[Coco] OS9 vs Flex

[John Kent]

On 2/01/2012 8:09 PM, John Kent wrote:
>
>
> The point of designing the FPGA 6809 was to learn a little about CPU 
> architecture. You can still demonstrate principle of multiprocessing 
> and caching with a simple 8 bit CPU. I'm not sure if it is possible to 
> turn the 6809 design into a Harvard architecture where it can be 
> accessing data at the same time as it is fetching instruction opcodes 
> out of cache.
>
> John.
>

The advantage of the 8 bit design is that you don't need a big expensive 
FPGA board. You should be able to implement a 4 core 6809 in a XC3S1000 
FPGA. You use block RAM as cache to reduce the memory bandwidth 
requirements for main memory. You can implement interrupt driven 
inter-processor communications. I'm not sure why you'd want to do that, 
but there may be reasons such as low latencies on interrupt or device 
handling.

If you can have separate processors servicing I/O in parallel it reduces 
the time between servicing events and I/O can overlap. Processors can 
share common instruction code while having their own data segments.

John.

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