction.");
     println!("  -s, --start\t\t\tAddress from where to start (default: reset vector).");
     println!("  -u, --until-address\t\tRun until the given address is met.");
     println!("  -v, --version\t\t\tPrint version information.");
@@ -130,6 +132,8 @@ fn parse_arguments() -> Args {
     let mut start = None;
     let mut until_address = None;
 
+    res.halt_on_brk = true;
+
     // Skip command name.
     args.next();
 
@@ -164,6 +168,9 @@ fn parse_arguments() -> Args {
                 }
                 None => die("you need to specify a file for the '-n/--nasm' flag".to_string()),
             },
+            "--no-halting-brk" => {
+                res.halt_on_brk = false;
+            }
             "-u" | "--until-address" => {
                 until_address = args.next();
                 if until_address.is_none() {
@@ -260,12 +267,14 @@ fn run(
     start: u16,
     end: u16,
     assume_function: bool,
+    halt_on_brk: bool,
     dump_memory: bool,
 ) -> Result<(), String> {
     let mut machine = Machine::from(file, start, MemoryPolicy::default())?;
 
     machine.verbose = true;
     machine.run_function_mode = assume_function;
+    machine.halt_on_brk = halt_on_brk;
 
     machine.until_address(end)?;
 
@@ -303,6 +312,7 @@ fn main() {
         start,
         args.until_address,
         args.assume_function,
+        args.halt_on_brk,
         args.dump_memory,
     ) {
         Ok(m) => m,
diff --git a/lib/vnf/src/lib.rs b/lib/vnf/src/lib.rs
index 61f117d..c9ae1a0 100644
--- a/lib/vnf/src/lib.rs
+++ b/lib/vnf/src/lib.rs
@@ -378,6 +378,10 @@ pub struct Machine {
 
     /// The status of both Joypads.
     joypads: [Joypad; 2],
+
+    /// Whether execution should be halted _after_ a 'brk' instruction no matter
+    /// what. The break mark will be set accordingly.
+    pub halt_on_brk: bool,
 }
 
 // Returns a vector of MemoryCell representing the RAM for a Machine, which
@@ -487,6 +491,7 @@ impl Machine {
             should_report_ppu: false,
             policy,
             joypads: [Joypad::default(), Joypad::default()],
+            halt_on_brk: true,
         })
     }
 
@@ -1220,6 +1225,10 @@ impl Machine {
                 let low = &(self.prg_rom[len - 2] as usize);
                 self.pc = high + low;
                 self.skip_pc = true;
+
+                if self.halt_on_brk {
+                    self.active = false;
+                }
             }
             InstructionIdentifier::Rti => {
                 self.pop_status_register()?;
diff --git a/scripts/test-e2e.sh b/scripts/test-e2e.sh
index 573a729..2dce6fb 100755
--- a/scripts/test-e2e.sh
+++ b/scripts/test-e2e.sh
@@ -284,7 +284,7 @@ exit_code=$((exit_code + $?))
 
 echo "test: runrom => stack.nes"
 ./target/debug/nasm -Werror -o tests/out/stack.nes tests/runrom/stack.s
-./target/debug/runrom --function --dump-memory tests/out/stack.nes > tests/out/stack.txt
+./target/debug/runrom --no-halting-brk --function --dump-memory tests/out/stack.nes > tests/out/stack.txt
 diff tests/out/stack.txt tests/expected/runrom/stack.txt
 exit_code=$((exit_code + $?))