Re: RR/MMC64/uIEC/REU All in one idea.
- From: "Nathan Beckstrand" <nathan.beck@xxxxxxxxx>
- Date: 16 Nov 2005 22:17:14 -0800
Ok, here are some parts I am looking at:
AT94K05AL FPSLIC
http://www.atmel.com/dyn/products/devices.asp?family_id=627
This is 25Mhz AVR with 5K gate FPGA and 36KB of on chip SRAM. You won't
be making a SuperCPU with this but I think it would make a fine DMA
engine. It can be had for as little as $13.15 from Digikey. This device
has no flash or EEPROM so that will need to be a separate chip. The
flash chip needs only to hold a small program that allows the AVR to
load a boot file from the SD/MMC card. The rest of the device
configuration will be done with the file loaded from SD/MMC.
Ok, SD/MMC cards are fast. Are they fast enough to eliminate the need
for the SRAM chip? I think so. The REU can just as easily be a virtual
REU located on the SD/MMC card. But will this wear out your SD/MMC
card? Probably not for a very long time. The other problem is the SRAM
was going to hold the cartridge ROM. This only needs to be max 8KB, so
the AT94K05AL SRAM can easily handle that. But what about different
cartridge ROM banks? Easy, just hold the DMA line (to stop the cpu)
while you swap it in from the SD/MMC card. So, if we don't really need
a stand alone SDRAM chip, we can save a lot of complexity. Where do we
put the FAT table though?
The reset button is the freeze button! The reset switch is not
connected to the reset line, it is connected to an I/O line on the
AT94K05AL. When you press the reset button, the AT94K05AL saves the C64
RAM and state to a file on the SD/MMC. It then performs a normal reset.
When the system comes back up it presents you with a choice to
permanently save the freeze file or simply discard it. This behavior is
fully configurable in the BIOS settings area.
No more clock port. Instead I want to put a LAN port and serial port
directly on the cartridge. Why not kill a couple more birds with this
stone? The serial port will just be a level converter from the FPGA.
The LAN will be NC28J60:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en022889
This chip is small, low pin count and uses a simple serial interface.
I would really like some way to copy files from one SD/MMC to another.
Option A: Put a second SD/MMC connector on the cartridge, but where?
Option B: Use a bigger serial flash chip as a buffer.
Option C: Bring back the SRAM and use it as a buffer.
Maybe a serial SRAM? Or, does anyone know if there exists a SDRAM with
a simple serial interface and low pin count. This would be a SDRAM with
controller on the chip. That would be awesome, you could easily have a
multi megabyte RAM with one of those.
Most important of all, this project must fit inside a Retro Replay
cartridge.
Connectors:
SD/MMC (one or two.)
9 pin DIN serial port.
RJ45 LAN.
IEC header.
Reset/freeze switch.
Flash write protect switch.
Watch battery holder.
IC/Electronics:
AVR/FPGA chip.
Serial flash chip.
LAN chip.
LAN level converter chip.
Serial level converter chip.
3.3v regulator.
25Mhz crystal.
32.768Khz clock crystal.
4 caps for crystal.
LEDs for WAN(2), SD/MMC activity.
Several resistors.
God knows what else...
As you can see, this has been turning in my head non stop.
.
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- From: Nathan Beckstrand
- Re: RR/MMC64/uIEC/REU All in one idea.
- From: Jim Brain
- RR/MMC64/uIEC/REU All in one idea.
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