Stack Requirements

[James_Parsons]

http://www.devili.iki.fi/Computers/Comm ... e_274.html

what does it mean
Stack Requirements: 13

[BigDumbDinosaur]

James_Parsons wrote:

http://www.devili.iki.fi/Computers/Commodore/C64/Programmers_Reference/Chapter_5/page_274.html

what does it mean
Stack Requirements: 13

It means that the maximum stack space consumption during the subroutine call (ACPTR) is 13 bytes. An additional two stack bytes are used for the return address back to the calling program, which Commodore did not count as part of the kernel call's stack usage. ACPTR itself makes various internal subroutine calls to handshake the serial bus, which is where some of that stack space gets used.

Although the 6502's stack is tiny by current standards it can handle quite a few nested subroutines. Assuming the worst case, in which each subroutine pushes all registers for later restoration, 42 subroutines can theoretically be nested. I say "theoretically" because interrupts will also claim stack space. Plus when BASIC is running, the stack gets used for FOR-NEXT loops, as well as handling GOSUB-RETURN pairs. You can get an OUT OF MEMORY error in BASIC if too many GOSUBs or FOR-NEXT loops are nested. The choice of error for this situation is unfortunate, because there's plenty of memory when it happens. What is really happening is that the stack pointer has been driven too close to $00, leaving insufficient stack space for another GOSUB or FOR-NEXT.

[GARTHWILSON]

From this page, it appears to be how many bytes' space it takes in the hardware stack (which is in page 1), not including the return address that gets put on it by your JSR that calls the routine. 13 bytes on that one is extraordinarily heavy stack usage. I looked at a lof of the following pages, and the other routines all took less, mostly zero to two.

It looks like you found a really good website there!

[barrym95838]

GARTHWILSON wrote:

... It looks like you found a really good website there!

That guide is a classic ... I still have the paper-and-ink version (well worn from extensive use in 1984) on my bedroom bookshelf.

Mike

[BigDumbDinosaur]

barrym95838 wrote:

GARTHWILSON wrote:

... It looks like you found a really good website there!

That guide is a classic ... I still have the paper-and-ink version (well worn from extensive use in 1984) on my bedroom bookshelf.

Mike

At one time I had it memorized. Time and some failed synapses have forced me to start reading again.