Hello,
I am implementing an USB stack for ARM machine maintained by the L4 microkernel. It works quite well at the moment - USB hubs and HID devices are working properly. However, there are few open issues there:
1. Since ARM machine I use does not provide cache snooping, i.e. I have to flush/invalidate the caches manually, I've attempted to use the l4_cache_dma_coherent function. It did worked to some degree, but it flushed/invalidated only *some* lines of cache within requested region, instead of *all* lines of cache. Since I've failed to trace the bug, I've extended sigma0 with new functionality - ability to map uncached memory. I still don't like my hack though and I would like to find an official way to either change the attributes (from cached to uncached) of given page, or have fully working l4_cache_dma_coherent.
2. The USB stack is a multithreaded app where I would like to have different servers (e.g. server for HID input events, server for mass storage devices). Unfortunately a server seemed to work only when started from the main thread. Why is it so? Was that my fault?
3. When the mass storage server receives either read or write call, it needs to map caller's memory in uncached manner. Moreover, USB stack needs *physical* address of the caller's buffer. How can I find that out?
with best regards, Michal.