[Oberon] Oberon on ULX3S explanation

[Paul Reed]

Hi Lyall,

> In my understanding, a typical PC uses DRAM.  Kernel.Mod has several
> CONSTs defined under (* memory management *).  Is memory operation in
> S3, Native Oberon, useful as an example?

Sadly not, except in the very broadest sense.  In a PC, the hardware is 
designed by the manufacturers and the software can use it because it 
conforms to a de-facto standard arrangement.  We don't get to change it. 
  With an FPGA board, we design the hardware ourselves - hopefully 
enabling an understanding of how things work at this level.

Unfortunately, although commonly-used because it's cheap per bit, 
synchronous DRAM is much more complicated than the fast asynchronous 
static RAM used in the Oberon FPGA reference design.  Getting a 
description of how this was implemented on the ULX3S board would have 
been useful in understanding the design trade-offs, but unfortunately 
all we got was another advert.

Rowhammer (https://en.wikipedia.org/wiki/Row_hammer) is an example of a 
security exploit in PCs which takes advantage of the complexity of the 
PC's SDRAM implementation.

HTH,
Paul