openocd-jtag

用途

本技能用于指导代理完成 OpenOCD 的配置与使用，覆盖 JTAG 和 SWD 目标，包括：向微控制器烧录固件、连接 GDB 进行裸机调试、设置硬件观察点，以及配置 J-Link 和 CMSIS-DAP 适配器。

触发场景

如何用 OpenOCD 将 GDB 连接到 MCU
如何使用 OpenOCD 烧录固件
如何为 OpenOCD 设置 J-Link
JTAG 与 SWD 有什么区别
如何在 GDB 中设置硬件观察点
OpenOCD 报错 “Error: unable to find JTAG device” 如何修复

JTAG 与 SWD 对比

特性	JTAG	SWD（Serial Wire Debug）
引脚	4+（TCK、TMS、TDI、TDO、TRST）	2（SWCLK、SWDIO）
多目标	支持（菊花链）	不支持（单目标）
速度	最高 30 MHz	最高 10 MHz
可用性	完整 JTAG：Cortex-A/R、RISC-V	SWD：仅 Cortex-M
线缆成本	更复杂	更简单的 2 线

大多数 Cortex-M 微控制器同时支持两者。引脚数量受限时使用 SWD。

OpenOCD 配置

# 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 8000

# 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 ...

连接 GDB

# 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.elf

烧录固件

# 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"

硬件断点与观察点

软件断点（break）会用陷阱指令修补指令内存——在没有调试寄存器的情况下，无法在 flash 原地执行（execute-in-place）中工作。应改用硬件断点：

# 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 watchpoints

OpenOCD 命令参考

# 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 0

常见错误

错误	原因	修复
unable to find JTAG device	接口、线缆或供电错误	检查 USB 连接；给目标供电；验证接口配置
JTAG scan chain interrogation failed	目标配置错误或 SWD 模式错误	将配置与具体 MCU 匹配；尝试 transport select swd
flash 'stm32f4x' is not supported	目标错误	检查 MCU 型号；使用正确的 .cfg
Error: timed out while waiting for target halted	目标在运行，未暂停	monitor halt；检查 BOOT 引脚
Cannot access memory at address	MMU、内存保护或地址错误	检查 MPU 配置；使用正确的 flash/RAM 地址
Warn: target not examined yet	OpenOCD 未连接到目标	检查供电与连接

J-Link 配置

# 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（OpenOCD 的替代方案）：

# Segger's own GDB server
JLinkGDBServer -if SWD -device STM32L476RG -port 3333 &
arm-none-eabi-gdb -ex "target remote :3333" firmware.elf

技能介绍

用途