criteria when selecting next MPU

[Werner Almesberger]

Ron K. Jeffries wrote:
> what is consensus on level of performance bump
> is needed for next Freerunner?

Ah, that's what we call the "CPU" now :) (Used to be "MCU", but since
we also have a PMU and now an MPU, that's too close for comfort.

We're basically constrained by what chips we can get. We decided to go
with Samsung again, since we perceive this to have the lowest design
risk for us. GTA04 will have a Samsung 6400. Clock rate will be roughly
the same as in GTA02, but the ARM core is more modern (ARM11 instead of
ARM9), which brings a number improvements.

However, the big difference will be that we move the video RAM back to
the CPU, similar to what we had in GTA01. In GTA02, we use a dedicated
accelerator chip for video, but it turned out to be actually slower for
many operations than if we had just attached the LCM to the CPU, because
the bus between CPU and accelerator is slow, and also because the GTA02
has better main memory bandwidth than the GTA01.

The 6400 CPU in GTA04 will be even better, with much faster memory and
graphics acceleration operations in the CPU. All this together should
make graphics a lot snappier.

It's much too early to tell how fast things will really be (it's a
question of the mix of operations), but there should be a substantial
improvement for graphics. (Finally ;-)

- Werner