Greetings all, I am a recent college grad with a new job and have been assigned to write a driver for a frame grabber that must meet certain real-time constraints. Since I have only a basic understanding of how all this stuff works, I have a few questions for the experts.
1. I more or less understand how one would go about writing a device driver in "normal" Linux, but it seems that writing an RTLinux driver is two-fold. First you have the real time part that actually deals with the hardware and getting data from that hardware into some data structure. Second, you have the non-real time portion that uses either shared memory or FIFOs to get the data out from the real time portion. I suppose to make the driver generic and reusable you'd need to write a sort of pseudo non-real time driver that holds all the ioctl commands. Is this assumption correct, or should the app simply pull data from the FIFOs/shared memory? What I am trying to understand is whether or not I should make a generic Linux driver to go along with my RTLinux driver or if I should simply embed communication with the real time side into the custom app we're making, since once you get the data into a FIFO or shared memory it's already in user space. 2. Exactly how to the FIFOs work? Let's say that I want to grab frames at 30Hz and the frames are 1k in size. I want to assure that I have a 1 second buffer between the real time side and the non-real time side, so I allocate a FIFO of size 30k. So now I can store 30 1k frames in the FIFO before it gets full, right? Okay, so what happens when it gets full? Does rtf_put() overwrite part of the FIFO or does it not do anything? 3. When I'm reading or writing to a shared memory buffer or to FIFOs I shouldn't run into one thread/process reading or writing at the same time unless those threads/processes are in the same "space," right? What I mean is that if I have a non-real time app accessing shared memory it should never read or write while a real time app is trying to read or write because RT apps get higher priority. If so, does this hold on SMP machines? Also, if a non-real time app was writing and a real time app needed to write to the same shared memory buffer, would it preempt the non-real time app before it got finished writing? 4. Are there any HOW-TO's out there with respect to RTLinux? I have read the documentation and examples that comes with RTLinux v3.1 and have gained a minimal understanding how things work, but if there are any more up-to-date resources I would very much like to read them. I am a sponge for knowledge! Thanks in advance for any help!! Brian Rivers _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com -- [rtl] --- To unsubscribe: echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED] -- For more information on Real-Time Linux see: http://www.rtlinux.org/
