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README
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This example program sends some characters on USART2 on the
ST STM32L DISCOVERY eval board. (USART2 TX on PA2 @ 115200 8n1)
It can _ALSO_ use semihosting to use regular stdio via the attached debugger.
This expects you to be using gcc-arm-embedded from
https://launchpad.net/gcc-arm-embedded
Semihosting is a neat feature, but remember that your application will
NOT WORK standalone if you have semihosting turned on!
$ make ENABLE_SEMIHOSTING=0 will rebuild this image _without_ semihosting
Semihosting is supported in "recent"[1] OpenOCD versions, however, you need
to enable semihosting first! If you have not enabled semihosting, you
will receive a message like this:
(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program:
/home/karlp/src/libopencm3-examples/examples/stm32/l1/stm32l-discovery/usart-semihosting/usart-semihosting.elf
Program received signal SIGTRAP, Trace/breakpoint trap.
0x08000456 in initialise_monitor_handles ()
(gdb)
# Here we enable semi-hosting
(gdb) mon arm semihosting enable
semihosting is enabled
(gdb) continue
...
You should now see the semihosting output in the window running OpenOCD.
Size Notes
~~~~~~~~~~
Semihosting is basically free
# Without
$ arm-none-eabi-size usart-semihosting.elf
text data bss dec hex filename
29056 2212 60 31328 7a60 usart-semihosting.elf
# With
$ arm-none-eabi-size usart-semihosting.elf
text data bss dec hex filename
29832 2212 232 32276 7e14 usart-semihosting.elf
The large size here is because of printf being included regardless, see
nano.specs if you care about this, this data here is to show that semihosting
doesn't cost much at all.
[1] At least since OpenOcd version 0.8.0-dev-00011-g70a2ffa (2013-05-14-19:41)
possibly earlier.
ca926f00e0