Using OpenOCD with the M4 MCU on the i.MX8M Mini

2025-04-01 19:01

Detlev Zundel

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Over the last few years, SoCs targeted at embedded GNU/Linux applications became heterogenous architectures. Instead of adding more identical copies of CPU cores (Cortex-A class), a small companion micro controller core (Cortex-M class) was added. Compared to the complex architecture of Cortex-A systems, including their multi-layer caches, those cores are usually deterministic and thus predestined for low-latency "real time" jobs. NXP's first such SoC is the i.MX6 Solo X device featuring an Cortex-M4 next to an Cortex-A9 core. The i.MX8 family moved the Cortex-A cores into the 64 bit world and there are different combinations of Cortex-M companion micro controllers, but all of them do feature them as they are pretty "cheap" in terms of die space and transistor count.

From what I can see, it is still uncommon to use those micro controllers in actual projects though. Today I want to take a short look on how to run simple programs on the Cortex-M4 of the i.MX8M Mini SoC, especially we will use the official i.MX8M Mini EVK.

dzu@krikkit:~$ openocd -f interface/jlink.cfg -f board/nxp_mcimx8m-evk.cfg -c 'init; imx8mq.m4 arp_examine'
Open On-Chip Debugger 0.11.0+dev-00585-g8b740af10 (2022-03-03-20:55)
Licensed under GNU GPL v2
For bug reports, read
        http://openocd.org/doc/doxygen/bugs.html
Info : J-Link EDU Mini V1 compiled Dec  7 2021 08:38:51
Info : Hardware version: 1.00
Info : VTarget = 1.791 V
Info : clock speed 1000 kHz
Info : JTAG tap: imx8mq.cpu tap/device found: 0x5ba00477 (mfg: 0x23b (ARM Ltd), part: 0xba00, ver: 0x5)
Info : imx8mq.a53.0: hardware has 6 breakpoints, 4 watchpoints
Info : starting gdb server for imx8mq.a53.0 on 3333
Info : Listening on port 3333 for gdb connections
Info : starting gdb server for imx8mq.m4 on 3334
Info : Listening on port 3334 for gdb connections
Info : gdb port disabled
Info : imx8mq.m4: Cortex-M4 r0p1 processor detected
Info : imx8mq.m4: target has 6 breakpoints, 4 watchpoints
Info : Listening on port 6666 for tcl connections
Info : Listening on port 4444 for telnet connections
Info : imx8mq.m4: external reset detected

zu@krikkit:/opt/src/git/mcuxsdk/examples/evkmimx8mm/demo_apps/hello_world/armgcc/debug ((MCUX_2.10.0))$ arm-none-eabi-gdb hello_world.elf
GNU gdb (GNU Arm Embedded Toolchain 10-2020-q4-major) 10.1.90.20201028-git
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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Reading symbols from hello_world.elf...
(gdb) target extended-remote localhost:3334
Remote debugging using localhost:3334
0x00000000 in ?? ()
(gdb) load
Loading section .interrupts, size 0x240 lma 0x1ffe0000
Loading section .resource_table, size 0x10 lma 0x1ffe0240
Loading section .text, size 0x39dc lma 0x1ffe0280
Loading section .ARM, size 0x8 lma 0x1ffe3c5c
Loading section .init_array, size 0x4 lma 0x1ffe3c64
Loading section .fini_array, size 0x4 lma 0x1ffe3c68
Loading section .data, size 0x68 lma 0x1ffe3c6c
Start address 0x1ffe0378, load size 15524
Transfer rate: 53 KB/sec, 2217 bytes/write.
(gdb)

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