OpenOCD J-Link ST-Link Debug

Overview

Use this skill to debug probe sessions by separating physical wiring, probe firmware, target voltage, reset strategy, transport, target script, flash algorithm, and GDB behavior. Probe failures are often reset or adapter issues.

When To Use

Use this skill when:

• The user cannot connect, halt, reset, flash, erase, verify, or attach with

OpenOCD, J-Link, ST-Link, CMSIS-DAP, pyOCD, or GDB.

• The issue involves SWD/JTAG wiring, adapter speed, reset config, target

scripts, flash loaders, protected devices, semihosting, RTT, or multicore.

• The same firmware behaves differently under debugger and standalone boot.

Do not use this skill for application fault analysis after a stable debug session exists. Use the architecture-specific debug skill then. For flash download failures focused on erase/program/verify, use mcu-flashing-debug.

First Questions

Ask for:

• Probe model, firmware version, debugger tool, target MCU/SoC, board, and OS.
• Wiring: VTref, GND, SWDIO/TMS, SWCLK/TCK, nRST/SRST, SWO, and

power ownership.

• Exact command, the -f interface/*.cfg and -f target/*.cfg scripts,

adapter speed, transport select, and full log.

• Reset mode, boot pins, readout protection (STM32 RDP), low-power state, and

external flash.

• Whether connect-under-reset, halt-after-reset, or attach-to-running is needed.

Launch Reference

• ST-Link: openocd -f interface/stlink.cfg -f target/stm32f4x.cfg

(stlink.cfg is the hla driver; use target/stm32f1x.cfg, stm32h7x.cfg, nrf52.cfg etc. for other parts).

• J-Link: openocd -f interface/jlink.cfg -c "transport select swd" -f target/stm32f4x.cfg.
• CMSIS-DAP/DAPLink: openocd -f interface/cmsis-dap.cfg -c "transport select swd" -f target/stm32f1x.cfg.
• Force JTAG instead of SWD: -c "transport select jtag" (note stlink.cfg

hla only supports hla_swd/hla_jtag).

• Set speed before target script: -c "adapter speed 1000" (kHz; deprecated

alias adapter_khz). Pick a probe by serial with -c "adapter serial <SN>" (older: hla_serial).

• Default TCP ports: GDB 3333, Telnet monitor 4444, Tcl 6666.

Debug Workflow

1. Prove physical connection.

Check VTref, ground, cable length, pinout, SRST line, and whether the probe powers or only senses the target. In the log confirm a valid SWD DPIDR 0x2ba01477 (Cortex-M3/M4) or JTAG IDCODE, not a zero/failed read (SWD DPIDR 0x00000000 / Error connecting DP: cannot read IDR).

1. Lower the adapter speed.

Start with adapter speed 480 or lower, then raise only after IDCODE, halt, reset, and mdw reads are stable.

1. Pick the right reset strategy.

In the target/board cfg set reset_config, e.g. srst_only srst_nogate for connect-under-reset, or none separate. Then use reset halt / reset init / reset run. Add -c "reset_config connect_assert_srst" for locked or fast-sleeping parts.

1. Validate target scripts.

Confirm transport select, chip family cfg, TAP/DAP IDs (-expected-id on jtag newtap/swj_newdap, -dp-id for SWD multidrop), flash bank, and _TARGETNAME/work-area RAM. List cores with targets.

1. Separate attach from flash.

Enter the monitor with telnet localhost 4444, then init and reset halt. Read state with targets, reg, mdw 0x08000000 4, mdh, mdb; write with mww 0x40021000 0x01. Only then flash: program firmware.elf verify reset or flash write_image erase firmware.bin 0x08000000 / flash erase_sector 0 0 last / flash info 0. resume to run, dump_image out.bin 0x08000000 0x10000 to read back.

1. Add extras last.

Enable arm semihosting enable, SWO/tpiu, or RTT only after the base debug path is reliable (see RTT And Semihosting).

GDB Attach

arm-none-eabi-gdb firmware.elf
(gdb) target extended-remote localhost:3333
(gdb) monitor reset halt
(gdb) load
(gdb) monitor reg
(gdb) continue

Use target remote for a single-session attach, target extended-remote to allow reconnect. monitor <cmd> forwards any OpenOCD command (e.g. monitor reset init, monitor flash write_image erase firmware.bin).

RTT And Semihosting

• Semihosting: after halt run arm semihosting enable (optionally

arm semihosting_fileio enable); printf/puts output appears on the OpenOCD console once the firmware links libnosys/semihosting stubs.

• RTT: rtt setup 0x20000000 2048 "SEGGER RTT" then rtt start; expose a

channel with rtt server start 9090 0 and read it via telnet localhost 9090. Use rtt channels to confirm the control block was found. The ID string defaults to "SEGGER RTT".

Common Failures

• VTref is missing, so Error: target voltage may be too low or the probe

cannot sense target voltage.

• Adapter speed too high for early boot/low-power/long wires, giving a failed

DPIDR read (Error connecting DP: cannot read IDR), Error: init mode failed (unable to connect to the target), or SWD ack not OK.

• SRST not wired but the script uses reset_config srst_only; switch to

none/connect_assert_srst.

• Device is readout-protected or locked (Error: … cannot be programmed); for

STM32 clear RDP with stm32f4x unlock 0 / stm32f1x unlock 0 (mass-erases).

• Wrong target cfg selects the wrong flash bank or work-area RAM, so

flash write_image/program fails or verify mismatches.

• External QSPI/SPI flash needs a board-specific flash bank driver

(stmqspi, cfi), not the internal loader.

• hla (stlink.cfg) cannot do raw swd/jtag low-level commands or SWD

multidrop; use interface/stlink-dap.cfg or a J-Link/CMSIS-DAP v2 probe.

Verification

Before claiming the debug path works:

• State probe, tool, exact command, transport, adapter speed, and reset mode.
• Confirm SWD DPIDR/IDCODE, reset halt, targets shows halted, a reg

read, and an mdw memory read.

• Confirm program … verify reset or flash write_image plus verify when

flashing is required.

• Confirm standalone boot still works after reset run and power-cycle, i.e.

after debugger-specific settings.

Example

User:

OpenOCD 连 STM32 一直 timeout。

Agent:

1. Checks VTref, ground, SWD pins, SRST, and lowers adapter speed 480.
2. Retries with reset_config connect_assert_srst and the correct

target/stm32f4x.cfg, watching for SWD DPIDR.

1. Separates connection evidence (init, targets, mdw) from

program/flash write_image errors.