Subject: Re: [BBC-Micro] 32016 + 32082
From: [email-masked]
To: <[email-masked]>
Date: Thu, 15 Dec 2011 02:00:36 +0000
List-Id: BBC Micro & related machines <bbc-micro.lists.cloud9.co.uk>

Eelco Huininga wrote:
> This might suggest that they explored the use of a MMU during the
> development of Pandora v0.61 but abandonded it by the time Pandora 
> v2.00
> was developed, or that they moved MMU functionality from the firmware 
> to
> software.

It could be they changed the programming assumption that if you were
running on Pandora 2.00+ it was up to running software to decide
whether there was MMU present or not.

Indeed, on startup Pandora 2.00 explicity sets the local copy of the
config settings to &01, so calls to OS_CONFIG return "no MMU present".

029A DC D0 31    ÜÐ1  MOVQB  +1,&31(SB)   ; FPU=1, MMU=0

; SVC &36 - Read config switches
090E CE 58 D0 31 ÎXÐ1 MOVZBD &31(SB),R1   ; Get byte from workspace
0912 EA BD D8    ê½Ø  BAL &000046EA       ; Jump to exit

...and on startup configures the hardware to not use an MMU:

0000 0E 0B 01    ...  SETCFGD +2            ; Configure FPU present, 
IRQ, MMU, CSLV absent
0003 7F AA C0 F0 01 7E
                  .ªÀð.~ JUMPD @&00F0017E    ; Jump to startup code

suggesting it's up to running software to chose to detect, enable and
use any MMU.

Interestingly, there is something in the OSFILE code that reads the
config switches from hardware, &0AFC onwards. I haven't investigated
enough to work out what's going on there.

http://mdfs.net/Software/Tube/32016/v200/Pandora.lst

JGH

_______________________________________________
bbc-micro mailing list
[email-masked]
http://lists.cloud9.co.uk/mailman/listinfo/bbc-micro