Como usar
- Copie o comando e verifique o pacote antes de instalar no seu ambiente de agente.
- Consulte no original as ferramentas, credenciais e ambientes necessários.
- Descreva os dados de entrada e a entrega esperada; confira a saída com as fontes.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill openocd-jtagAntes de começar
- A instalação não inclui assinatura de modelo, franquia API ou acesso aos seus arquivos.
- Estrelas e instalações indicam atividade, não um teste independente de qualidade ou segurança.
Documento original do Skill
Renderizado do repositório de origem, preservando títulos, exemplos, código, tabelas, links e imagens.
OpenOCD / JTAG Debugging
Purpose
Guide agents through configuring OpenOCD for JTAG and SWD targets, flashing firmware to microcontrollers, attaching GDB for bare-metal debugging, setting hardware watchpoints, and configuring J-Link and CMSIS-DAP adapters.
Triggers
- "How do I connect GDB to my MCU with OpenOCD?"
- "How do I flash firmware using OpenOCD?"
- "How do I set up J-Link with OpenOCD?"
- "What's the difference between JTAG and SWD?"
- "How do I set a hardware watchpoint in GDB?"
- "OpenOCD says 'Error: unable to find JTAG device' — how do I fix it?"
Workflow
1. JTAG vs SWD
| Feature | JTAG | SWD (Serial Wire Debug) |
|---|---|---|
| Pins | 4+ (TCK, TMS, TDI, TDO, TRST) | 2 (SWCLK, SWDIO) |
| Multi-target | Yes (daisy chain) | No (one target) |
| Speed | Up to 30 MHz | Up to 10 MHz |
| Availability | Full JTAG: Cortex-A/R, RISC-V | SWD: Cortex-M only |
| Cable cost | More complex | Simpler 2-wire |
Most Cortex-M microcontrollers support both. Use SWD when pin count is limited.
2. OpenOCD configuration
tcl
# openocd.cfg — CMSIS-DAP (ST-Link v2, DAPLink)
source [find interface/cmsis-dap.cfg]
source [find target/stm32f4x.cfg]
adapter speed 4000 # kHz
# For SWD explicitly
transport select swd
# J-Link adapter
source [find interface/jlink.cfg]
jlink serial 123456789 # optional: select by serial
source [find target/nrf52.cfg]
adapter speed 8000bash
# Run OpenOCD (keeps running, serves GDB on port 3333)
openocd -f openocd.cfg
# Common interface config files
ls $(openocd --help 2>&1 | grep "scripts" | head -1)/interface/
# cmsis-dap.cfg, jlink.cfg, ftdi/olimex-arm-usb-ocd.cfg, stlink.cfg ...
# Common target config files
ls $(openocd --help 2>&1 | grep "scripts" | head -1)/target/
# stm32f4x.cfg, nrf52.cfg, esp32.cfg, rp2040.cfg, at91sam4s.cfg ...3. Connecting GDB
bash
# In terminal 1: start OpenOCD
openocd -f openocd.cfg
# In terminal 2: start GDB
arm-none-eabi-gdb firmware.elf
# GDB commands
(gdb) target extended-remote :3333 # connect to OpenOCD
(gdb) monitor reset halt # reset and halt target
(gdb) load # flash ELF to target
(gdb) monitor reset init # re-initialize after flash
(gdb) break main # set software breakpoint
(gdb) continue
# One-liner for quick debugging
arm-none-eabi-gdb -ex "target extended-remote :3333" \
-ex "monitor reset halt" \
-ex "load" \
-ex "break main" \
-ex "continue" \
firmware.elf4. Flashing firmware
bash
# Flash via OpenOCD telnet interface
telnet localhost 4444
# OpenOCD telnet commands
> reset halt
> program firmware.elf verify reset
> exit
# Or via GDB
(gdb) monitor flash write_image erase firmware.bin 0x08000000
(gdb) monitor reset run
# Flash only (no debug) — script mode
openocd -f openocd.cfg \
-c "program firmware.elf verify reset exit"
# For raw binary
openocd -f openocd.cfg \
-c "program firmware.bin 0x08000000 verify reset exit"5. Hardware breakpoints and watchpoints
Software breakpoints (break) patch instruction memory with trap instructions — they don't work in flash-execute-in-place without debug registers. Use hardware breakpoints instead:
bash
# Hardware breakpoint (uses debug register, limited count: 4-8 on Cortex-M)
(gdb) hbreak function_name
(gdb) hbreak *0x08001234
# Hardware watchpoint — triggers on memory read/write
(gdb) watch global_variable # write watchpoint
(gdb) rwatch some_buffer # read watchpoint
(gdb) awatch sensor_value # read OR write watchpoint
# List breakpoints/watchpoints
(gdb) info breakpoints
# Cortex-M typically has: 4–8 hardware breakpoints, 2–4 watchpoints6. OpenOCD commands reference
bash
# Via telnet (port 4444) or GDB monitor
monitor reset halt # reset and hold at reset vector
monitor reset init # reset and run init scripts
monitor reset run # reset and run freely
monitor halt # halt running target
monitor resume # resume execution
monitor mdw 0x20000000 # memory display word at address
monitor mww 0x40021000 0x1 # memory write word
monitor reg r0 # read register
monitor arm disassemble 0x08000000 16 # disassemble 16 instructions
# Flash operations
monitor flash list
monitor flash erase_sector 0 0 0 # erase sector 0
monitor flash write_bank 0 firmware.bin 07. Common errors
| Error | Cause | Fix |
|---|---|---|
unable to find JTAG device | Wrong interface, cable, or power | Check USB connection; power target; verify interface config |
JTAG scan chain interrogation failed | Wrong target config or bad SWD mode | Match config to exact MCU; try transport select swd |
flash 'stm32f4x' is not supported | Wrong target | Check MCU part number; use correct .cfg |
Error: timed out while waiting for target halted | Target running, not halted | monitor halt; check BOOT pins |
Cannot access memory at address | MMU, memory protection, or wrong address | Check MPU config; use correct flash/RAM address |
Warn: target not examined yet | OpenOCD not connected to target | Check power and connections |
8. J-Link configuration
tcl
# openocd.cfg for J-Link
source [find interface/jlink.cfg]
jlink usb 0 # use first J-Link found
transport select swd # or jtag
adapter speed 4000
source [find target/stm32l4x.cfg]J-Link GDB Server (alternative to OpenOCD):
bash
# Segger's own GDB server
JLinkGDBServer -if SWD -device STM32L476RG -port 3333 &
arm-none-eabi-gdb -ex "target remote :3333" firmware.elfRelated skills
- Use
skills/embedded/freertosfor FreeRTOS-aware debugging with OpenOCD - Use
skills/embedded/zephyrfor Zephyr'swest debugintegration - Use
skills/debuggers/gdbfor GDB session management - Use
skills/embedded/linker-scriptsfor understanding memory map for flash addresses
