append-script: Add padding to Intel Hex record for old DAPLink compatibility

Author: microbit-carlos

src/__tests__/appended-script.spec.ts

@@ -17,7 +17,7 @@ describe('Inject Python code into Intel Hex string', () => {
       ':10E000004D50360066726F6D206D6963726F626984\n' +
       ':10E010007420696D706F7274202A0A646973706C61\n' +
       ':10E0200061792E7363726F6C6C282748656C6C6F16\n' +
-      ':0AE030002C20576F726C6421272921';
+      ':10E030002C20576F726C642127290000000000001B';
 
     const output: string = appendScriptToIntelHex(simpleIntelHex, pyCode);
 
@@ -34,7 +34,7 @@ describe('Inject Python code into Intel Hex string', () => {
       ':10E000004D50360066726F6D206D6963726F626984\n' +
       ':10E010007420696D706F7274202A0A646973706C61\n' +
       ':10E0200061792E7363726F6C6C282748656C6C6F16\n' +
-      ':0AE030002C20576F726C6421272921\n';
+      ':10E030002C20576F726C642127290000000000001B\n';
     const uicr: string =
       ':020000041000EA\n' +
       ':1010C0007CB0EE17FFFFFFFF0A0000000000E30006\n' +

src/appended-script.ts

@@ -28,6 +28,7 @@ const enum UserCodeBlock {
  * paste the Python Code
  */
 const HEX_INSERTION_POINT = ':::::::::::::::::::::::::::::::::::::::::::\n';
+const HEX_RECORD_DATA_LEN = 16;
 
 /**
  * Removes the old insertion line the input Intel Hex string contains it.
@@ -76,10 +77,11 @@ function getScriptFromIntelHex(intelHex: string): string {
  * @returns Byte array with the full User Code Block.
  */
 function createUserCodeBlock(dataBytes: Uint8Array): Uint8Array {
+  let blockLength = dataBytes.length + UserCodeBlock.HeaderLength;
+  // Old DAPLink versions need padding on the last record to fill the line
+  blockLength += HEX_RECORD_DATA_LEN - (blockLength % HEX_RECORD_DATA_LEN);
+  const blockBytes: Uint8Array = new Uint8Array(blockLength).fill(0x00);
   // The user script block has to start with "MP" marker + script length
-  const blockBytes: Uint8Array = new Uint8Array(
-    dataBytes.length + UserCodeBlock.HeaderLength
-  );
   blockBytes[0] = UserCodeBlock.HeaderStartByte0;
   blockBytes[1] = UserCodeBlock.HeaderStartByte1;
   blockBytes[2] = dataBytes.length & 0xff;