test(timing): compare prefetch cancellation with published observations

crates/gba-demos/examples/prefetch_cancellation.rs

@@ -0,0 +1,51 @@
+//! Diagnostic only: a matching boundary total does not make a timer mismatch pass.
+use std::process::ExitCode;
+
+use gba_demos::prefetch_probe::{measure, ProbeError, PUBLISHED_READ_DELTAS, WAITCNT_SETTINGS};
+
+fn run() -> Result<bool, ProbeError> {
+    eprintln!("Original ARM read probe; published reference: PrefetchAbuse 9ca57c13.");
+    eprintln!("Timer samples are unadjusted. This is not a run of the upstream ROM.");
+    println!("idle_cycles,waitcnt,published_delta,boundary_delta,timer_delta,boundary_matches,timer_matches");
+    let mut boundary_matches = 0;
+    let mut timer_matches = 0;
+    for (index, expected) in PUBLISHED_READ_DELTAS.into_iter().enumerate() {
+        for (waitcnt, expected) in WAITCNT_SETTINGS.into_iter().zip(expected) {
+            let control = measure(waitcnt, index as u8 + 1, false)?;
+            let read = measure(waitcnt, index as u8 + 1, true)?;
+            let boundary_delta = read.boundary_cycles as i64 - control.boundary_cycles as i64;
+            let timer_delta = i64::from(read.timer_sample) - i64::from(control.timer_sample);
+            let boundary_ok = boundary_delta == i64::from(expected);
+            let timer_ok = timer_delta == i64::from(expected);
+            boundary_matches += usize::from(boundary_ok);
+            timer_matches += usize::from(timer_ok);
+            println!(
+                "{},0x{waitcnt:04x},{expected},{boundary_delta},{timer_delta},{boundary_ok},{timer_ok}",
+                index + 1
+            );
+        }
+    }
+    let cases = PUBLISHED_READ_DELTAS.len() * WAITCNT_SETTINGS.len();
+    eprintln!(
+        "Boundary matches: {boundary_matches}/{cases}; timer matches: {timer_matches}/{cases}."
+    );
+    eprintln!(
+        "Full-buffer restart, Thumb, cartridge writes, and page boundaries are outside this probe."
+    );
+    Ok(boundary_matches == cases && timer_matches == cases)
+}
+
+fn main() -> ExitCode {
+    if std::env::args_os().len() != 1 {
+        eprintln!("prefetch_cancellation takes no arguments");
+        return ExitCode::from(2);
+    }
+    match run() {
+        Ok(true) => ExitCode::SUCCESS,
+        Ok(false) => ExitCode::FAILURE,
+        Err(error) => {
+            eprintln!("{error}");
+            ExitCode::from(2)
+        }
+    }
+}