[openMSX-devel] [ openmsx-Feature Requests-1305071 ] ADVRAM support

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Feature Requests item #1305071, was opened at 2005-09-26 20:17
Message generated for change (Comment added) made by arnoldmnl
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Category: MSX devices support
Group: None
Status: Open
Priority: 1
Submitted By: Arnold Metselaar (arnoldmnl)
Assigned to: Nobody/Anonymous (nobody)
Summary: ADVRAM support

Initial Comment:
Grupo MSX projetos has made an extension called ADVRAM
that allows the CPU to directly access the VRAM, see
http://www.carchano.com.br/portal/msxprojetos.asp ->
advram. 

For those with limited understanding of Portugese:

* The video ram appears as a memory mapper in page 2 of
slot 0, both reading and writing are supported. 
* Selecting a 16 KiB block from the Vram is done with
with the standard mapper register on port 0xFE. 
* LD A,1 followed by IN A,(9AH) sets interleaved mode
as used in screen 7 and higher.
* LD A,0 followed by IN A,(9AH) sets normal mode as
used in screen 6 and lower.

It would be nice to support this in openMSX

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>Comment By: Arnold Metselaar (arnoldmnl)
Date: 2005-12-04 22:04

Message:
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ADVram is now implemented with a change in the layout of the
control register:
ld a, xx 
in a,(9Ah)
; xx=0 -> disabled
; xx=80h -> linear mode; 
; xx=0C0h -> planar mode
Reading port 9Ah on a Turbo R may or may not trigger the vdp
io delay, if it does the VDPIODelayDevice will need to
accomodate for two dependent devices.
The attached file measures the time needed for 256*32 times
in l,(c). Usage: delay 40 98 9a 

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