Re: [hatari-devel] test needed on a 4MB STF

[ Thread Index | Date Index | More Archives ]

Christian Zietz schrieb:

> I think this can be fully explained by the mapping that I posted earlier
> and that you then confirmed for the non-IMP MMU -- which is made by
> Ricoh, BTW.

To further support my last post, I repeated the test you described on my
4 MiB STF with Ricoh MMU. So, bank 0 is set to 128k, the address is set
to $20000. This ends up on bank 1 as: offset $80000 (bank 1 = 128k),
offset $40000 (bank 1 = 512k), offset $20000 (bank 1 = 2M). You can see
how A17 is mapped to CAS8, CAS7 and CAS6, respectively. In case of a
bank that in reality has 2 MiB, this corresponds to offsets $80000,
$40000 and $20000 -- the same I observed.

Then I did the test with bank 0 set to 512k and the address set to
$80000, i.e. A19=1. This accesses bank 1 as: offset 0 (bank 1 = 128k),
offset $100000 (bank 1 = 512k) and offset $80000 (bank 1 = 2M). This is
again consistent with my explanation: In the case of a 128k setting for
bank 1, A19 is simply not considered. For the 512k setting it maps to
CAS9, which explains the observed offset $100000. For the 2M setting A19
maps to CAS8, i.e. offset $80000.

I think it shouldn't be to hard to express that behaviour in code.

Christian Zietz  -  CHZ-Soft  -  czietz@xxxxxxx
PGP/GnuPG-Key-ID: 0x52CB97F66DA025CA / 0x6DA025CA

Mail converted by MHonArc 2.6.19+