On 28/06/2018 17:55, Pabst Blue Ribbon wrote:
> Gareth's Downstairs Computer
>  wrote:
>> On 28/06/2018 17:17, Pabst Blue Ribbon wrote:
>>> The Natural Philosopher  wrote:
>>>> On 27/06/18 21:00, Peter Percival wrote:
>>>>> Gareth's Downstairs Computer wrote:
>>>>>> On 27/06/2018 20:23, Peter Percival wrote:
>>>>>>> There seem to be a number of Forths that run on Raspberry Pi.  Is it
>>>>>>> possible to say which one of them is best?
>>>>>>
>>>>>> The one that you write for yourself?
>>>>>>
>>>>>
>>>>> Would that I could!
>>>>>
>>>> An actual FORTH 'kernel' is very easy to write.
>>>
>>> I can be even more specific. On x86, 'kernel' is just 4 (four) processor
>>> instructions. The rest can be treated as 'library'.
>>
>> ISTR that on the PDP11, it was just a single instruction ...
>>
>> JMP @(r0)+
>
> I'm not familiar with PDP11. Four instructions I was referring to was
> complete NEXT statement from my simple Forth system. Single instruction
> versions that I've seen on Z80 were basically jumps to NEXT statement which
> was kind of outside of the rest of Forth (and which was still bigger than
> one instruction). I guess it all depends on which registers are used and
> which instructions available for the programmer.
>

It is some years since dabbling with FORTH on X86, but ISTR using SI as
the pointer to the current brick, when the kernel code (actually
added to the end of each primitive operation becomes just 2 instructions ...

LODSW
JMP AX

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