A89: Re: Various 68K/TI89 things

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A89: Re: Various 68K/TI89 things


> As a Z80 programmer trying to learn 68K, I wonder about a few things.
>
> First, what is this stuff about handles and the heap?  Are handles sort
> of like they work in Windows, where they provide a number that represents
> a system object?  How large is the heap?

A handle is an index in a table of pointers. The purpose of them is to make sure
you can find a memory block again after a memory clean-up.

> Second, why doesn't the 68K like odd addresses?  Do the assemblers
> basically handle this for you, because I don't see very much use of the
> EVEN directive.

It's just designed that way (to make it faster, IIRC - it's not exactly a new
processor). As for EVEN, if you have a section if data that consists of
words/longwords you'd better put the EVEN directive before it to avoid address
errors.

> Third, although the 89 ROM was much larger than any of the Z80 ROMs, I
> think the C programming is screwy for ASM programmers because you have to
> push arguments for ROM calls. I admit that this method has its
> advantages, but it is mostly annoying.

The system was never designed with ASM programming in mind. Pushing arguments
onto the stack is standard for processors of this type.

>  In addition, I think the ROM
> could have been written much more reliably.  I have never had so many
> calculator crashes related to Line 1111 Emulator errors and things like
> that.

Line 1111 Emulator errors are most likely your own fault as they occur when you
try to execute non-instructions.

>  It gets so annoying.  I have to take a full calculator back up
> every time I add a game to my calculator to make sure I can still recover
> my programs after the inevitable crashes.  I'm still angry that you lose
> your archive memory in addtion to the normal memory, although I can see
> why.

Well, that's hardly the CPU:s fault... :o)

> Also, why is this language so ugly?  It just looks terrible compared to
> Z80.  You might think they would have logical mneumonics, and instead of
> packing all 13 or whatever different address modes, have different
> mneumonics for them.  For example, I like my imaginary instruction:
>
> PUSH.W d0,(a0)
>
> much better than:
>
> MOVE.W do,(a0)-
>
> It makes it much easier to remember commands.  I think I'll just leave
> the ASM up to TI-GCC

As with any language it's something you get accustomed to... the Z80 and 68000
are two different types of processors, after all: the Z80 has an accumulator
structure whereas the 68000 is based on general-purpose registers.

In this particulat case you should be able to write a macro that lets you write
PUSH instead, though.

I personally think Z80 is ugly, but I haven't programmed anything in it and
don't want to start a flame war on the list :)


 / Niklas Brunlid
Check out Prosit for the TI-89 / TI-92+ at http://prosit.ticalc.org
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