MiV and printf to the Debugger Console

[rockoguido]

Working with a customer with a Bare Metal App on the Mi-V and there is no UART support. Is there a way to map printfs to the Debugger Console in Soft Console?

Looked around and no magic Macro jumped out at me..

Thx!
Dave

[nitindeshpande]

@rockoguido Do you mean that there is no UART IP used in the design and you want to transport the messages over debugger JTAG interface?

[AntonKrug]

I feels to me that you want semihosting. But maybe you could be interested of doing printf through the debugger. Where you do not need semihosting support, nor working uart.

And in the printf you can reference variables etc...

[JV73]

Hm - interesting. Would you need to apply this to every instance of printf in the code base ? Where does the output end up ? I tried this in SoftConsole 2021.3 with the 'first' printf in my program targeted to an RV32 implementation. I don't see the string that should have been printed in either the 'build console' or the 'debugger console' or a 'popup'.

[JV73]

I tried enabling 'ARM Semihosting' in the debugger settings, but again, I don't see an 'application console' or messages in either the build or debug console tabs of the debug perspective.

[JV73]

I'm beginning to get the feeling the SoftConsole OpenOCD implementation does not have RISC-V Semihosting support implemented, and likewise, the current miv_riscv_hal/stdio library does not contain hooks for semihosting stdin/stdout/stderr via the debugger. This would be a great enhancement as it is very common for an embedded ARM to support a 'virtual console' through the debugger (JTAG) without implementing hardware (UART) to bring it out of the chip.

[AntonKrug]

Not really for every printf instance as this can be applied to a application which doesn't even have printf at all. But you have to apply this from debuger so sharing code between co-workers will lose your dynamic-printf 'breakpoints'. You would have to apply it everywhere where you want the debuger to do the its printf, independetly if the there is a printf in the code or not.

The output is shown in Debuger Console:

Not sure about current state of OpenOCD, but when the RISC-V semihosting was introduced to OpenOCD, then at that time I was experimenting with it (just for fun), the Mi-V HAL was not supporting it, so I tested RISC-V boards from different vendors and with their HALs, where the semihosting worked. But that was long time ago and now not sure if the semihosting still works or not.

[JV73]

I've got this working on an Avalanche Board with SoftConsole v2021.3 You can define you own 'output buffer' and use sprintf(buf, fmt, ...) or your own print function to write a zero terminated string into the buffer, and then call sys_writes() [see attached] to send it to the GDB console via OpenOCD running under SoftConsole. This approach is 'relatively non-blocking' in that the action will auto-complete. Reading input from the GDB console is accomplished using the sys_readc() [see attached] function to poll for input characters one at a time. Currently, I find that this action will 'block' execution of the RISC-V code because the GDB console 'buffers' typed characters until the 'enter key' is pressed. Then each call to sys_readc() will return one character until the 'enter' character is read. Then a subsequent call to sys_readc() will again 'block' execution. I'm looking for a way to tell OpenOCD to turn-off character buffering in the GDB console - anyone know the right command ?
RV32-SemiHosting.zip

Note: I added a global variable that defaults to 'disable' the semi-hosting console interface at power-up/boot so that the RISC-V program can 'free run' at boot time. I added an ISR that is triggered by a push-button to 'enable' the interface after a debugger is attached, and an 'exit' command to again disable the interface before closing the debugger. That way - the 'main loop' can operate normally when the console is not active.

Note: if you get 'strange' results when printing to the GDB console via semi-hosting, make sure that you're GDB console preferences look something like this: