Neil Russell awakens from a long day dream, and says:
We may have arived at a point that we cannot continue from. We have
four possible solutions to the peripheral controller problem. It should
be noted (if its not already obvious) that without the peripheral
controller the whole project is pointless.
1) Use a IDT 79R3730. This is the simplest and most attractive solution.
The 3730 provides all of the right things, with the possible exception
of video display support, which we have a solution for provided by
Steve Ligett. However, IDT are not forth comming on this part. I am
getting reluctance from the salesman at IDT in Santa Clara, and
Andy Busse has had similar problems trying to get information though
IDT in Germany. In fact, Andy has been told that if we want a design
now, don't use the 3730. Quite frankly, I don't have the confidence
in IDT to use it. So this option is out.
2) Use the MotherChip-set from Visual. Their chips will be available
in a few weeks, and for a good price. However, while they solve
the video problem quite nicely, there have no real support for
DMA, which makes SCSI and Ethernet difficult. As for providing
extra logic to suplement their short commings, it would be a
daunting task to do anything that would provide an efficient for
software solution. In fact, we may implement a good portion of
a peripheral controller in doing so, thus making the MOM chips
3) Use Ligett and Callen approach and do a DRAM controller in simple
logic and use another CPU (a 3041 in their case) to do the I/O
support. This would certainly provide the efficiency for
software that is needed, but the complexity and the fact that
a good DRAM controller is hard, especially for the 30x1, may make
this too complicated.
4) Implement a 3730 like thing in readily available logic. We could
use a load of PALs and various logic, or maybe one or two FPGA's.
Alternatively, we could have a semi-custom chip made. I'm told that
this may be cheap enough to consider. Prices for semi-custom are
based mostly on the pin count of the package used. I'm still
investigating this one, so I could be mis-informing you here.
5) Wait 6 months and begin again. By this time, the 3730 should be
out along with some possible R4000 solutions. I have heard that
R4200's may be available for as little as us$200 (quantity unknown).
However, we may well have the same peripheral controller problems.
While typing this, I had the thought that we could combine solutions
(2) and (3). So, the main CPU would have a MOM3000i (and maybe a
MOM3000d) and so would handle all the video. A single DMA interface
from the 3041 would be implemented with assistance from the MOM3000i.
All of the remaining peripherals are connected to the 3041 using its
bus sizing stuff. DMA is implemented using software loops in the 3041.
Some price guesses (for the peripheral and video sections):
MOM3000 chipset 50
EPROM 5 (8-bit wide)
SRAM (for the 3041) 20 (not necessarily 32-bit wide)
RAMDAC 30 (is this price right?)
We then add to that the prices that we have already established for
the SCSI, Ethernet, Serial, PCB, CPU, etc, and you have it.
As for the software in the 3041, it would be a seriously real-time
collection of interrupt driven loops, using registers and some SRAM
for buffering, with most of the data going directly to the main memory.
I do not see this would be a major problem.
Neil Russell (The wizard from OZ)
Pyramid Technology Email: firstname.lastname@example.org
3860 N. First Street Voice: (408) 428-7302
San Jose, CA 95134-1702 FAX: (408) 428-8845