Flashing is the process of moving our program into the microcontroller's (persistent) memory. Once flashed, the microcontroller will executed the flashed program everytime it is powered on.
In this case, our
led-roulette program will be the only program in the
microcontroller memory. By this I mean that there's nothing else running on the
microcontroller: no OS, no "daemon", nothing.
led-roulette has full control
over the device.
Onto the actual flashing. First thing we need is to do is launch OpenOCD.
We did that in the previous section but this time we'll run the command inside a
temporary directory (
/tmp on *nix;
%TEMP% on Windows).
Make sure the F3 is connected to your laptop and run the following commands on a new terminal.
# *nix $ cd /tmp # Windows $ cd %TEMP% # Windows: remember that you need an extra `-s %PATH_TO_OPENOCD%\share\scripts` $ openocd \ -f interface/stlink-v2-1.cfg \ -f target/stm32f3x.cfg
NOTE Older revisions need to pass slightly different arguments to
openocd. Review this section for the details.
The program will block; leave that terminal open.
Now it's a good time to explain what this command is actually doing.
I mentioned that the F3 actually has two microcontrollers. One of them is used as a programmer/debugger. The part of the board that's used as a programmer is called ST-LINK (that's how STMicroelectronics decided to call it). This "ST-LINK" is connected to the target microcontroller using a Serial Wire Debug (SWD) interface (this interface is an ARM standard so you'll run into it when dealing with other Cortex-M based microcontrollers). This SWD interface can be used to flash and debug a microcontroller. The ST-LINK is connected to the "USB ST-LINK" port and will appear as an USB device when you connect the F3 to your laptop.
As for OpenOCD. It's a software that provides some services like a GDB server "on top" of USB devices that expose a debugging protocol like SWD or JTAG.
Onto the actual command: Those
.cfg files we are using instruct OpenOCD to
look for a ST-LINK USB device (
interface/stlink-v2-1.cfg) and to expect a
STM32F3XX microcontroller (
target/stm32f3x.cfg) to be connected to the
The OpenOCD output looks like this:
Open On-Chip Debugger 0.9.0 (2016-04-27-23:18) Licensed under GNU GPL v2 For bug reports, read http://openocd.org/doc/doxygen/bugs.html Info : auto-selecting first available session transport "hla_swd". To override use 'transport select <transport>'. adapter speed: 1000 kHz adapter_nsrst_delay: 100 Info : The selected transport took over low-level target control. The results might differ compared to plain JTAG/SWD none separate Info : Unable to match requested speed 1000 kHz, using 950 kHz Info : Unable to match requested speed 1000 kHz, using 950 kHz Info : clock speed 950 kHz Info : STLINK v2 JTAG v27 API v2 SWIM v15 VID 0x0483 PID 0x374B Info : using stlink api v2 Info : Target voltage: 2.919073 Info : stm32f3x.cpu: hardware has 6 breakpoints, 4 watchpoints
The "6 breakpoints, 4 watchpoints" part indicates the debugging features the processor has available.
I mentioned that OpenOCD provides a GDB server so let's connect to that right now:
$ arm-none-eabi-gdb -q target/thumbv7em-none-eabihf/debug/led-roulette Reading symbols from target/thumbv7em-none-eabihf/debug/led-roulette...done. (gdb)
This only opens a GDB shell. To actually connect to the OpenOCD GDB server, use the following command within the GDB shell:
(gdb) target remote :3333 Remote debugging using :3333 0x00000000 in ?? ()
OpenOCD's GDB server is listening on TCP port 3333 (localhost). This command is connecting to that port.
After entering this command, you'll see new output in the OpenOCD terminal:
Info : stm32f3x.cpu: hardware has 6 breakpoints, 4 watchpoints +Info : accepting 'gdb' connection on tcp/3333 +Info : device id = 0x10036422 +Info : flash size = 256kbytes
Almost there. To flash the device, we'll use the
load command inside the GDB
(gdb) load Loading section .text, size 0x6798 lma 0x8000000 Loading section .ARM.extab.text._ZN44_$LT$char$u20$as$u20$core..char..CharExt$GT$11encode_utf817h4f3134c02513b5e1E, size 0xc lma 0x8006798 Loading section .ARM.extab.text._ZN4core3fmt9Formatter11debug_tuple17hf0ed23ebdee33c00E, size 0xc lma 0x80067a4 Start address 0x8000194, load size 26544 Transfer rate: 21 KB/sec, 6636 bytes/write.
And that's it. You'll also see new output in the OpenOCD terminal.
Info : flash size = 256kbytes +Info : Unable to match requested speed 1000 kHz, using 950 kHz +Info : Unable to match requested speed 1000 kHz, using 950 kHz +adapter speed: 950 kHz +target state: halted +target halted due to debug-request, current mode: Thread +xPSR: 0x01000000 pc: 0x08000194 msp: 0x2000a000 +Info : Unable to match requested speed 8000 kHz, using 4000 kHz +Info : Unable to match requested speed 8000 kHz, using 4000 kHz +adapter speed: 4000 kHz +target state: halted +target halted due to breakpoint, current mode: Thread +xPSR: 0x61000000 pc: 0x2000003a msp: 0x2000a000 +Info : Unable to match requested speed 1000 kHz, using 950 kHz +Info : Unable to match requested speed 1000 kHz, using 950 kHz +adapter speed: 950 kHz +target state: halted +target halted due to debug-request, current mode: Thread +xPSR: 0x01000000 pc: 0x08000194 msp: 0x2000a000
Our program is loaded, let's debug it!