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

From: KHMan
Subject: Re: [Tinycc-devel] TCC and ARM instruction set
Date: Thu, 26 Apr 2018 23:20:17 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

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

Kein-Hong Man (esq.)
Selangor, Malaysia

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