Questions tagged [dma]
Direct Memory Access in historical computers and the history of DMA itself. DMA allows peripherals to access memory directly without using the main processor.
12 questions
6 votes
0 answers
221 views
Did any notable 6502 systems coordinate DMA with start of instruction rather than adding delay for possible writes?
An annoying hardware quirk of the 6502 is that while the READY line can be used to extend read operations, it cannot be used likewise for writes. As a result, systems which need to accommodate DMA ...
- 41.2k
8 votes
1 answer
332 views
Does MSX support DMA from slots?
I was looking at the signals present on the slot connector of an MSX machine, but can't find any valid option to implement DMA. So, no such an option on these systems?
- 469
8 votes
1 answer
1k views
How does the VIC-II/CPU memory access work on the C64?
As a programmer I knew that on the C64 the CPU got the bus in the high phase of PHI2 and the VIC-II got it in the low phase and also stole extra high phases when required. However, it wasn't until ...
- 263
2 votes
0 answers
254 views
Apple II DMA daisy chain also used to arbitrate /INH?
On the Apple II series of computers, peripheral cards contend for bus mastership through a priority daisy-chain system. A peripheral card is only allowed to perform DMA if its DMA_IN line is at logic ...
- 915
13 votes
3 answers
2k views
PC/AT two DMA controllers - what is the purpose of cascade channel and how did it work?
Why did the design need to reserve one channel for cascade, how did it work and what exactly was going on there?
- 2,893
12 votes
1 answer
2k views
What is the exact bus protocol used by the C64/C128 REU?
The Commodore 64/128 RAM Expansion Units used a DMA controller to move data between the REU's RAM and system RAM (or I/O space). One would set the addreses, length and direction for the transfer (or ...
- 29.5k