Date   : Thu, 11 Nov 2004 10:18:58 +0000
From   : Richard_Talbot-Watkins@...
Subject: Re: SRAM

Andrew W wrote on 11/11/2004 00:58:50:

> I've been trying some SRAM routines from an old Beebug magazine. The
> poke and 'pick' routines both use OSWORD 66. I'm trying these under
> emulation so I'm not quite sure what is implemented. Could anybody
> say what is this routine and where is it stored?

The sideways RAM utilities live in the 1770 DFS ROM on the B+/128 and
Master.

Four new commands are provided (here is their implementation on the B+128):

OSWORD 66
Block Transfer

The parameter block:=AD

XY+ 0     bit 7 clear/set for READ/WRITE
          bit 6 clear/set for ABSOLUTE/PSEUDO
    1=AD4   Main RAM address
    5=AD6   Block Length
    7     ROM ID 0=ADF
    8=AD9   SRAM address


OSWORD 67
Load/Save

The parameter block:=AD

XY+ 0     bit 7 clear/set for SAVE/LOAD
          bit 6 clear/set for ABSOLUTE/CONTIGUOUS
    1=AD2   File Name address
    3     ROM ID 0-F
    4=AD5   File length
    6=AD7   Buffer Start address
    8=AD9   Buffer length, 0 for default,
             >=32K for buffer from OSHWM to bottom of screen memory


OSBYTE 68
Test RAM Presence

Returns a byte in X

  7             0
  * =AD F E 1 0 D C     RAM Present flags

* =AD bit 7 set if E/F are being used for 3rd and 4th pages.
Bits 0=AD5 set if RAM pages found in given slot on last BREAK/POWER ON.


OSBYTE 69
Test Pseudo/Absolute Use of Page

Returns a byte in X.

Bit 7    as for OSBYTE 68,
Bits 0=AD5 set if RAM in given slot (see above) is
         being used in PSEUDO addressing mode.


The "pseudo" addressing mode refers to the way in which four SRAM banks can
be considered as one contiguous block of memory indexed from addresses 0 to
65472.  This can be handy for using sideways RAM as a simple RAM disc for
temporary data storage.  The banks to use as pseudo-addressed need to be
specified by *SRDATA W|X|Y|Z... I don't know if there is an OSWORD/OSBYTE
way of doing this though.

More about this here:

http://acorn.riscos.com/documents/appnotes/016-030/030.ps

Rich



**********************************************************************
This email and any files transmitted with it are confidential and
intended solely for the use of the individual or entity to whom they
are addressed. If you have received this email in error please notify
postmaster@...

This footnote also confirms that this email message has been checked
for all known viruses.

**********************************************************************
Sony Computer Entertainment Europe