diff --git a/main.html b/main.html
index 4f2972e..dadac68 100644
--- a/main.html
+++ b/main.html
@@ -59,8 +59,10 @@
     const CAPABILITIES_UUID = 'c5f50003-8280-46da-89f4-6d8051e4aeef';
 
     // Command codes
-    const CMD_WRITE_USER_PROGRAM_META = 0x06;
-    const CMD_WRITE_USER_RAM = 0x03;
+    const CMD_WRITE_USER_PROGRAM_META = 0x06; // ✅ correct
+    const CMD_WRITE_USER_PROGRAM = 0x07; // writes to FLASH (button runnable)
+    const CMD_WRITE_USER_RAM = 0x03; // writes to RAM only
+    const CMD_START_USER_PROGRAM = 0x01; // triggers run immediately
 
     let device, server, cmdChar, maxDataSize = 20;
 
@@ -125,6 +127,17 @@
       }
     }
 
+    function crc32(buf) {
+      let crc = 0xFFFFFFFF;
+      for (let i = 0; i < buf.length; i++) {
+        crc ^= buf[i];
+        for (let j = 0; j < 8; j++) {
+          crc = (crc >>> 1) ^ (crc & 1 ? 0xEDB88320 : 0);
+        }
+      }
+      return (crc ^ 0xFFFFFFFF) >>> 0;
+    }
+
     async function upload() {
       try {
         const resp = await fetch('./main.mpy');
@@ -134,23 +147,31 @@
         log(`Uploading ${mpy.length} bytes...`);
         setStatus('Uploading...');
 
-        // Write program metadata: cmd(1) + size(4 LE)
+        // 1. Metadata
         const meta = new Uint8Array(5);
-        meta[0] = CMD_WRITE_USER_PROGRAM_META;
+        meta[0] = 0x06; // CMD_WRITE_USER_PROGRAM_META
         new DataView(meta.buffer).setUint32(1, mpy.length, true);
         await cmdChar.writeValueWithResponse(meta);
 
-        // Write program data in chunks: cmd(1) + offset(4 LE) + data
-        const chunkSize = maxDataSize - 5; // 1 byte cmd + 4 bytes offset
+        // 2. Flash chunks
+        const chunkSize = maxDataSize - 5;
         for (let offset = 0; offset < mpy.length; offset += chunkSize) {
           const chunk = mpy.slice(offset, offset + chunkSize);
           const packet = new Uint8Array(5 + chunk.length);
-          packet[0] = CMD_WRITE_USER_RAM;
+          packet[0] = 0x07; // CMD_WRITE_USER_PROGRAM (flash)
           new DataView(packet.buffer).setUint32(1, offset, true);
           packet.set(chunk, 5);
           await cmdChar.writeValueWithResponse(packet);
         }
 
+        // 3. Checksum
+        const checksum = crc32(mpy);
+        const cksPacket = new Uint8Array(5);
+        cksPacket[0] = 0x08; // CMD_WRITE_USER_PROGRAM_CHECKSUM
+        new DataView(cksPacket.buffer).setUint32(1, checksum, true);
+        await cmdChar.writeValueWithResponse(cksPacket);
+        log(`Checksum: 0x${checksum.toString(16)}`);
+
         setStatus('Upload complete');
         log('Upload complete. Press the hub button to run.');
       } catch (e) {
@@ -158,7 +179,16 @@
         log('Error: ' + e.message);
       }
     }
-
+    function onNotify(event) {
+      const data = new Uint8Array(event.target.value.buffer);
+      if (data[0] === 0x01) {
+        log('[stdout] ' + new TextDecoder().decode(data.slice(1)));
+      } else if (data[0] === 0x00) {
+        log('[status] Hub status code: ' + data[1]);  // 0x00 = idle, etc.
+      } else {
+        log('[event 0x' + data[0].toString(16) + '] ' + Array.from(data).join(','));
+      }
+    }
     async function disconnect() {
       if (device && device.gatt.connected) {
         device.gatt.disconnect();
diff --git a/main.mpy b/main.mpy
new file mode 100644
index 0000000..a54675f
Binary files /dev/null and b/main.mpy differ
diff --git a/main.py b/main.py
index d19b432..ede11d0 100644
--- a/main.py
+++ b/main.py
@@ -1,4 +1,6 @@
 from pybricks.hubs import PrimeHub
 from pybricks.parameters import Color
+from pybricks.tools import wait
 hub = PrimeHub()
-hub.light.on(Color.GREEN)
\ No newline at end of file
+hub.light.on(Color.GREEN)
+wait(1000)
\ No newline at end of file
diff --git a/main2.mpy b/main2.mpy
new file mode 100644
index 0000000..5cb11f6
Binary files /dev/null and b/main2.mpy differ