Re: 6502 stack register at reset

From: Spiro Trikaliotis <*ml-cbmhackers_at_trikaliotis.net*> Date: Sat, 25 Nov 2017 22:39:38 +0100 Message-ID: <20171125213938.GE7692@hermes.local.trikaliotis.net> · ml-cbmhackers_at_trikaliotis.net

Hello,

* On Sat, Nov 25, 2017 at 09:35:18PM +0000 smf wrote:

> The commodore 64 kernal sets the stack pointer & they did a lot of rewriting
> to make it fit in the limited rom. So if it was unnecessary then it's 3
> bytes they could have removed easily.

Here, it is different.

The C64

- does calculations to find out of the stack overflows (because you have
  to many gosub, for)
- restores the stack pointer at some places to have a known value
  ("reset" it)

Here, it helps to know where the stack begins.

Likewise, the 1541, for example, only uses part of page $01 for the
stack pointer. Thus, it has to initialize it, too.

Regards,
Spiro.

-- 
Spiro R. Trikaliotis
http://www.trikaliotis.net/

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