stdio_semihosting: Initial include of Semihosting-based STDIO #13320

bergzand · 2020-02-09T11:59:26Z

Contribution description

This PR adds ARM Semihosting-based STDIO capabilities. It allows STDIO over SWD/JTAG, similar to the Segger RTT protocol, but without requiring the proprietary Jlink binaries or a Jlink programmer to function. Only ARM MCUs are supported (but I've heard rumors that RISC-V has something similar). The big downsides are that Semihosting is relative slow and that it requires an active debugging session (at all times) when it is enabled. This last bit because it throws breakpoint instructions for write and read requests from the host.

Currently the terminal used is OpenOCD in debugger mode. Maybe this can be refined at some point by not halting the CPU when starting the terminal, but that's for later.

Testing procedure

Use the provided test application to verify the functionality
Check the provided docs.

I haven't tested it with pyOCD. It is probably also possible to use pyOCD for this, but that can be included in a follow-up PR.

Issues/PRs references

None

benpicco · 2020-02-13T19:15:16Z

Hm, how does this work?
When I simply do a make flash term I end up in gdb but don't see any output from the terminal.

Segger J-Link

/home/benpicco/dev/RIOT/dist/tools/openocd/openocd.sh debug /home/benpicco/dev/RIOT/tests/sys_stdio_semihosting/bin/mlpa_tracker-v2/tests_sys_stdio_semihosting.elf
### Starting Debugging ###
Open On-Chip Debugger 0.10.0+dev-00955-gef23852f-dirty (2019-10-28-14:52)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
Reading symbols from /home/benpicco/dev/RIOT/tests/sys_stdio_semihosting/bin/mlpa_tracker-v2/tests_sys_stdio_semihosting.elf...
Remote debugging using :3333
0x00000986 in timer_init (tim=tim@entry=0, freq=freq@entry=1000000, cb=cb@entry=0xc05 <_periph_timer_callback>, 
    arg=arg@entry=0x0 <cortex_vector_base>) at /home/benpicco/dev/RIOT/cpu/sam0_common/periph/timer.c:101
101	    while (dev(tim)->CTRLA.bit.SWRST) {}
(gdb) c
Continuing.
ps
ps

edbg on samr21-xpro

/home/benpicco/dev/RIOT/dist/tools/openocd/openocd.sh debug /home/benpicco/dev/RIOT/tests/sys_stdio_semihosting/bin/samr21-xpro/tests_sys_stdio_semihosting.elf
### Starting Debugging ###
Open On-Chip Debugger 0.10.0+dev-00955-gef23852f-dirty (2019-10-28-14:52)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
Reading symbols from /home/benpicco/dev/RIOT/tests/sys_stdio_semihosting/bin/samr21-xpro/tests_sys_stdio_semihosting.elf...
Remote debugging using :3333
0xfffffffe in ?? ()
(gdb) c
Continuing.
at91samd.cpu -- clearing lockup after double fault

Program received signal SIGINT, Interrupt.
[Switching to Thread 1]
0xfffffffe in ?? ()
(gdb) c
Continuing.
at91samd.cpu -- clearing lockup after double fault

bergzand · 2020-02-13T19:21:24Z

When I simply do a make flash term I end up in gdb but don't see any output from the terminal.

😢

I'll check if I forgot something

bergzand · 2020-02-13T19:29:43Z

@benpicco on the samr21-xpro I can reproduce your issue. However if I restart the node from the OpenOCD session it somehow starts working. I'll see if I can make this work without having to restart the node.

kaspar030 · 2020-03-10T13:27:28Z

sys/stdio_semihosting/stdio_semihosting.c

+    /* Moves cmd and args to r0 and r1. Then triggers a breakpoint.
+     * Finally moves the results stored in r0 to result
+     */
+    __asm(


Suggested change

__asm(

__asm__(

kaspar030 · 2020-03-10T13:28:27Z

sys/include/stdio_semihosting.h

@@ -0,0 +1,103 @@
+/*


do these defines need to be exported? If not, it is fine to define them in stdio_semihosting.c.

kaspar030 · 2020-03-10T13:30:46Z

sys/stdio_semihosting/stdio_semihosting.c

+ssize_t stdio_read(void* buffer, size_t count)
+{
+    if (STDIO_SEMIHOSTING_RX) {
+        ssize_t read = 0;


please rename variable. Somehow my brain doesn't shadow read() as happily as the C compiler, especially in stdio context.

kaspar030 · 2020-04-14T07:16:00Z

Hm, this doesn't come with an automatic test, but I guess that's difficult? If so, we should at least blacklist it for all workers and add a comment.

kaspar030 · 2020-04-14T07:45:36Z

Hm, this doesn't come with an automatic test, but I guess that's difficult? If so, we should at least blacklist it for all workers and add a comment.

offline discussion, result: please add README.md.

bergzand · 2020-04-14T10:00:40Z

offline discussion, result: please add README.md.

Added a very concise readme

fjmolinas · 2020-06-02T11:01:35Z

@bergzand can you rebase this one?

bergzand · 2020-06-02T11:12:33Z

Rebased!

fjmolinas · 2020-06-02T11:15:56Z

Rebased!

You also seemed to have addressed a couple of the commetns I was going to make hahaha :D

fjmolinas

Some comments, I'll test asap.

sys/stdio_semihosting/stdio_semihosting.c

makefiles/tools/serial.inc.mk

fjmolinas · 2020-06-02T11:14:48Z

sys/include/stdio_semihosting.h

+ * `RIOT_TERMINAL` variable has to be set to `semihosting`:
+ *
+ * ```
+ * make term RIOT_TERMINAL=semihosting


You didn't add this to Makefile.include because of inclusion order right?

You mean to automatically setting the RIOT_TERMINAL based on whether stdio_semihosting is enabled? I honestly haven't tried it :D

It would work if USEMODULE is passe by the user or in the APPLICATION but not in a BOARD configuration, which kind of sucks.

sys/stdio_semihosting/stdio_semihosting.c

fjmolinas · 2020-06-02T11:26:02Z

It is indeed slow but works like a charm.

### Starting Debugging ###
Open On-Chip Debugger 0.10.0+dev-01100-g51dd4ce6-dirty (2020-03-03-15:33)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
Reading symbols from /home/francisco/workspace/RIOT/tests/sys_stdio_semihosting/bin/iotlab-m3/tests_sys_stdio_semihosting.elf...
Remote debugging using :3333
0x080008ba in _semihosting_raw (args=0x2000090c <main_stack+1180>, cmd=5)
    at /home/francisco/workspace/RIOT/sys/stdio_semihosting/stdio_semihosting.c:89
89	    return _semihosting_raw(0x05, args);
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/francisco/workspace/RIOT/tests/sys_stdio_semihosting/bin/iotlab-m3/tests_sys_stdio_semihosting.elf 
main(): This is RIOT! (Version: 2020.07-devel-872-g75e378-pr-13320)
STDIO semihosting test application
> help
keep_alive() was not invoked in the 1000ms timelimit. GDB alive packet not sent! (1646). Workaround: increase "set remotetimeout" in GDB
help
Command              Description
---------------------------------------
reboot               Reboot the node
version              Prints current RIOT_VERSION
pm                   interact with layered PM subsystem
ps                   Prints information about running threads.
>

sys/include/stdio_semihosting.h

fjmolinas · 2020-06-02T11:34:57Z

Hmm I checked the output with more details and there is:

keep_alive() was not invoked in the 1000ms timelimit. GDB alive packet not sent! (5570). Workaround: increase "set remotetimeout" in GDB
ps

makefiles/tools/serial.inc.mk

fjmolinas · 2020-06-02T12:44:49Z

I do not get the timeout on a samr21-xpro, usb-kw41z or nucleo-f103rb so it seems like its something related with the iotlab-m3 debugger.

fjmolinas · 2020-06-04T06:49:40Z

I do not have anymore comments here you can squash if @kaspar030 feels like his comments have been addressed as well!

bergzand · 2020-06-09T08:16:28Z

Squashed

fjmolinas

ACK on my side.

kaspar030

ACK from me, too.

bergzand · 2020-06-09T14:54:19Z

Thanks!

bergzand added the Type: new feature The issue requests / The PR implemements a new feature for RIOT label Feb 9, 2020

bergzand force-pushed the pr/stdio/semihosting branch 2 times, most recently from 1e7dc10 to 26d1b97 Compare February 9, 2020 13:28

bergzand requested a review from aabadie February 10, 2020 12:00

miri64 mentioned this pull request Feb 25, 2020

stdio: a layered / multiheaded approach to I/O #13469

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kaspar030 reviewed Mar 10, 2020

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kaspar030 requested changes Mar 10, 2020

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bergzand requested review from fjmolinas, leandrolanzieri, MichelRottleuthner and smlng as code owners March 12, 2020 12:10

kaspar030 added Area: sys Area: System Platform: ARM Platform: This PR/issue effects ARM-based platforms labels Apr 14, 2020

kaspar030 self-assigned this Apr 14, 2020

bergzand force-pushed the pr/stdio/semihosting branch from 3b66345 to 75e378f Compare June 2, 2020 11:11

fjmolinas reviewed Jun 2, 2020

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fjmolinas added the Reviewed: 3-testing The PR was tested according to the maintainer guidelines label Jun 2, 2020

aabadie reviewed Jun 2, 2020

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bergzand added 3 commits June 9, 2020 10:14

tools/openocd: add OPENOCD_DBG_EXTRA_CMD

aff18b9

stdio_semihosting: Initial include of Semihosting-based STDIO

99ca736

stdio_semihosting: Add shell-based test application

11ee5ff

bergzand force-pushed the pr/stdio/semihosting branch from 0c0f593 to 11ee5ff Compare June 9, 2020 08:16

fjmolinas approved these changes Jun 9, 2020

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kaspar030 approved these changes Jun 9, 2020

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kaspar030 added the CI: ready for build If set, CI server will compile all applications for all available boards for the labeled PR label Jun 9, 2020

kaspar030 merged commit 1ed0d65 into RIOT-OS:master Jun 9, 2020

bergzand deleted the pr/stdio/semihosting branch June 9, 2020 14:54

miri64 added this to the Release 2020.07 milestone Jun 24, 2020

stdio_semihosting: Initial include of Semihosting-based STDIO #13320

stdio_semihosting: Initial include of Semihosting-based STDIO #13320

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Contribution description

Testing procedure

Issues/PRs references

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