USB_CDC output buffer status.

[rew]

I have several applications where my application on the STM32 provides an USB_CDC commandline interface to the user.

So during development I have a terminal program to type commands and see responses.

But then for "internal applications" I might want to automate something through the module I've created and "for now" I don't care about what's coming back.

I then send: "please do this, please do that" to the device, and 1) the characters are echoed back and 2) output is produced.

This tends to "lock up" the device after a while when the USB output buffer fills up: My input-processing (and echo-ing) process ends up in a "write" call that blocks.

Is there an api call that allows me to determine the status of the output buffer? If the output buffer is over say 25% full I want to stop echo-ing characters and output data. (If I do this say in the input processing thread, say after getting a new character, then I hope I don't accidentally activate this with normal interactive work: A command can still output say multiple buffers of data, and the user is unlikely to type a new command before the output buffer has been mostly cleared).

[Giovanni]

You could try a non blocking TIME_IMMEDIATE write or a write with a small timeout.

Giovanni

[rew]

OK! How do I instruct "chprintf" to do that?

[Giovanni]

You need to create a "stream" object performing writes with timeout internally, you may use memstream as a template, then pass your object to chprintf for output.

Giovanni