On 2011-06-05 11:28, Nicholas Mc Guire wrote: > On Sun, 05 Jun 2011, Armin Steinhoff wrote: > >> Nicholas Mc Guire wrote: >>> On Sat, 04 Jun 2011, Monica Puig-Pey wrote: >>> >>>> Hello, >>>> I'm studying how to develop drivers in a real time OS and how do they >>>> work. I'm using Ubuntu 10.04 with the 2.6.31-11-rt patch installed. >>>> I would like to know the priority when executing open(), read(), write() >>>> and close() operations. >>>> In my example the thread which is using the driver runs with 10 RTPRIO, >>>> but I don't know what happens in kernel context with the priority when >>>> running the I/O operations. >>>> Thank you for your help, I don't know where to learn about this. >>>> >>> [] >>> Also when using bottom half mechanisms you need to take into account the >>> priority of the kernel thread that manages the defered work items, so >>> rt-drivers may have a different structure than normal drivers. >> >> That's the reason why I prefer UIO based user space drivers ! >> > ...and how to resolve DMA ? if DMA were resolved cleanly I would agree. Regarding that limitation, there is some hope: "next-generation" UIO is called VFIO. Useful for exclusively assigning virtual PCI functions of network adapters etc. to user space stacks or hypervisors like QEMU/KVM (for device pass-through). But it's not mainline yet. And it obviously requires an IOMMU. But the key point remains: "exclusively". Anything else cannot be modeled efficiently via UIO or VFIO. Jan
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