[Oberon] [EXT] Re: Project Oberon on Arty A7

Skulski, Wojciech skulski at pas.rochester.edu
Wed Dec 9 19:46:19 CET 2020


>I did consider using an SPI RAM shield but didn't think long about it as I assumed the SPI interface would be too slow.

Yes, they are discouragingly slow. No way to run the bit mapped video. But Astrobe is not using any such. You demonstrated SPI video. I have not looked into it, but I presume it does not need much speed.

The SPI RAM opens the door to truly small controller boards running Astrobe at low clock speed. The CPU can be either RISC5 in a small FPGA or one of the ARMs which you support, or an entirely new very small ARM. I do realize that making boards is an entirely separate domain. A low volume production must lose money, unless it is a part of a larger project. We discussed it at length. But it may be worth keeping in mind if there is an opportunity.

> I haven't yet managed to find any Arduino / ChipKit - compatible boards that use SRAM directly. However, you have triggered another idea. I have one of Magnus Karlsson's / Saanlima Electronics Oberon 'wings' (2xPS/2 and 1 Mbyte of SRAM)

Looking at the Arty-7 schematics of the Arduino/ChipKit I can see 32 pins on page 3. Then I looked at the ASRAM chips. The 256kB (16 bit interface) chip IS61LV25616AL needs A0 to A17, D0 to D15, and control pins WE#, OE#, CE#. Too many pins. 

The 1Mx8 chip (8 bit interface) IS61WV10248BLL-10TI needs A0 to A19, D0 to D7, and control pins WE#, OE#, CE#. Total 20+8+3 = 31 pins. So there is a chance to develop such a shield, if it is not available from Saanlima.

Note that Cmod A7 has such a chip on board. So you can look at developing the memory controller for it using Cmod A7. It is still ASRAM, which you need to access four times to deal with 32 bits.


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