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Re: ECB-DMA [message #6782 is a reply to message #6780]

Sat, 16 November 2019 05:23

etchedpixels
Messages: 333
Registered: October 2015

Senior Member

Take a look at Marten's Z80DMA for RC2014. It's a much simpler bus so rather easier to understand IMHO.

IEI/IEO was always a problem with backplanes. S100 systems generally don't use it - S100 after all has its own set of vectored interrupts. Cromemco systems did but they use flying leads for it so that you can chain interrupts neatly without having to worry about exact slot orders and magic jumpers in unused slots. The 16x50 on the board doesn't support IEI/IEO anyway so you can't really use Z80 IM2 properly. What you can do though is to use the spare modem pins on the 16x50 as an interrupt controller as it will let you generate interrupts on modem line changes. That (plus a 10Hz clock board) is how I run Fuzix on SBCv2.

S100 also solved the DMA access problems its own unique way and supports priority bus mastering so is a whole chunk of extra logic you probably wouldn't want to copy.

The Z80DMA isn't actually much use for bank to bank copying unless you've got a better MMU design. On a Zeta v2 style MMU you can map any pair of 16K banks and DMA between them. On the SBCv2 you'd need to have some kind of separate DMA bank select logic and latches - like the Altos 5 did. CP/M 3 bank to bank copying is not usually much of a win anyway. It gets you a slightly bigger TPA but at a measurable performance hit over not having XMOVE and ending up with a 512 byte buffer per CF drive (drive in CP/M sense) in the common.

CP/M 2.2 it's hard to use the Z80DMA effectively. CP/M 3 for I/O you can at least do larger I/O directly using the DMA (in particular the CCP loading applications which is one of the most obvious 'feels fast' points) but not really use it for buffering, for MP/M it fits much better as MP/M expects your driver transfer code to be in common space and you switch bank to the target, do the I/O then switch back. That plus the fact you know about multi-block I/O fits the DMA better.

For floppy the biggest use IMHO is that you can leave interrupts on during transfers even on 1.44/2.88MB media and you'll not drop anything. Very useful in MP/M.

I'm wary of just blindly going to a raw CF adapter. The number of incompatibilities and timing issues with that is proving inconveniently large in other projects.

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[Message index]

		ECB-DMA By: b1ackmai1er on Sun, 10 November 2019 00:16
		Re: ECB-DMA By: Wayne W on Tue, 12 November 2019 12:31
		Re: ECB-DMA By: jcoffman on Tue, 12 November 2019 16:14
		Re: ECB-DMA By: etchedpixels on Wed, 13 November 2019 15:40
		Re: ECB-DMA By: b1ackmai1er on Fri, 15 November 2019 20:34
		Re: ECB-DMA By: b1ackmai1er on Sat, 16 November 2019 04:56
		Re: ECB-DMA By: etchedpixels on Sat, 16 November 2019 05:23
		Re: ECB-DMA By: jcoffman on Sat, 16 November 2019 08:03
		Re: ECB-DMA By: wsm on Sat, 16 November 2019 09:28
		Re: ECB-DMA By: jcoffman on Sat, 16 November 2019 13:09
		Re: ECB-DMA By: wsm on Sat, 16 November 2019 14:02
		Re: ECB-DMA By: b1ackmai1er on Sun, 17 November 2019 05:50
		Re: ECB-DMA By: jcoffman on Sun, 17 November 2019 07:06
		Re: ECB-DMA By: etchedpixels on Sun, 17 November 2019 07:41
		Re: ECB-DMA By: wsm on Sun, 17 November 2019 10:06
		Re: ECB-DMA By: wsm on Sun, 17 November 2019 14:12
		Re: ECB-DMA By: jcoffman on Sun, 17 November 2019 21:28
		Re: ECB-DMA By: rcini on Thu, 12 December 2019 17:52
		Re: ECB-DMA By: wsm on Thu, 12 December 2019 21:24
		Re: ECB-DMA By: rcini on Fri, 13 December 2019 07:22
		Re: ECB-DMA By: mikesmith on Thu, 09 January 2020 18:36
		Re: ECB-DMA By: wsm on Thu, 09 January 2020 20:28
		Re: ECB-DMA By: lynchaj on Mon, 26 April 2021 09:03
		Re: ECB-DMA By: lynchaj on Tue, 27 April 2021 04:41
		Re: ECB-DMA By: lynchaj on Wed, 28 April 2021 08:00
		Re: ECB-DMA By: jcoffman on Sat, 16 November 2019 07:56
		Re: ECB-DMA By: jcoffman on Sat, 16 November 2019 07:45
		Re: ECB-DMA By: b1ackmai1er on Thu, 17 June 2021 07:14
		Re: ECB-DMA By: lynchaj on Thu, 17 June 2021 07:29
		Re: ECB-DMA By: b1ackmai1er on Sat, 19 June 2021 05:33
		Re: ECB-DMA By: lynchaj on Sat, 19 June 2021 07:11
		Re: ECB-DMA By: lynchaj on Sat, 19 June 2021 07:30
		Re: ECB-DMA By: b1ackmai1er on Mon, 21 June 2021 07:31
		Re: ECB-DMA By: b1ackmai1er on Sat, 26 June 2021 19:10
		Re: ECB-DMA By: b1ackmai1er on Fri, 02 July 2021 02:06
		Re: ECB-DMA By: lynchaj on Fri, 02 July 2021 04:49
		Re: ECB-DMA By: b1ackmai1er on Fri, 02 July 2021 07:23
		Re: ECB-DMA By: etchedpixels on Thu, 08 July 2021 08:22
		Re: ECB-DMA By: b1ackmai1er on Fri, 09 July 2021 22:08
		Re: ECB-DMA By: lynchaj on Tue, 13 July 2021 11:44
		Re: ECB-DMA By: lynchaj on Thu, 29 July 2021 12:15
		Re: ECB-DMA By: b1ackmai1er on Sun, 04 July 2021 08:09
		Re: ECB-DMA By: b1ackmai1er on Mon, 05 July 2021 07:35
		Re: ECB-DMA By: lynchaj on Wed, 07 July 2021 03:27
		Re: ECB-DMA By: lynchaj on Wed, 07 July 2021 03:44
		Re: ECB-DMA By: lynchaj on Mon, 14 March 2022 03:48
		Re: ECB-DMA By: lynchaj on Wed, 23 March 2022 10:05

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