A Chip Debug Module (CDM) is a specialized hardware block embedded in microcontrollers (MCUs), System-on-Chips (SoCs), or processors. It allows developers to observe, control, and diagnose the internal operation of a chip in real time, which is essential during development, testing, and debugging of embedded systems.

What is a Chip Debug Module?

A Chip Debug Module is an on-chip circuit that interacts with debugging tools (like JTAG/SWD, GDB, or IDEs) to:

Halt/resume program execution
Set breakpoints/watchpoints
Inspect and modify memory/registers
Trace instruction execution

Common protocols:

JTAG (Joint Test Action Group)
SWD (Serial Wire Debug – used in ARM Cortex-M)
BDM (Background Debug Mode – used in some Freescale MCUs)

Core Functions

Feature	Description
Breakpoints	Pause execution at specific code locations
Watchpoints	Monitor variable access (read/write)
Single-stepping	Execute code one instruction at a time
Register access	View/change CPU and peripheral registers
Memory inspection	Read/write RAM or flash in real-time
Program flow trace	Capture history of executed instructions (advanced)
Halt/Resume control	Pause/resume execution without resetting the system

Hardware Interface

To access a chip’s debug module, developers typically use:

ST-Link, J-Link, or CMSIS-DAP debuggers
IDE Integration: Keil, STM32CubeIDE, MPLAB X, IAR, PlatformIO, etc.
Connections: 4–6 pin JTAG or 2-pin SWD interface

Applications

1. Firmware Debugging

Track down runtime bugs like crashes, unexpected resets, or variable corruption.
Single-step through bootloaders or interrupt service routines (ISRs).

2. Performance Optimization

Analyze timing, bottlenecks, and memory usage using trace modules (e.g., ETM, ITM in ARM chips).

3. Real-Time Monitoring

Watch live variables, GPIO states, or ADC readings without stopping the chip.

4. Fault Diagnosis

Identify causes of hard faults, memory faults, or watchdog triggers using debug exception handlers.

5. Flash Programming

Upload firmware into flash memory directly through the debugger.

Example: STM32 Cortex-M Debug Module

ARM Cortex-M chips include CoreSight debug architecture with:

DWT (Data Watchpoint & Trace)
ITM (Instrumentation Trace Macrocell)
SWD/JTAG access
Debug Monitor Exception

These are accessed via STM32CubeIDE or tools like OpenOCD, ST-Link Utility, or Segger Ozone.

Security Considerations

Some systems disable the debug module in production to prevent reverse engineering.
Features like debug lock, readout protection (ROP), and secure boot limit access.

Summary

Pros	Cons
Speeds up development and debugging	Increases chip complexity
Enables low-level inspection and control	May introduce security risks if not protected
Essential for embedded system optimization	Requires external hardware debugger

Chip Debug Module and Its Application