DMA : numder of transfers

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2 total messages Started by Mats Astrom Thu, 01 Oct 1992 07:39

#671

Author: Mats Astrom
Date: Thu, 01 Oct 1992 07:39

53 lines
2859 bytes

While doing DMA-transfer it's possible to read the number of transfers done
by reading a specific register of the DMA-circuit. I've manage to do so but
the result seem to be somewhat instable ! The instability is due to reads of
the register in the middle of a transfer, isn't it ????
Assuming I'm setting up everthing correctly, how do I read the number of
transferred bytes to get the correct value every time ?????

I program in TP 6.0, with the following declarations the code is:

BTW, I'm doing integer ( 2 bytes ) transfers, see odd(lobyte1) below !

   lobyte1,
   lobyte2,
   hibyte1,
   hibyte2  : byte;

   DMACountReg = $03; { byte Count, ch1 }

    version 1:
                      {--- check how far DMA has gone ---}
                      repeat
                         lobyte1 := port[DMACountReg];
                         hibyte1 := port[DMACountReg];
                         lobyte2 := port[DMACountReg];
                         hibyte2 := port[DMACountReg];
                      until odd(lobyte1) and
                            (hibyte2=hibyte1) and
                            (lobyte2=lobyte1);
    version 2:
                      {--- check how far DMA has gone ---}
                      repeat
                         lobyte1 := port[DMACountReg];
                         hibyte1 := port[DMACountReg];
                         lobyte2 := port[DMACountReg];
                         hibyte2 := port[DMACountReg];
                      until odd(lobyte1) and ( ( (hibyte2=hibyte1) and
                                                 (lobyte2<=lobyte1) ) or
                                              ( (hibyte2<hibyte1) and
                                                (lobyte2>lobyte1) ) );

The calculation of how many transfers done in both versions is:

                     nr_of_transfers := ( hibyte2 shl 8 + lobyte2 ) shr 1;

None of the above versions seem to give a stable result of the amount of
transfers done !!!
-----------------------------------------------------------------------
Mats strm             email:        mats.astrom@neurofys.uu.se
tel: +46 18 66 34 52                  Dept. of Clinical Neurophysiology
fax: +46 18 55 11 32                  University Hospital
                                      S-751 85 Uppsala
                                      Sweden
-----------------------------------------------------------------------

Re: DMA : numder of transfers

#692

Author: Jerzy Tarasiuk
Date: Mon, 05 Oct 1992 17:57

22 lines
1643 bytes

>>>>> On 1 Oct 1992 07:39:13 GMT, mats.astrom@neurofys.uu.se (Mats Astrom) said:
Mats> NNTP-Posting-Host: mats.neurofys.uu.se

Mats> While doing DMA-transfer it's possible to read the number of transfers done
Mats> by reading a specific register of the DMA-circuit. I've manage to do so but
Mats> the result seem to be somewhat instable ! The instability is due to reads of
Mats> the register in the middle of a transfer, isn't it ????
Mats> Assuming I'm setting up everthing correctly, how do I read the number of
Mats> transferred bytes to get the correct value every time ?????

Few questions:
1. did you remember to reset hi/lo flip-flop (I/O address 0Ch)
   before reading the DMA count register ?
2. do you remember the DMA count register contains remaining count,
   not count transferred and it goes down to -1 ?
3. why read registers many times (the repeat)? read once:
   port[DmaRstFF]:=0;
   l1:=port[DmaCntReg]; h1:=port[DmaCntReg];
   l2:=port[DmaCntReg]; h2:=port[DmaCntReg];
   IF h1<>h2 THEN cnt:=(h1 SHL 8)+l1 ELSE cnt:=(h2 SHL 8)+l2;
   Let me know if it gives stable results (i.e. still going down).
Jerzy Tarasiuk

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