Hi I've been thinking about this Atmega project which communicated with a DDR3 chip using GPIOs. I think I'm going to try this out with an FPGA. The data transfer rate will probably be terrible, but it seems to be an option.
Opinions?
Cheers -lev
On Sunday, July 18, 2021 8:51:41 PM WEST Hagen SANKOWSKI wrote:
Meeting Minutes of the Mumble session today
Participants: Devon, tatzelbrumm (partly), hsank, leviathan
Topics
- (external) RAM
While thinking about an RISC-V CPU demonstrator, we need memory for loading an Operating System like Linux.
Our first guess was for the demonstrator just to use external RAM chips, e.g. with HyperRAM, which has a quite simple interface and can be driven without LVDS-IO-Pads (which are still not available for us). Unfortunately using a couple of them gets fast quite expansive.
Using commercial available (and cheaper) DRAM nowadays is out of reach for us - this chips using a proprietary interface called DDR2 or DDR3. This interface needs differential IO-Pads (the LVDS we already mentioned above) and is critical about timing (in the meaning of different wire length, wire resistance and so on).
Without a PDK for a technology we can not design the analog stuff inside 'cause we still miss all the concrete values for the layers to calculate transistor and wire sizes.
- alternative: internal hand-crafted RAM-cells
Designing internal RAM cells, no matter whether dynamic RAM or static RAM isn't possible without the analog values from the PDK..
- possible pathes to go
- Reducing the Operating System to smaller memory footprints (e.g. with
NetBSD) and soldering a reasonable amount of HyperRAM close to the CPU
- Getting a PDK and design with a couple of iterations in silicon our
analog stuff (LVDS-IO-Pads or RAM-cells hand-crafted) 'till it works..
'''' Note: if we'd start with an alien PDK we had to re-design the analog stuff from ground up again for our LibreSilicon PDK again.. ''''
If you have some suggestions how to get out of our chicken-and-egg-Problem, please drop us an email :-)
Regards, Hagen _______________________________________________ Libresilicon-developers mailing list Libresilicon-developers@list.libresilicon.com https://list.libresilicon.com/mailman/listinfo/libresilicon-developers