Subject:
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Re: Some comments (long) (was: Something else is needed, I think...)
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 7 May 1999 00:31:34 GMT
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Viewed:
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1395 times
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Chris Phillips <chris.phillips@computerboards.com> wrote:
> Do you think it would be possible with improved firmware to support
> inline H8 code embedded in a user program? For example, a special byte code
> could indicate that the following code should be executed directly by a
> subroutine CALL until it decided to RETurn? This might allow compilers to
> embed high-performance, efficient library code into a user program instead
> of relying on the firmware to implement every feature, or byte code
> operations to support every possibility.
You might be able to do this if you were clever about it; you might be able
to define an opcode that defines a native subroutine that you can call with
another opcode, say, that passes in 16- or 32-bit values in registers and
expects you store the result in registers also, something like how the math
routines work now. Somebody mentioned position independent code (or the
lack thereof); the RCX doesn't support this well because PC-relative
branches only have the range of a signed char. GCC at least uses absolute
jumps in place of longer branches.
I think inserting native code is getting a bit overkill, but that is just
my $0.02.
> I'm not surprised that MulDiv isn't supported directly by the H8. But do
> you know if the H8's MULtiply instruction returns a 32-bit value? (On
> 16-bit 80x86 processors, for example, this is done using two registers: AX
> for the low word and DX for the high word of the result.) I believe that
> this would be a requirement for implementing a MULDIV byte code on the RCX.
Actually, the H8 is worse than this. It only supports 8-bit multiplies,
storing the result in a 16-bit register. 16-bit and 32-bit operations are
supported in software by routines located in ROM.
> > - have you considered writing native code?
>
> I actually have considered writing native H8 code. Unfortunately, I have
> been stymied by several factors:
I asked the question because, from the things it sounded like you wanted to
do, LegOS might be a better development environment for your needs. Then
again, you are clearly one of the people who is running into trouble with
the development environment, which can be a complete pain. (I know how it
is, it took me a while to get it set up on my everyday machine.)
Also, that you want to do firmware development also means you need to get
over the hurdle :)
-Kekoa
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