ASM Command of the Week

[calc84maniac]

The hidden flags only exist on the old models of the TI-83+, though (the ones with real Zilog chips)

[ZippyDee]

But is there actually any use for the hidden flags? Are the values documented?

[Hot_Dog]

EXX

[Xeda112358]

That is a pretty useful command, especially if you need more registers, or you need to preserve some and you don't use interrupts. I personally rarely use interrupts, so super complicated math functions get to use b'c'd'e'h'l'

So details:
4 cycles, 1 byte, hex code: D9
Swaps registers with shadow registers


So as a really poor example, say I need to copy some data to memory somewhere, but I need to preserve all registers for some reason. Also, assume you don't need interrupts

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di exx ld bc,768 ld hl,BufData ld de,plotSScreen ldir exx

And yay, your registers are preserved

[calc84maniac]

I use shadow BC, DE, HL in all of my intense rendering methods: Project M parallax tilemapper, F-Zero mode7 engine, and TI-Boy tilemapping. (I rarely find a need to use shadow AF, which I would usually give to interrupts).

Also, shadow registers play a crucial role in TI-Boy's CPU emulator, as they hold the Game Boy's BC,DE,HL registers. This allows me to execute many GBZ80 opcodes almost directly, by doing something like exx \ add a,e \ exx in order to emulate add a,e, etc.

[Xeda112358]

Wow, nice, now I see why it is so fast o.o

[Art_of_camelot]

@calc84:That's pretty cool. =)

[chickendude]

Can anyone think of a good use for otd/oti? I just saw JimE's Keyin routine which has a pretty interesting use of ini to store all DI keypresses into saferam that you can access using "bit key,(iy+keygroup)". It's a pretty interesting idea i might implement into some of my programs, especially since you don't have to worry about registers getting overwritten

[Xeda112358]

I have used these commands to read/write data to the LCD ports.

EDIT: For example, if I wanted to draw a simple sprite, assuming the LCD coordinates are already loaded:

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ld bc,0811h       ;b=8, size of the sprite, c=11h, the LCD Data port      ld hl,SpriteData DrawLoop:      <<any code to provide a proper delay>>      outi      jr nz,DrawLoop      ret SpriteData:      .db 3Ch,42h,81h,81h,81h,81h,42h,3Ch    ;ball

[chickendude]

That's what i figured they could be used for, though i was thinking more along the lines of a fastcopy routine. Thanks for the sample.

[thepenguin77]

Let's not forget USB.

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send8BytesBitsOverPipe0: ld hl, bytesToSend ld bc, 8*256+$A0 otir ret

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;####################################### ;take in all the bytes from a port ;input: c = port ;output: b = bytes received importBytes: ld b, 0 importLoop: in a, ($96) or a ret z ini ;this dec's b inc b inc b jr importLoop

Every USB program includes some form of ini/inir and oti/otir. The reason you can do this is because the USB driver has internal buffers and does not need a delay when you write to it.

[Xeda112358]

Hmm, so if I am reading your post properly, the first code sends 8 bytes to port $A0, and the second writes all the bytes being received, to HL, and then returns the number of bytes that were received? Is USB control that easy?

[thepenguin77]

Hmm, so if I am reading your post properly, the first code sends 8 bytes to port $A0, and the second writes all the bytes being received, to HL, and then returns the number of bytes that were received? Is USB control that easy?

The one that reads all of the data is that easy. The driver basically says, "I got some data for you" and you read it all.

The output one is super simplified, but this small section of code does appear in most data transfer code.


USB is super hard.

[Xeda112358]

Okay, I will have to experiment a little with that, then. I don't care to use a standard USB protocol, anyways.

[shmibs]

ooh, are you going to be using it for direct linking between calcs?