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Several people asked me what I plan to do next on this A2Z project.

Probably nothing, I will explain why. 

Porting Linux ? Retargeting a compiler?

What A2Z is not:

This question was asked several times. Some people consider A2Z as a 100% open source platform which could run a 100% open source Linux. They are wrong, I will explain that.

There is a misunderstanding.

I’m afraid, Linux and a C compiler is totally not feasible.

A2Z lacks many things to achieve the goal of C retargeting and Linux porting.

• A2Z only manages Direct Addressing in hardware. No complex address computation. If you want to implement data stack, recursive functions, then direct addressing is not enough. You cannot retarget a C compiler with only direct addressing (or if you emulate complex addressing modes by software, it would be very very slow).
• A2Z has not interrupt management. You cannot implement/port a pre-emptive multitasking OS (Linux) without interrupt management.
• A2Z has no memory management unit.
• A2Z’s ALU is compatible with nothing.
• Etc…

What A2Z is :

A2Z is “just” a very simple and didactic project. The DIDACTIC aspect is the most important.

When I started this project in my mind 3 years ago, the goal was to make things very simple, and start from a blank page. I didn’t want to copy other CPU architectures.

I didn’t want to take the constraints of “being compatible”, or using one existing compiler / language. I wanted a lot of freedom in this project.

Therefore, A2Z is compatible with… nothing.

I don’t think that lots of people have made such usable computer starting really from scratch, from a blank page.

I’m very proud of the result.

Anyway, What’s going next?

I consider A2Z totally finished, so there will be nothing more on A2Z project.

Of course, I have several ideas to improve the A2Z, with the same principle, the same CPU architecture. There is a list:

• Accelerate to 50MHz (currently 25MHz) : I know that it is feasible
• Instruction cache : I could put an instruction cache inside the FPGA, and switch to a faster “Harvard” architecture when the CPU uses it
• Small pipeline : Now that the pipeline concept is clear in my mind, I could improve the CPU with a small (2 steps) pipeline
• Flexible CPU state machine : the state sequencer of the CPU core is currently too simple, too rigid, and wastes a lot of cycles. Making a flexible state machine could improve the computing power.
• Video part : 2D hardware acceleration with sprite management
• Reprogramable graphics palette (256 colours out of 4096) for better pictures rendering
• Ethernet and networking : The idea would be to code a very simple Ethernet card directly inside the FPGA.

BUT… I will not make any of these improvements. I simply don’t have time, and I have already moved to other projects. Robotics and amateur radio projects (F4HDK is my amateur radio callsign).  Even if I come back to CPU architecture study sooner or later, it will be with a brand new project.  

Your turn!

But I remind you that all the source code is freely available for download, everythink is open source. So you can play with it, improve it. I will be very happy if someone proposes improvements for A2Z. Of course, I can bring support about topics that I have not well documented.