> -----Original Message----- > From: Bithika Khargharia [mailto:bithika@xxxxxxxxx] > Sent: 24 March 2007 05:54 PM > To: Erik Mouw; Martyn Welch > Cc: kernelnewbies@xxxxxxxxxxxx > Subject: Re: OS Clock > > Thank you for both of your replies. Reading these registers > through the CPU does not make sense as you rightly pointed > out. I was thinking more along the lines of a DMA kind of > mechanism. I know that these registers have a memory-mapped > area that can be used to configure them from the OS and > program the counters to read different events. In a similar > manner, if it was possible to have the counters write to some > other memory-mapped area one could then read the data from > that memory-area after the experiments are done. Is that a > possibility? I really don't see how this would work. A DMA transfer would be able to transfer a block of contiguous data over a system bus. You are looking at transfering a number of registers repeatedly. Even if they are contiguously mapped, you still face the huge problem that you want to read them every nano second (i.e. with a frequency of 1GHz). Worse than that, you are now bringing a system bus into the equation. Even if you could utilse the bus 100% of the time to transfer the registers in question (i.e. not allow the CPU to use it at all - which would pretty much rule out doing anything useful with the processor), you wouldn't have the bandwidth to configure the operation and do the transfer under the timing conditions you are asking for (see Eric's reply about clock cycles, the system bus is slower...). Even if these transfers were possible, you will still require a processor somewhere capable of causing these transfers. Your main problem is that 1 nanosecond is a *really* short space of time, even for a fast microprocessor. Martyn ---- Martyn Welch Principal Software Engineer Radstone Digital Processing Part of GE Fanuc Embedded Systems Phone: +44 (0) 1327 322748 email: martyn.welch@xxxxxxxxxxxxxx web: www.radstone.com ________________________________________________________________________ This e-mail has been scanned for all viruses by Star.The service is powered by MessageLabs. ________________________________________________________________________ -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
