On Tue, 20 Nov 2001, Adolf Ahmad MS wrote:
> Hi David Olofson,
>
> Thank you for your nice reply.
>
> Now, I have the board-design as belows,
>
> Digital Data Stream(1 to 5Mbytes/s) ==> 64Kbytes FIFO (IDT7208 chip) ==> PPI
> Card on ISA[but possible we substitute with PCI such PCI-1751 or PCIO-24 or
> use EPP LPT Port) ==> PC PIII-833MHz==> Save to File
>
> I want to capture the Data Stream to files, and we prefer to do that on
> Linux OS. The problem is,
> 1. Capture Methode from modules
> 2. If we get data directly from user spaces(using ioperm), many data
> some time lost.
>
> Adolfo
>
> -----Original Message-----
> From: David Olofson [SMTP:[EMAIL PROTECTED]]
> Sent: Monday, November 19, 2001 3:58 AM
> To: [EMAIL PROTECTED]
> Subject: Re: [rtl] DMA programming
>
> On Sunday 18 November 2001 01:52, Adolf Ahmad MS wrote:
> > Dear All,
> >
> > I have one problem to acquire data stream with speed 1 Mbytes/s,
> so if
> > we use "Rtirq" (interrupt method) we will loss much data.
>
> Note that you if you're in control of what hardware you use, you
> don't
> *have* to handle one IRQ per sample. If there are FIFO buffers and
> prescalers, or the IRQs can be triggered by the half-full/half-empty
>
> signals from the FIFOs, you can pump a block of samples for each
> IRQ.
>
> You still get the port access overhead (unless you have memory
> mapped
> FIFO "ports"), but it might work...
>
>
> > If you have experience to acquire the high speed data using DMA
> single
> > or double buffering in Linux, would you like to send me the
> examples
>
> I haven't programmed serious DMA stuff since the days of the Amiga,
> and
> the last time I did it was under DOS for some SoundBlaster card,
> IIRC.
> So, sorry; no RTL examples.
>
>
> > (both "how to acquire the data stream from outside ?" and also
>
> Not quite following... Are you thinking about configuring the DAQ
> card,
> and/or setting up the DMA controller for the transfer?
>
> Very hardware dependant stuff (except for the part of the DMA done
> by the
> PC chipset) - you probably need to be more specific to get useful
> info.
>
>
> > " how to get the data from DMA memory " without loss any data).
>
> If you don't have double DMA buffers, cicular DMA buffers or DMA
> buffers
> + hardware FIFOs, there's no way to avoid missing a few samples. You
>
> *must* use hardware that one way or another cuts your ISR some
> slack. If
> the ISR starts up exactly when the DMA pointer wraps, and the ISR
> starts
> reading from the start of the DMA buffer, the first few bytes will
> already be overwritten by the time the ISR starts.
>
> What you usually can do, even without explicit hardware support, is
> to
> simulate a circular DMA buffer using an RTL oneshot timer thread
> triggered by the "DMA completion ISR". Have the ISR start reading in
> the
> middle, grabbing the last half of the DMA buffer. Then wait for the
> timer
> thread to wake up after approximately 50% of one period, to grab the
>
> first half of the buffer. That way, you'll always be reading at
> least
> half a buffer away from the DMA pointer, which gives you plenty of
> margin
> to handle the scheduling jitter.
>
> Of course, to make an "instant start" without dropping the first
> half DMA
> buffer entirely, you need to set up the delayed thread when you
> start the
> DMA, so that it can grab the first half of the buffer before the DMA
>
> wraps and starts overwriting the data.
>
>
> //David Olofson --- Programmer, Reologica Instruments AB
>
> .- M A I A -------------------------------------------------.
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