Multithreading

The Synopsys DWC USB driver (for the Raspberry Pi) says this in its documentation

Threading
WUDEV Core must be run on an operating system that provides for multiple threads/processes. Threading can be implemented in many ways, even in embedded systems without an operating system. At the bare minimum, the system should be able to start any number of processes at any time to handle special work. It need not be a pre-emptive system. Process context can change upon a call to a blocking function. The hardware interrupt context that calls the module’s ISR, and process context must have a way to disable interrupts for a period of time to lock them out. If all of this exists, the functions in dwc_os.h related to threading should be able to be implemented with the defined behavior.

Any ideas how this kind of lightweight threading might be done on RISC OS? I think it might be possible to come up with something based on callbacks, but I’m not familiar with the intricacies. UnixLib has a pthread library (based on, I think, calling Wimp_Poll inside a transient callback) which I assume wouldn’t be suitable.

UnixLib has a pthread library (based on, I think, calling Wimp_Poll inside a transient callback) which I assume wouldn’t be suitable.

UnixLib’s library uses a callback triggered from a ticker event to manage thread preemption. Calling Wimp_Poll isn’t necessary, since all the threads run within the same Wimp task. I suspect that using a simple scheme like that won’t be suitable for the USB drivers. Firstly it could be a long time until callbacks get triggered, and secondly even if callbacks are triggering on time, one centisecond is a very long time when you’re dealing with a 480Mbps bus. One of the reasons SCSISoftUSB was so slow was that it was using a ticker event to schedule USB reads/writes.

I think RTSupport is the closest thing to what you need. Some care will be needed when interfacing with the USB stack (I can’t remember the exact rules, but I’m fairly certain that some calls are only safe to make from the foreground – i.e. via a callback), but all the internal threads and task queues that the Synopsys driver uses should be able to run off of RTSupport threads/tasks.

May I suggest that you take a look at the experiments I did some years ago, and which results archive URL currently is: http://habett.org/armada/logiciels/mthrea.zip ?
Clearly it is released as “a work in progress” (I met some difficulties in interfacing it to the Shared C Library and did not proceed working on it).
I’ll be happy to answer all queries and suggestions relating to them, given usual contingencies (mainly time and domain knowledge ;-) ).

HTHATS,
Benoît

I copied the archive to my personal Web site so now you can find it via: http://bgilon.free.fr/RISCOS/preview/mthrea.zip too.
Benoît

Hii,
Sir,
I am a fresher in IT Industry,i done Java,J2ee in my graduation course but i have lots of confusion in multithreading and some more in c embedded. but now i feel more clear concepts in embedded.
Thanks to all you to explain and give example to clear concepts.I am also done software testing training course it give me little bit clear about coding.

Hi. To avoid potential confusion, would you please be so kind as to consider confirming that you are programming under RISC OS? Thanks.