[Oberon] SDRAM performance

[D EMARD]

Hyperram is nice but take into consideration that
only cypress makes them Mouser has them on stock
and should be ok for now.

On ULX3S the only vendor-specific
part was FPGA and last months we have problems getting
the parts but we managed,

low-cost grades 6 are hardly available, hackaday
for their conference badges had to buy expensive grade 8 to
meet deadlines :)


On 11/15/19, Skulski, Wojciech <skulski at pas.rochester.edu> wrote:
> Joerg:
>> So all in all: 70 ns seems reasonable for random access. Consecutive burst
>> reads are MUCH faster.
>
> Looking at this discussion and other information sources, I now think that
> either Cellular RAM or HyperRAM will be the most reasonable choices for
> future FPGA designs which require substantial memory space. These
> technologies are less suitable for hard silicon CPUs unless the controllers
> are integrated into ASICs before hand. In case of the FPGAs the controllers
> can be retrofitted and/or swapped after the boards are designed.
>
> The best number reported for the HyperRAM is WR/RD = 66/102 ns at CLK = 166
> MHz and 1x Latency settings of the chip and the controller. It is on par
> with SDRAM at much lower implementation hassle. These numbers are claimed by
> the controller #1 below.
>
> Two HyperRAM controllers which I found thus far:
>
> 1) Portable Verilog RTL interface to S27KL0641DABHI020 64Mbit HyperRAM. Very
> well documented.
>    https://github.com/blackmesalabs/hyperram
>
> 2) A basic HyperRAM controller for Lattice iCE40 Ultraplus FPGAs
>   Full source and very simple. Poorly documented (i.e., undocumented on par
> with the spirit of Oberon).
>
> 3) A full AXI bus controller design is also available from Cypress. It is
> very professionally done with full reports, specs, and everything. It is
> clearly a great design for great professionals. Not me!
>
> The Cellular RAM video application note with very reasonable documentation
> for the Digilent Nexys-3 board:
>
> 3) https://my.eng.utah.edu/~kalla/index_3710.html
>   Scroll to the lines titled "If you want to use the Cellular RAM, Paymon
> found the following materials". The files are linked right below that line.
>
> Hope it helps.
>
> W.
>
>
>
>
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