Re: Adapting an Ada compiler to generate 8051 code (Again?! ;-)

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 2021-03-31 0:28, Luke A. Guest wrote:
> On 30/03/2021 20:16, Paul Rubin wrote:
> 
>> Besides the approaches other people have mentioned, I don't know if
>> there are any really large obstacles to targeting GCC to the 8051, or to
> 
> The biggest obstacles will be the severe lack of registers. But it's 
> possible, lm78 for example.


The 8051 is not very register-poor: it has a main accumulator and a 
secondary accumulator and four sets of eight general-purpose registers. 
The 32 general-purpose registers occupy the first 32 bytes of the 
internal data memory. A compiler could also use all of the directly 
addressable 128 bytes of internal data memory as registers, although the 
instructions that can use those "registers" are a little longer and a 
little slower.

If there is a problem for gcc, it may be that all those registers are 
only 8 bits wide, and cannot be used to address external data memory 
(although some of them can be used as 8-bit offsets in paged memory 
accesses). Only the Data Pointer Register (or registers, in newer 
variants) is wider and can be used to address external data memory.