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Old 16 May 2020, 03:06   #1
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16 bit DMAC example for DIY Zorro cards

I've been looking around to try and figure out how to interface to the Zorro bus with DMA.-

Looking at the 2091 design shows that the 8 bit SCSI chip is linked through the DMAC chip which supplies 16bits to the onboard FAST RAM expansion but then has only an 8 bit bus to the 8 bit SCSI chip. There are not an extra 8 bits to use for a 16 bit chip.

So i thought about looking at the 4091, but the schematics don't seem to be available.

GVP EGS Spectrum uses a Mach 210 CPLD to convert Zorro to the 16 bit ISA bus interfaced Cirrus Logic GD5426. So that code might be the 16 bit DMAC example that i want...

Picasso II is basically the same card as the GVP Spectrum, using Cirrus Logic GD5426, so its PALs probably have similar code to the MACH 210 CPLD on the GVP card.

Picasso IV has a PCI Graphics processor and the signal is converted to Zorro through an old FPGA from Xilinx named XC5210. Its been programmed with software which can no longer function as it requires registration the Xilinx server that was discontinued in 2008. So the software would need to be cracked.
But if you were to get working software, you would then be struck that it was created with a high level language CanDo type program which does not generate any kind of linear programmable source code, only FPGA bit stream. So it cannot be read and converted anyway.

So this leaves the GVP MACH210 code as the best prospect as a "Lego block" piece for easier development like they use in the PC industry (PCI, PCIe, USB).

Principally I'm wanting to connect a 16 bit SCSI chip, the 53c720 which sits between the A4000T (53c710) and the CyberStorm (53c770) models.

Are there any easy 16 bit examples to follow, like the 4091 design schematics?
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Old 16 May 2020, 10:48   #2
Toni Wilen
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AFAIK none of Amiga display cards use DMA.

Some SVGA chips do support blitter DMA to/from (PC) system memory but it is not DMA from Amiga side (not even PicassoIV), blitter DMA operation is started normally but then Amiga side driver simply writes repeatedly to same 16-bit IO port register. (Like PIO IDE).

(and isn't 53C710 and later chips all 32-bit and have built-in 32-bit DMA engine?)
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Old 16 May 2020, 12:36   #3
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Yes good point about the chips! They only have a 16 bit SCSI bus, but their CPU bus is 32 bits.
Perhaps a new Video card could benefit from having DMA on board?

I wonder if the Prometheus has DMA over the Zorro bus?
Memory region
Within this region, only memory read / write commands are posted.
The memory region is 508MB sized and can be addressed linearly without any
banking mechanisms.
Please note: the DMA buffer memory (aka the gfx card) should be located into
the lowest 16MB region of this block. Many PCI sound cards can only do 24bit
DMA and only access this 16MB block.
Look like it doesn't contain DMA for Zorro, but maybe a PCI chips own DMA may work over the Zorro bus.

The Picasso IV used a Cirrus Logic GD5446. I'll have to look again at the manual and see if anything about DMA is mentioned. It uses a PCI bus, so maybe a Zorro3 version using Prometheus could give DMA over Zorro?

If so then this could also work for 800 series PCI type SCSI chips.
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Old 16 May 2020, 16:59   #4
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Apparently the CBM A2410 TIGA graphics card has DMA support
It has a Texas Instruments TMS34010 chip, with 16bit transfer.
It does however mention in the Amiga DevCon Denver 1991 document

DMA Functions: The DMA function does not give a performance improvement on 68030 system. Only use the function on 68000
EDIT: Heres a link to the user guide for the TMS34010 interesting as its designed for use with either 8086/68000 endian modes

I was reading somewhere that DMA is either card based or CPU, Im guessing that card based, you are replacing the CPU temporarily and handling the transfer to RAM yourself with your own `processor`
But please ignore that assumption if Im completely wrong however!

Last edited by Juz400; 22 May 2020 at 14:30. Reason: Link for User guide
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Old 16 May 2020, 17:20   #5
Toni Wilen
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Problem with Z2 DMA boards is that they only have 24-bit addressing capability but most 68030+ boards have Fast RAM outside of 24-bit address space: DMA to/from Fast RAM is not possibly without first CPU copying it to/from chip ram first and then using DMA. Which is slower than using CPU only.
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Old 17 May 2020, 15:16   #6
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How about the A4000T SCSI? This is not exactly a Zorro-3 device but it is DMA and is very similar to the A4091.
The A4091 GALs shouldn't be protected so they should be readable, though that doesn't give you the source.

Nevermind, they are right here with source and comments:
From Dave Haynie's archives, lots of good stuff there. The BigRAM is basically a Z3 memory card, not DMA but should have a bit to get you started.

I recall Michael Boehmer had some good Zorro 3 documentation as well. Might be just remembering the Deneb FAQ which has some general Z3/DMA questions.

If you're looking for a Z2/Z3 RTG GFX design, there's Matze's GBAPII++ which is all open.

Last edited by grelbfarlk; 18 May 2020 at 05:45.
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