23 Dec
2013
23 Dec
'13
8:22 a.m.
On Fri, Dec 20, 2013 at 12:05:34PM -0500, Ethan Dicks wrote:
[...] I naturally wondered what it would take to adapt
the Zorro Bus (or the
86-pin SOTS bus on the A1000, really) to the Unibus so I could use an RL11 on
it. We had all the necessary components for a simple Amiga-Unibus adapter,
but the Amiga doesn't have a DMA controller, [...]
That's because it didn't need one. Zorro I was little more than the CPU lines
being exposed on an edge connector. So you could tri-state the CPU and then
access memory directly without needing to jump through the hoops of a DMA
controller.
Your hardware effectively *is* the CPU for the duration, and there was at least
one CPU accelerator that exploited this ability, and didn't need one to void
the warranty by cracking open the case and pulling out the 68000 like some
accelerators.
(It would perhaps be entertaining to build one such accelerator that contains
a modern CPU running a 68k emulator.)