Re: Test suite for 6509 processor

From: Michał Pleban <*lists_at_michau.name*> Date: Sun, 25 Feb 2018 23:41:57 +0100 Message-ID: <5A933BB5.1080308@michau.name> · lists_at_michau.name

Mia Magnusson wrote:

> Or use indirect access to 0/1?

A side note - the fact that indirect access to these addresses will
still affect CPU registers is the reason why disk reads do not work
across 64 kB boundaries in the 6509 MS-DOS IPC library.

Interestingly, the IPC code contains specific workarounds in case the
read crosses such boundary (rewinding the memory pointer to 0000 and
incrementing the $1 register value) but they are worthless anyway
because as soon as anything is written to memory address $x0000,
everything goes out of the window. It is apparent that the programmers
who wrote this code did not understand fully how the 6509 works.

Regards,
Michau.

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