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;Set (fudge) VDU Workspace values
;________________________________________________________________
.VduWorkspace
lda #5 ; Record screen mode . We're actually setting up a custom 8k screen mode - but it's based on mode 5.
      ; We do this so the VDU 19 OS routines called below set the palette correctly.
sta &355 ; The OS refers to this mem location in VDU routines. See p277 AUG.

lda #3 ; Record number of logical colours minus one.
      ; We do this so the VDU 19 OS routines called below set the palette correctly.
sta &360 ; The OS refers to this mem location in VDU routines. See p277 AUG

lda #16 ; Record 16 bytes per character.
      ; We do this so the VDU 19 OS routines called below set the palette correctly.
sta &34f ; The OS refers to this mem location in VDU routines. See p276 AUG
;________________________________________________________________

<snip>
;VDU 19 calls
;________________________________________________________________
;We need to set the logical colours ourselves,
;even if we wanted the defaults for a 4 colour screen.
;This is because we have set our own screen mode without
;calling the normal OS routines which would initialise everything
;like colour defaults for us.

.vdu19
;Logical col 0 = blue
lda #&0c       ; OSWORD call for VDU 19
LDX #c0 MOD 256 ; param
LDY #c0 DIV 256    ; block
jsr osword

.
.
.
<snip>

Author:	jbnbeeb [ Mon Jun 09, 2014 6:07 pm ]
Post subject:	Changing to a custom screen mode
Hi, I first asked about this at the bottom of a previous thread.. but it was kind of a thread derail.. and I'm still stuck on this problem http://www.retrosoftware.co.uk/forum/viewtopic.php?f=73&t=881 My objective: to change from a regular screen mode -- such as Mode 7 - to a custom 8k screen mode (which is a 128x256 pixel screen based on Mode 5). I want to be able to do this without wiping the memory between &5800 and &6000. What is working: I can get an "8k MODE 5" by first changing to MODE 5 and then setting values in CRTC for 128x256 pixel screen and the screen start addr to &6000 What isn't working: By changing to Mode 5 first, I wipe the memory between 5800-6000. To try to resolve this, starting from Mode 7, I do the following: a) clearing screen by writing zeroes to 6000-8000 b) setting all CRTC values to reflect an 8k mode 5 (ie keep the params to those in the Advanced User Guide for Mode 5 except chars per line and screen address) c) Set the video ula &FE20 to &C4 (ie Mode 5) d) Set the palette register to default mode 5 values by issuing VDU 20 (lda #20;jsr oswrch) e) Set addressable latch for 8k screen: ldx #4+8 : stx SysViaRegB \\ these two set the ldx #5+0 : stx SysViaRegB \\ screen size to 8k RESULT: the screen clears, but when plotting pixels, I get distorted results - essentially fragments of MODE 7 text characters in the area where pixels should be plotted..within an 8k screen area.. ie 32x32 char screen. Where am I going wrong? Is what I'm aiming for possible?

Author:	TomW [ Mon Jun 09, 2014 8:51 pm ]
Post subject:	Re: Changing to a custom screen mode
Sound like the OS is re-programming the video ULA behind your back. Either use OSBYTE &9a to change the ULA control register, write to the shadow copy at &248 as well as &fe20, or disable interrupts and bin the OS.

Author:	jbnbeeb [ Tue Jun 10, 2014 6:07 pm ]
Post subject:	Re: Changing to a custom screen mode
Thanks Tom. Looks like that is what was happening. I used OSBYTE &9A which did the trick, mostly. I then got a blank white screen. Issuing VDU 19 OSWORD calls to change the palette didn't work properly. I realised this was because VDU workspace wasn't being initialised to what I needed - i.e values suitable for MODE 5, which is pretty much what the 8k mode I'm using is, albeit 128x256 pixels. So I took a look at the memory layout notes in the AUG and fudged a few values so that the VDU 19 OSWORD calls worked correctly. Code snippet below for those who might be interested Code: ;Set (fudge) VDU Workspace values ;________________________________________________________________ .VduWorkspace lda #5 ; Record screen mode . We're actually setting up a custom 8k screen mode - but it's based on mode 5. ; We do this so the VDU 19 OS routines called below set the palette correctly. sta &355 ; The OS refers to this mem location in VDU routines. See p277 AUG. lda #3 ; Record number of logical colours minus one. ; We do this so the VDU 19 OS routines called below set the palette correctly. sta &360 ; The OS refers to this mem location in VDU routines. See p277 AUG lda #16 ; Record 16 bytes per character. ; We do this so the VDU 19 OS routines called below set the palette correctly. sta &34f ; The OS refers to this mem location in VDU routines. See p276 AUG ;________________________________________________________________ <snip> ;VDU 19 calls ;________________________________________________________________ ;We need to set the logical colours ourselves, ;even if we wanted the defaults for a 4 colour screen. ;This is because we have set our own screen mode without ;calling the normal OS routines which would initialise everything ;like colour defaults for us. .vdu19 ;Logical col 0 = blue lda #&0c ; OSWORD call for VDU 19 LDX #c0 MOD 256 ; param LDY #c0 DIV 256 ; block jsr osword . . . <snip> TomW wrote: Sound like the OS is re-programming the video ULA behind your back. Either use OSBYTE &9a to change the ULA control register, write to the shadow copy at &248 as well as &fe20, or disable interrupts and bin the OS.

Author:	tricky [ Tue Jun 10, 2014 10:25 pm ]
Post subject:	Re: Changing to a custom screen mode
Glad you got it sorted, I can "go straight to the metal", but have only learned one OSBYTE call (1 - or is it 0)!

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