🚀 go-pugleaf

A REAL PROJECT !!

I am attempting to design and build a video capture card for a PC.  I want
to transfer 8bit b&w video data from a standard ISA card directly to the
hard disk.  The data rate will be approx 500kbytes/s which I believe is the
maximum capability of most old IDE HDDs.  (I don't have the budget for a
fast IDE or SCSI)

I know that it is possible to setup a DMA transfer from a port to a chunk
of memory, but what I really need is to setup a transfer directly from a
port to disk.  Is this possible?  If I have to DMA from the port to memory,
and then out again to disk, I suspect that the system will not be fast
enough.

I have heard the rumour that standard IDE does not support DMA transfers.
This seems a little strange as the ATA interface does support DMA.  Where
does the inconsistency arise?  And what is the best way to transfer large
amounts of data, quickly to the HDD.

To give some background on the hardware, I plan to use dual port RAM on the
card to buffer the data.  Control electronics on the card would control the 
capture of the data, to one 'page' of ram, while the computer is pulling
data from the other 'page' of ram via DMA.  At the end of a frame, the
'pages' are swapped.  I plan to capture about 60 sec video data to a 40M
HDD file.  The specification disallows lossy compression, making MPEG a bit
of a non winner.  I could use compression, but that would probably need to
be implemented in hardware on the card.

I would like to dump the data to a standard file, but I could try just
dropping the data onto a particular chunk of disk.  (very carefully!)

If anyone is interested in following this project, email me and I will
start a distribution list, otherwise please comment.

Thanks, Andy.