Mastering APM32: Common Commands for J-Link Commander

APM32 MCU runaway? Crash? Hardfault?

Don’t know what to do when encountering these unexpected scenarios? An expert would think of using J-Link commander to query information, can you? Today, I will introduce several common commands for the J-Link commander tool to help you master the APM32 chip smoothly.

1. mem : Read memory by byte

Command format: mem <address> <number of bytes>.For example, with the APM32F411 chip, to read the RCC clock control & status register at address 0×40023800+0×74, you would enter: mem 0×40023874 4.

2. mem32 : Read memory by word (4 bytes)

Command format: mem32 <address> <number of words>.For example, with the APM32F411 chip, to read the RCC clock control & status register at address 0×40023800+0×74, you would enter: mem32 0×40023874 1.

3. W4 : Write memory by word (4 bytes)

Command format: W4 <address> <data to write>.For example, with the APM32F411 chip, to write the data 0xA5A5A5A5 to the SRAM address 0×20000100, you would enter: W4 0×20000100 0xA5A5A5A5.

4. h : Halt

This stops the CPU execution. After entering this command, you can check information such as the PC pointer.

5. g : Go

The CPU starts running at full speed after this command is entered. If your development board has an LED, you will see the program running and the light blinking.

6. s : Single Step

When this command is entered, the CPU will execute one assembly instruction. (Note: The single-step command can only be used when the CPU is in a Halt state. This means you must call the “h” command before using single-step.)

7. r : Reset CPU

Entering this command will cause the MCU to reset, and the program will restart from the beginning.

Summary of common commands:

• usb: Connect to the target board
• r: Restart the target board
• halt: Stop the program running on the CPU
• loadbin: Load an executable binary file
• g: Jump to the code segment address and execute
• s: Single step execution (for debugging)
• setpc: Set the value of the PC register (for debugging)
• setbp: Set a breakpoint
• Regs: Read the register set; this command displays all registers
• wreg: Write to a register
• mem: Read memory
• w4: Write memory
• power off mmu: Disable the MMU, which is very important for bare-metal debugging
• w4 cpsr, 0×0000001f: Switch to system mode
• speed: Set the JTAG transmission speed
• rce 0, c0, c0, 0: Set the first register of CP15 to 0

Less common commands:

Here are some less common commands for those who are interested:

• ite: Read 32-bit items from memory. Syntax: w4 <addr>, <num> (reads 32 bytes from memory)
• wm: Write test words. Syntax: wm
• is: Identify the length of the scan chain select register
• ms: Measure the length of the scan chain. Syntax: ms
• mr: Measure RTCK reaction time. Syntax: mr
• q: Quit
• qc: Close J-Link connection and quit
• r: Reset target (RESET)
• rx: Reset target (RESET) with delay. Syntax: rx <delay>
• RSetType: Set the current reset type. Syntax: RSetType <type>
• Regs: Display contents of registers
• wreg: Write to a register. Syntax: wreg <RegName>, <Value>
• SetBP: Set a breakpoint. Syntax: SetBP <addr> [A/T] [S/H]
• SetWP: Set a watchpoint. Syntax: SetWP <addr> [R/W] [<Data> [<A-Mask>]]
• ClrBP: Clear a breakpoint. Syntax: ClrBP <BPHandle>
• ClrWP: Clear a watchpoint.
• VCatch: Write vector catch. Syntax: VCatch <value>
• loadbin: Load a binary file into target memory. Syntax: loadbin <filename>, <addr>
• savebin: Save target memory into a binary file. Syntax: savebin <filename>, <addr>, <numbytes>
• SetPC: Set the PC to a specified value. Syntax: SetPC <addr>
• le: Change to little-endian mode
• be: Change to big-endian mode
• log: Enable logging to a file. Syntax: log <filename>