Update README.md

README.md

@@ -37,13 +37,29 @@ PRINT "Returned value in R0 was 42"
 
 ## What Does This Thumb-2 Machine Code Do?
 
-* The **first 32-bit word** (`00000000`) is the **entry point offset**, meaning execution starts at the first instruction.
+### `CSUB simple`
-* The **second 32-bit word** (`20420047`) encodes **two Thumb instructions**:
+- Starts the definition of a machine-code subroutine named `simple`.  
+- Tells the BASIC runtime that the following hex words are compiled machine code to execute when `simple()` is called.
 
-  * `movs r0, #42` (load immediate value 42 into register R0),
+### `00000000`
-  * `bx lr` (branch to link register, i.e., return).
+- The entry point offset for the CSUB.  
-* When `test()` is called, it runs these two instructions: loads 42 into R0 (commonly used to return values) and then returns.
+- A value of `0` indicates execution starts immediately at the next word.  
-* The BASIC program then continues and prints `Returned value in R0 was 42`.
+- This word is metadata only; it is **not executed** as machine code.
+
+### `00004770`
+- Encodes the Thumb instruction `BX LR` (Branch to Link Register).  
+- This instruction **returns immediately** from the subroutine to BASIC.
+
+### `END CSUB`
+- Marks the end of the CSUB block.  
+- Signals that the machine code definition is complete, and BASIC execution continues normally.
+
+### `simple()`
+- Calls the subroutine `simple`.  
+- Execution jumps to the CSUB, reads the entry point offset, executes the `BX LR` instruction, and immediately returns.
+
+### `PRINT " Returned successfully"`
+- Prints a message to the BASIC console to indicate the subroutine returned successfully.  
 
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