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The most common way to address a 16-bit I/O port on the Z80 is to load the BC register pair with your port address, then issue the OUT (C),A instruction, like this:
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LD BC,$BF3B ; register select port
OUT (C),A ; send contents of accumulator to portNo, because you need to address two different ports, the register select port and the data port. On top of that, OTIR uses the B register for the loop counter, so your port address would get clobbered.
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ld hl,(23730) ; RAMTOP
ld de,(23653) ; STKEND
; RAMTOP-STKEND is the memory remaining
and a ; reset flags
sbc hl,de ; or SBC HL,BC
; result remains in HL - must be transferred to BC
ld b,h
ld c,l
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ld hl,(23730)
ld de,(23635)And it did!
Exactly what I was looking for. Congraturation, Well mown, corned beef sandwich, A Winner Is You, etc etc etc etc etc. You all know the drill by now.LD BC, (23730)
CALL 11563 ; CONVERTS BC TO 5-BYTE NUMBER AND PUSHES TO CALC STACK
CALL 11747 ; Print and clear top of Calc Stack
LD BC, (23635)
CALL 11563 ; CONVERTS BC TO 5-BYTE NUMBER AND PUSHES TO CALC STACK
CALL 11747 ; Print and clear top of Calc Stack
Not sure if this helps: I use this small code to set palettes:TMD2003 wrote: ↑Fri Jan 15, 2021 1:40 pm Time for a mild bit of thread necromancy, I reckon. Before what was Christmas for just about everyone else, I was looking into ULAPlus to experiment with the new colours it could produce. It requires the OUT command with two two-byte values to start the routine and redefine the colours.
Instantly I thought of writing simple machine code routines to achieve the same thing - but I went back to the Machine Code Tutor and the OUT opcodes only handle one-byte values. What's the workaround, because there surely must be one (otherwise titles such as the ULAPlus version of Subacuatic would never have existed). Also, if I'm redefining the entire palette, is this something that the OTIR opcode might be useful for - say, store all the required codes in successive addresses and then OTIR them in one shot rather than OUTing them one by one?
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;set a 64 colours palette for
;the ULA+
;save the binary as "64c.pal"
;+3code
;
org 44084
;ULA+ on
;this is equivalent to BASIC
;OUT 48955,64: OUT 65339,1
;
ld bc,48955
ld e,64
out (c),e
ld bc,65339
ld e,1
out (c),e
;counters
ld hl,data
ld d,64
dec hl
;loop
rut1:
inc hl
;this is equivalent to the BASIC
;OUT 48955,d: OUT 65339,a
ld bc,48955
dec d
out (c),d
ld bc,65339
ld a,(hl)
out (c),a
jr nz,rut1
ret
;here the values for the palette
data:
defb 0, 0, 0, 0, 0, 0, 0, 0
defb 0, 0, 0, 0, 0, 0, 0, 0
defb 0, 0, 0, 0, 0, 0, 0, 0
defb 0, 0, 0, 0, 0, 0, 0, 0
defb 0, 0, 0, 0, 0, 0, 0, 0
defb 0, 0, 0, 0, 0, 0, 0, 0
defb 0, 0, 0, 0, 0, 0, 0, 0
defb 0, 0, 0, 0, 0, 0, 0, 0
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5 CLEAR 44083: LET org=44084
7 LOAD "64c.pal" CODE
10 DIM a(64)
15 REM reading palette from ULA+
20 FOR b=1 TO 64
30 OUT 48955,b-1
40 LET c=IN 65339
50 LET a(b)=c
60 NEXT b
90 LET e=65
100 FOR d=org+36 TO org+99
105 LET e=e-1: POKE d,a(e)
120 NEXT d: INPUT "File name:",a$
125 PRINT "Saving palette ";a$
130 SAVE a$ CODE org,100
I used HALT to synchronise the frames and my drawingDisabling or minimising .. I want the Interrupts for timing, but my interrupt code consists ofAndyC wrote: ↑Mon Mar 28, 2022 10:17 am Well the ROM routine does everything "right" so as long as you aren't doing devious things with the stack or messing with IY and the alternate registers (which the Speccy OS reserves) you kind of can pretend interrupts don't exist.
But if you want access to all the registers or want to start doing more stack manipulating, then you do at least need to embrace disabling interrupts.
What I was really trying to say was, this is something so far beyond my level that I cannot even attempt to use it yet. If the entire concept of interrupts can be likened to the final year of a Masters degree, I am still working my way through primary school - and it is very, very unlikely I will ever get even close to this level.
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10 LET z$="VQFods634#%&"
20 LET a$="": LET b$="": LET c$="": LET d$=""
30 DIM l(4)
40 FOR n=1 TO 4
50 LET l(n)=INT (RND*11)+10
60 NEXT n
70 PRINT "LENGTH OF A$ = ";l(1)
80 PRINT "LENGTH OF B$ = ";l(2)
90 PRINT "LENGTH OF C$ = ";l(3)
100 PRINT "LENGTH OF D$ = ";l(4)
110 FOR n=1 TO l(1): LET z=INT (RND*12)+1: LET a$=a$+z$(z): NEXT n: PRINT "A$ = ";a$
120 FOR n=1 TO l(2): LET z=INT (RND*12)+1: LET b$=b$+z$(z): NEXT n: PRINT "B$ = ";b$
130 FOR n=1 TO l(3): LET z=INT (RND*12)+1: LET c$=c$+z$(z): NEXT n: PRINT "C$ = ";c$
140 FOR n=1 TO l(4): LET z=INT (RND*12)+1: LET d$=d$+z$(z): NEXT n: PRINT "D$ = ";d$
150 INPUT "Q$ = "; LINE q$
199 REM view variables area
200 FOR n=(PEEK 23627+256*PEEK 23628) TO (PEEK 23641+256*PEEK 23642)-1
210 PRINT n;" "; INK (2 AND PEEK n<32);PEEK n; INK 0;TAB 12;CHR$ ((32 AND PEEK n<32)+(PEEK n AND PEEK n>=32))
220 NEXT n
Well, the concept is pretty simple. An interrupts is an electrical signal; that is to say, it happens on the physical level, and the CPU has a whole pin (well, two pins, in fact) to detect it. How to deal with it when it occurs is up to you. You can even tell the CPU to ignore it altogether (DI stands for Disable Interrupts) and go on your merry way. Much like you can decide what to do when your phone rings when you’re in the middle of something: you can turn the sound/vibration off (“disable interrupts”), let it go to voicemail, or answer it.
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...
400 IF phone_ring=1 GOSUB 900
...
...
900 REM deal with a phone call
...
1100 RETURNHonestly, interoperating with BASIC is one of the more complex things you can do in machine code, because the BASIC interpreter is actually a pretty complex system.TMD2003 wrote: ↑Mon Mar 28, 2022 9:45 pmWhat I was really trying to say was, this is something so far beyond my level that I cannot even attempt to use it yet. If the entire concept of interrupts can be likened to the final year of a Masters degree, I am still working my way through primary school - and it is very, very unlikely I will ever get even close to this level.
But nevertheless, I thought I'd attempt something more challenging - something I have yet to tackle and (more to the point) is something I'll find useful.
It's how to handle BASIC variables via machine code.
To put this in context, I've also been re-typing all of the 40 Best Machine Code Routines, and some of those late in the book access the variables area.
All I know so far is: the variables area starts at the address held in VARS and ends at one less than the address held in E_LINE. And while I still have trouble decoding the way that numerical variables are held (mainly because they're all five-byte floating point values that are also beyond my level at this stage), string variables I can see by PEEKing this area.
I see: the letter of the variable, always as a capital, then two bytes for the number of characters, then the characters themselves. Superficially, it seems easy to search for a particular string variable.
So I have started with this BASIC program that should test whether or not there is a method that is absolutely failsafe in finding a required string variable. I have chosen to look for Q$.
To cause the maximum number of hurdles, I've set up the following:
- Define a string Z$ with twelve characters in it, one of which is Q.
- Define four blank strings A$-D$.
- Define an array L(4) into which random values between 10 and 20 are inserted.
- Populate A$-D$ to a length of L(n) (n=1-4 corresponding to A$-D$), with the characters from Z$. It is likely that all of these will contain one or more Qs.
- INPUT LINE Q$, which defines the string I will search for.
- (eventually...) Execute the machine code routine, search for the variable Q$ and have my evil way with it.
So far, all I know is:Code: Select all
10 LET z$="VQFods634#%&" 20 LET a$="": LET b$="": LET c$="": LET d$="" 30 DIM l(4) 40 FOR n=1 TO 4 50 LET l(n)=INT (RND*11)+10 60 NEXT n 70 PRINT "LENGTH OF A$ = ";l(1) 80 PRINT "LENGTH OF B$ = ";l(2) 90 PRINT "LENGTH OF C$ = ";l(3) 100 PRINT "LENGTH OF D$ = ";l(4) 110 FOR n=1 TO l(1): LET z=INT (RND*12)+1: LET a$=a$+z$(z): NEXT n: PRINT "A$ = ";a$ 120 FOR n=1 TO l(2): LET z=INT (RND*12)+1: LET b$=b$+z$(z): NEXT n: PRINT "B$ = ";b$ 130 FOR n=1 TO l(3): LET z=INT (RND*12)+1: LET c$=c$+z$(z): NEXT n: PRINT "C$ = ";c$ 140 FOR n=1 TO l(4): LET z=INT (RND*12)+1: LET d$=d$+z$(z): NEXT n: PRINT "D$ = ";d$ 150 INPUT "Q$ = "; LINE q$ 199 REM view variables area 200 FOR n=(PEEK 23627+256*PEEK 23628) TO (PEEK 23641+256*PEEK 23642)-1 210 PRINT n;" "; INK (2 AND PEEK n<32);PEEK n; INK 0;TAB 12;CHR$ ((32 AND PEEK n<32)+(PEEK n AND PEEK n>=32)) 220 NEXT n
- LD HL,(23267) / LD DE,(23641) / DEC DE will set the start and end points of the variables ares where I want them (unless I find it's a better idea to use IX instead of HL, which it might be). If I was then to LD A,(DE), A would read 128. (Or at least, it should, if I've done everything right.)
- At some stage there will be CP 81, followed by JR NZ (backwards) to cycle round until we reach a Q... then we get to the tricky bit.
And that tricky bit is: how do we establish beyond any doubt that the Q we're looking at is the one we want? There is at least one Q in the variables area (within Z$) and another unspecified but probably non-zero number of Qs after that, before we get to the Q that signals that this is the variable Q$.
You may say "Aha! Look at the value immediately after it!", but there's a problem. In this case, all the Qs in Z$ and the junk variables A$-D$ will be followed by values between 32-128, but in a general case that won't necessarily be true; there may be control characters inside other string variables with values under 32. And likewise, there's no guarantee that the value after the Q we want will be under 32, because the string length can easily be 32 or more, or greater than 288, or...
It must be possible, because every time BASIC recalls Q$, the ROM routine to do so always knows exactly where it is.
Once this has been sorted out, I can make some very rudimentary string handling routines, even if it's something as mundane and milquetoast as a ROT13 encoder, or reversing the order of the characters, for a string Q$ of any length.
So far, if I want to do anything like this, I have to resort to a bit of BASIC to POKE the CODE of each character into a series of addresses above RAMTOP, before I can do what I want with them. And now that I think of it, this is what I had to do on Super Mario Fruit Machine 2; my bit of machine code to print all the reels on screen was supposed to speed it up significantly, but the four POKEs required for each character, of which there were nine, robbed the game of most of the speed bonus. While it might have been possible to hold all the reels as a series of bytes above RAMTOP and then write an easier routine to access those without having to probe the variables area, either I didn't think of that at the time or had already invested too much time into making it work the BASIC way that this would have required a significant rewrite (and the fact that I wrote the game using BASin probably doesn't help on that front).
If I needed to use IY in a routine called from BASIC, is it likely to work if I start the whole thing with PUSH IY and then POP IY before the final RET?