diff --git a/crsn/src/asm/parse/parse_data.rs b/crsn/src/asm/parse/parse_data.rs
index ce2f5dc..8d796d9 100644
--- a/crsn/src/asm/parse/parse_data.rs
+++ b/crsn/src/asm/parse/parse_data.rs
@@ -6,6 +6,7 @@ use crate::asm::data::{DataDisp, Rd, RdData, reg, Wr, WrData};
 use crate::asm::data::literal::Label;
 use crate::asm::error::CrsnError;
 use crate::asm::parse::sexp_expect::expect_string_atom;
+use std::borrow::Cow;
 
 /// Parse a label
 pub fn parse_label(name: Option<Sexp>) -> Result<Label, CrsnError> {
@@ -47,12 +48,17 @@ pub fn parse_data_disp(tok: Option<Sexp>) -> Result<DataDisp, CrsnError> {
 }
 
 pub fn parse_u64(literal: &str) -> anyhow::Result<u64> {
-    if let Some(hex) = literal.strip_prefix("0x") {
+    let mut without_underscores = Cow::Borrowed(literal);
+    if without_underscores.contains('_') {
+        without_underscores = without_underscores.replace('_', "").into();
+    }
+
+    if let Some(hex) = without_underscores.strip_prefix("0x") {
         Ok(u64::from_str_radix(hex, 16)?)
-    } else if let Some(hex) = literal.strip_prefix("0b") {
+    } else if let Some(hex) = without_underscores.strip_prefix("0b") {
         Ok(u64::from_str_radix(hex, 2)?)
     } else {
-        Ok(u64::from_str_radix(literal, 10)?)
+        Ok(u64::from_str_radix(&without_underscores, 10)?)
     }
 }
 
diff --git a/crsn/src/builtin/defs.rs b/crsn/src/builtin/defs.rs
index b74a6f9..566e6c8 100644
--- a/crsn/src/builtin/defs.rs
+++ b/crsn/src/builtin/defs.rs
@@ -8,6 +8,10 @@ pub enum BuiltinOp {
     Nop,
     /// Stop execution
     Halt,
+    /// Sleep
+    Sleep {
+        micros: Rd,
+    },
     /// Mark a jump target.
     Label(Label),
     /// Jump to a label
diff --git a/crsn/src/builtin/exec.rs b/crsn/src/builtin/exec.rs
index ba0fb6b..ad5f08d 100644
--- a/crsn/src/builtin/exec.rs
+++ b/crsn/src/builtin/exec.rs
@@ -6,6 +6,7 @@ use crate::module::{EvalRes, OpTrait};
 use crate::runtime::fault::Fault;
 use crate::runtime::frame::StackFrame;
 use crate::runtime::run_thread::{state::RunState, ThreadInfo};
+use std::time::Duration;
 
 impl OpTrait for BuiltinOp {
     fn execute(&self, info: &ThreadInfo, state: &mut RunState) -> Result<EvalRes, Fault> {
@@ -137,6 +138,9 @@ impl OpTrait for BuiltinOp {
                 let x = state.read(*src)?;
                 state.frame.status.load(x);
             }
+            BuiltinOp::Sleep { micros } => {
+                std::thread::sleep(Duration::from_micros(state.read(*micros)?))
+            }
             BuiltinOp::Drop(obj) => {
                 let x = state.read(Rd::new(RdData::Register(obj.reg())))?;
 
diff --git a/crsn/src/builtin/parse.rs b/crsn/src/builtin/parse.rs
index ff34ec9..bbae512 100644
--- a/crsn/src/builtin/parse.rs
+++ b/crsn/src/builtin/parse.rs
@@ -38,6 +38,12 @@ impl CrsnExtension for BuiltinOps {
                 BuiltinOp::Halt
             }
 
+            "sleep" => {
+                BuiltinOp::Sleep {
+                    micros: args.next_rd()?,
+                }
+            }
+
             "j" => {
                 let dest = parse_label(args.next())?;
                 BuiltinOp::Jump(dest)
diff --git a/launcher/src/main.rs b/launcher/src/main.rs
index 0e34b8d..29124b0 100644
--- a/launcher/src/main.rs
+++ b/launcher/src/main.rs
@@ -77,29 +77,29 @@ fn main() {
     let program = "
     (
         (main
-            (sc-init 640 480)
+            (sc-init 800 600)
             (sc-opt 1 0) ; auto blit
             (sc-opt 2 60) ; frame rate
 
-            (ld r0 39) ; x
+            (ld r0 5) ; x
             (ld r1 0) ; y
 
             (ld r2 1) ; dx
             (ld r3 1) ; dy
 
-            (ld r5 0xffffff)
+            (ld r5 0x3300ff)
 
             (:loop)
-            (add r5 0x010001)
+            (add r5 0x000001)
             (and r5 0xffffff)
             (sc-px r0 r1 r5)
-            (sc-blit 0)
             (add r0 r2)
             (add r1 r3)
-            (cmp r0 639 (eq? (ld r2 -1)))
+            (cmp r0 799 (eq? (ld r2 -1)))
             (cmp r0 0 (eq? (ld r2 1)))
-            (cmp r1 479 (eq? (ld r3 -1)))
+            (cmp r1 599 (eq? (ld r3 -1)))
             (cmp r1 0 (eq? (ld r3 1)))
+            (sc-blit 0)
             (j :loop)
         )
     )