Getkey

[yugniht]

I've written at least a couple of programs where I'll have a lot of code then a getkey. Let's say I press the number 9 while my program is drawing a bunch of stuff, for example. Then, when the program gets to the getkey, 74 is automatically what the getkey returns, even though I pressed the button before the program encountered the getkey.

Does anyone understand what I just said? Moreover, does anyone know why it does this?

[Darth Android]

im not an asm guru, but i asume the calc just buffers the byte until it needs it. i know the keyboard has its own personal buffer, though it is small.

[yugniht]

buffers? You've lost me. All I know is that I can press a button before getkey is executed and it will recognize that button.

[Arcane Wizard]

A buffer is a (often small) part of the memory that holds some temporary data.

This is how it helps cd-writing for example:

When writing a CD, the data has to be written continuously, i.e. there may be no breaks in the data flow. As of course the computer can not supply a constant stream of data (it transfers it block by block), the CD recorders have got a buffer which temporarily stores the data send by the computer and then sends it on to the writer at the correct speed.

If the computer does not manage to keep refilling the buffer during the write process (i.e. the buffer is emptied completely), then the write laser does not have any more data to write so the write process has to be interrupted.

[Darth Android]

i believe the keyboard buffer is 1 byte cuz it only stores one keypress...
do you agree?

[Arcane Wizard]

Sounds logical, but I don't know enough about buffers.

[Darth Android]

well, im learning asm, so i need to know more about them. not that i do (key work: need)

[Arcane Wizard]

Make a topic about it on the asm board.

[Darth Android]

that sound the most logical. i will do that when ready

[Adm.Wiggin]

a buffer is usually just a fairly small database... the one for the norm. keyboard is probably 1 or 2 bytes like you said... but the TI-Keyboard buffer (not in the keyboard must build in urself in asm prgms) is 17 bytes or something... it needs 2 bytes for each keypress though...

[Darth Android]

well, that would make it reasonable for the keyboard's buffer to be 2 bytes, then

[Adm.Wiggin]

i meant 2 bytes for each TI-Keyboard keypress... not normal keyboard... it only needs 1...

[Darth Android]

oh.. i misread what u typed (i need to clean my lenses) ill read more careful next time

[Justin W.]

My guess is this. While executing a basic program the TIOS is running an interupt that tests for a keypress. A one byte buffer would be in place for storing the keypress. Now if no key is pressed the byte would be 0. If a key was pressed it would be stored into that buffer. Now it would not overwrite it because the value is not zero. Hence the reason you can press a key and it registers as soon as it encounters the getkey command.

I have a good knowledge of asm and this is just my guess.

[NETWizz]

The interrupt is IM 1, ad it is located at 38h but doesn't really start until 3ah. It then jumps to 6ah.

Anyway, anytime a key is pressed, a two byte value is saved in a buffer because some keys are two bytes. For example, press 2nd then a key to get a different key code.

Now, in reality the interrupt uses direct input to do getcsc, which in turn is used by getkey (asm).

Your getkey in basic is a romcall (not bcall(getkey) btw) which is grabs the two byte scan code from getcsc.

Getcsc is essentially direct input where you press the key and it saves the code, and the hardware forces a flag when anykey but on is pressed.

Basically, when this flag is set, the buffer will change to 0 and stop returning the key, so your keys do not repeat.

If TI wanted, or if you were really good at IM 2, you could make your own keyboard device driver to make all your keys repeat. e.g. hold down the 9 key and get 9999999999

[Darth Android]

yeah, i wish u could hold down keys other than the arrow keys and the del key.

BTW, JBirk, do u remember the getkey prgm u were going to make back at the cirrus forum?
if was going to use direct input to detect for multiple keypresses and output like this:
for [2ND]+[DEL]: 21.23
[ON]+[CLEAR]: 101.45
[1]+[3]: 92.94

remember?

[Adm.Wiggin]

i remember...

it wouldnt be too hard to make the interrupt... just have it use direct input and save the Direct Inputted key in the buffer...

[Darth Android]

and using getkey->variable would reteive it? could it pick up the [ON] key to?