Re: [Tinycc-devel] TCC and ARM instruction set

[KHMan]

On 4/26/2018 10:31 PM, Ulrich Althöfer wrote:
> Dear Developers,
> I am interested to hear more about the state of implementing the 
> ARM instruction set.
>
> - Are there different levels of developing states between the 16 
> bit (Thumb) and 32 bit instruction set?
> - Is there a hardware abstraction level (HAL) built in the Tiny C 
> Compiler?
> - Are there documents about this subject?

See this intro: https://en.wikipedia.org/wiki/ARM_Cortex-M

It's like the IA32/x64 instruction set these days, there are a lot 
of different sets of instructions and this and that. What do you 
want to target? That is the question. All? Then the problem is 
complexity and scope.

If you want to target IoT parts, say they use Cortex-M4F, then you 
need to support a bunch of stuff. Supporting a newer arch will 
require supporting other stuff. You kinda need a arch 
infrastructure to keep track of all these things. SAM parts all 
say Cortex-M0+ in their datasheets (that I've read anyway), but 
M0+ is only for the traditional small MCUs.

Anyway, for a C user like me who rarely dip into assembly, it's 
hard to keep track of all this proficiently. Successful chip 
architectures with lots of legacy baggage need a bit of effort to 
learn.


> - How expensive is it to implement the Thumb code?

Projects such as tcc are resource-starved. I'm a lurker, I code 
other stuff, but I'm sure coders are welcome here. There are no 
troops to rally. It's more roll up your sleeves and dig in.


> - Isn't it a challenge to implement the 'tiny' Thumb instruction 
> set, because ARM is the overwhelming dominant embedded processor 
> architecture nowadays?

Not all embedded users need Thumb instructions. The ARM arch has 
different 'modes' targeted towards different market segments.

If you want to be on the leading edge of something, why not do 
RISC-V instead?


> I am glad to hear about the intentions of implementing.
>
> Greetings from Germany
> Ulrich


--
Cheers,
Kein-Hong Man (esq.)
Selangor, Malaysia