1 files changed, 12 insertions, 0 deletions

diff --git a/shell/src/lib.rs b/shell/src/lib.rs
index 3090776..b2c4a1b 100644
--- a/shell/src/lib.rs
+++ b/shell/src/lib.rs
@@ -722,6 +722,7 @@ write `{} <path> TIL <marker>`",
         "kill" => cmd_kill(&parsed),
         "demo" => cmd_demo(&parsed),
         "fault" => cmd_fault(),
+        "stall" => cmd_stall(&parsed),
         _ => term_err(&alloc::format!("unknown command: {}", cmd)),
     }
 }
@@ -819,6 +820,17 @@ fn cmd_fault() {
     }
 }
 
+/// Set the display-store stall (cycles per word) — diagnostics knob that
+/// simulates the per-write cost of an uncached real-GPU framebuffer so
+/// the preemptive scheduler races long scroll pushes like on real
+/// hardware.  `stall 0` disables (default; QEMU RAM framebuffers are
+/// instant).
+fn cmd_stall(p: &Parsed) {
+    let n: u32 = p.args.first().and_then(|a| a.parse().ok()).unwrap_or(0);
+    rsnix::gop::DISPLAY_STALL.store(n, core::sync::atomic::Ordering::Relaxed);
+    term_println(&alloc::format!("stall: display store stall = {}", n));
+}
+
 fn cmd_clear() {
     rsnix::gop::clear_screen();
 }