From: "Tom Demmer" <DEMMER AT brain1 DOT lstm DOT ruhr-uni-bochum DOT de>
Organization:  Lehrstuhl Stroemungsmechanik, RUB
To: djgpp AT delorie DOT com
Date:          Mon, 28 Apr 1997 08:39:59 GMT-1
MIME-Version:  1.0
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Subject:       Need help on DMA transfer
Reply-to: Demmer AT LStM DOT Ruhr-Uni-Bochum DOT De
Message-ID: <5E6E9801EF3@brain1.lstm.ruhr-uni-bochum.de>
Precedence: bulk

Hi all,
I have (partially) ported the GPIB library from the Linux Lab Project 
to DJGPP. It is a lib to program IO-Cards that communicate with 
Voltmeters, Oscilloscopes and such things. These cards can be run in 
two modes, PIO or DMA. The PIO part is working, but I think DMA could 
be faster. So I have a few questions:

 - Can the DMA buffer be above 1 MB, or _must_ I transfer from/to
   DOS memory?
 - If I have to go over DOS mem, how can I ensure the buffer does not
   cross a 128kB boundary? Or is the information, DMA buffers must not
   cross such a boundary, outdated?

And the toughest thing ;-) this is from the Linux code:
I know what most of the functions are doing, but I don't have the 
slightest idea _how_:

   /* program dma controller */
   /* rwop->io_cnt is the # of bytes to xfer */
   /* rwop->io_pbuf is a pointer to the buffer
   ** to read/write from/to
   */
   cli();
   disable_dma( ibdma );                /* ibdma is the DMA channel */ 
   clear_dma_ff ( ibdma );              /* ???? */
   /* These ones are self-explaining, but how to do it? */
   set_dma_count( ibdma, rwop->io_cnt );
   set_dma_addr ( ibdma, rwop->io_pbuf);
   if (rwop->io_flags & IO_READ) {
      set_dma_mode( ibdma, DMA_MODE_READ );
   }
   else {
      set_dma_mode( ibdma, DMA_MODE_WRITE );
   }
   enable_dma( ibdma );/* enable Host side DMA transfers */
   sti();
   /*
   ** Let IO card initiate DMA
   */
   bdDMAstart(rwop);
   /*
   ** Wait until card finished or error
   */
   bdDMAwait(rwop, 0);
   /*
   ** Stop IO card and get amount xfered
   */
   resid = bdDMAstop(rwop);
   /*
   ** Disable DMA channel. How?
   */
   disable_dma( ibdma );
   return resid;

   
Any help appreciated, TIA.

Ciao
Tom

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  *  Thomas Demmer                     * Phone : +49 234 700 6434  *
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  *  Lehrstuhl fuer Stroemungsmechanik *                           *
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