Z80:Application Variables (AppVars) - Revision history

KermMartian at 07:59, 6 February 2016

2016-02-06T07:59:15Z

← Older revision		Revision as of 07:59, 6 February 2016
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	=== Creation ===		=== Creation ===

	Creating an identifier is as simple as [[Z80:Opcodes:~~ldir~~\|ldir-ing]] into the AppVar.		Creating an identifier is as simple as [[Z80:Opcodes:LDIR\|ldir-ing]] into the AppVar.

	;load our identifier		;load our identifier

KermMartian: /* Detection */ Correction from current z80 Heaven

2016-02-05T01:58:17Z

Detection: Correction from current z80 Heaven

← Older revision		Revision as of 01:58, 5 February 2016
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	ld hl,identifier		ld hl,identifier
	ex hl~~,de~~		ex de,hl
	iloop:		iloop:
	ld a,(de)		ld a,(de)
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	identifier:		identifier:
	.db "identify",0		.db "identify",0


	= Changing AppVar Size =		= Changing AppVar Size =

KermMartian: Adjusted lowercase z80

2016-02-03T21:08:52Z

Adjusted lowercase z80

← Older revision		Revision as of 21:08, 3 February 2016
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	In the [[~~z80~~:Application Code\|last tutorial]] we pointed out that you can not create permanent self modifying code. So, how do you save important data? The answer is in AppVars. They are a special kind of variable that can only be edited in assembly, and serve as a "permanent" saving point for app data (note that they can be deleted from the memory menu).		In the [[Z80:Application Code\|last tutorial]] we pointed out that you can not create permanent self modifying code. So, how do you save important data? The answer is in AppVars. They are a special kind of variable that can only be edited in assembly, and serve as a "permanent" saving point for app data (note that they can be deleted from the memory menu).

	= Creating AppVars =		= Creating AppVars =
Line 26:		Line 26:
	=== Creation ===		=== Creation ===

	Creating an identifier is as simple as [[~~z80~~:Opcodes:ldir\|ldir-ing]] into the AppVar.		Creating an identifier is as simple as [[Z80:Opcodes:ldir\|ldir-ing]] into the AppVar.

	;load our identifier		;load our identifier
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	{{lowercase}}		{{lowercase}}
	[[Category:~~z80~~ Assembly]]		[[Category:Z80 Assembly]]
	[[Category:~~z80~~ Heaven]]		[[Category:Z80 Heaven]]

KermMartian: Created page with "In the last tutorial we pointed out that you can not create permanent self modifying code. So, how do you save important data? The answer is in AppVar..."

2016-02-03T20:05:05Z

Created page with "In the last tutorial we pointed out that you can not create permanent self modifying code. So, how do you save important data? The answer is in AppVar..."

New page

In the [[z80:Application Code|last tutorial]] we pointed out that you can not create permanent self modifying code. So, how do you save important data? The answer is in AppVars. They are a special kind of variable that can only be edited in assembly, and serve as a "permanent" saving point for app data (note that they can be deleted from the memory menu).

= Creating AppVars =

To create AppVars, we will use the _CreateAppVar ROM call. It's inputs are appvar name in op1 and size in HL. Note that when created it will be in RAM.

;omit header
ld hl,AppVarName
rst rMOV9TOOP1
ld hl,32
bcall(_CreateAppVar)

AppVarName:
.db AppVarObj,"AVDATA",0

= Data Structure =

The data in AppVars goes like this: the first two bytes are for size, and then everything else is defined by the program accessing the AppVar.

== AppVar Identifier ==

Generally, it is a very good idea to create an identifier for your AppVar. It can be anything you want and any length you want, so long as your program can identify it later. It is good practice to put it right after the size bytes, but you don't have to if you don't want to.

=== Creation ===

Creating an identifier is as simple as [[z80:Opcodes:ldir|ldir-ing]] into the AppVar.

;load our identifier
inc de ;get over size bytes
inc de
ld hl,identifier
ld bc,9
ldir
identifier:
.db "Identify",0

=== Detection ===

Detection is as simple as checking for any variants between the identifier and the data in the AppVar.

;check for valid AppVar
;assuming de is pointing to start of AppVar Data
inc de ;get over size bytes
inc de

ld hl,identifier
ex hl,de
iloop:
ld a,(de)
cp (hl)
jr nz,invalid
or a
jr z,valid
inc de
inc hl
jr iloop
invalid:
;... in case identifiers don't match
vald:
;... everything matches!
identifier:
.db "identify",0

= Changing AppVar Size =

It's usually a good idea to create AppVars of the correct size to begin with. However, sometimes this isn't possible. So, to do so we just need to insert memory into the appvar and update the size bytes.

;assuming that DE points to size byte and that we have enough memory
push de

push de ;copy de into hl
pop hl

ld a,(de) ;ld de,(de)
ld b,a
inc de
ld a,(de)
ld d,a
ld e,b

add hl,de
ex de,hl ;end of program now in de
ld hl,20 ;insert 20 bytes to the end
bcall(_insertMem)
pop de
add hl,de ;update size
ld a,l
ld (de),a
inc de
ld a,h
ld (de),a

Note that this process is the exact same process you go through to insert memory into program variables, too.

= Conclusion =

AppVars are really useful tools for saving data between application uses. It is interesting to note that regular assembly programs can also access AppVars, and use them in the exact same way that flash applications use them.

{{lowercase}}
[[Category:z80 Assembly]]
[[Category:z80 Heaven]]