Re: Apple IIe TCP-IP w/ LANceGS Card

[mjmahon@aol.com (Michael J. Mahon)]

Marsha replied:

>mjmahon@aol.com (Michael J. Mahon) wrote in
>20031220012012.03823.00001381@mb-m07.aol.com:">news:20031220012012.03823.00001381@mb-m07.aol.com: 
>
>> I don't think there would be much simplification, since one set of
>> software is "firmware" and the other is driver software.
>> 
>> Except for religious reasons, they might just as well used a Z-80 for
>> the card.
>
>Except, some of the driver code in the ROM is code that appears in the slot 
>for the motherboard to execute.

Of course, but it is not difficult to "paste together" code for different
machines in a ROM image--it wouldn't take much of a make file.

If the two machines are a 65C02 and a 6502, then all that needs to
happen in the 6502 code is the exercise of discipline.  ;-)

>Looking at the code, there is liberal use of STZ and BRA... 
>and while sometimes the programmer knows and/or doesn't care what the 
>existing registry flags are, often they are significant and need to be 
>preserved.

I have no doubt that if the programmer was thinking this way, he or she
has come to be dependent on the extra ops.  But I must reiterate,
in _most_ cases, enough is known _a priori_ about the state of the
processor that little or no additional code is required.  In those few
cases where the A register must be used to store a zero, for example,
the worst case scenario is adding a PHA and PLA around the LDA #0
STA foo.  I have also found that INC and DEC can often be used to get
the advantage of STZ for "flags" without using the op.

>Considering the cost of the workstation card at the time, a drop in 
>replacement 65C02 for the motherboard wouldn't have been that much of an 
>investment.

I certainly agree that the gross margin on the Workstation Card was
typically high, but including another processor, and requiring a user
(maybe a teacher) to pull a processor chip and replace it would have
been a big mistake.  Much better to use 50-60 more bytes of ROM.  ;-)

-michael

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