[guru_florida]

I am just finishing an FPGA design. It's a basic board with sram, flash rom, sd card, sound codec, +more. It will run a version on ucLinux. It is primarily intended for something else, but I was thinking of using it later as a reference design for cnc control.

If you were to design a dream board for cnc that includes the G-code interpreter and all...would it be with an FPGA (perhaps running linux) or would a cheaper solutions such as an Atmel AVR be more suiting. Maybe a blackfin? The nice thing about the FPGA over AVR is being able to design the stepper or servo PWM in hardware. This is purely opinion but I am interested in a good brainstorming discussion on this.

Initially my cnc machine is controlled by laptop and a amplifier board i bought off ebay. But eventually I would like my machine to be more self contained. I would like to be able to send files to it over the network or usb, and be able to recall programs saved to its memory. I also want a joystick type remote that has digital rotary dials for manually moving the machine and digital read out. All possible with the board I am making.

Second, for those routing pros: In my current FPGA design I have a pcb routing conundrum(??). It's a 4 layer board and I have 3 power supplies. 3v, 2.5 and 1.2. The 3v is is the primarily used supply so it takes the power plane. 1.2v is FPGA core supply only. 2.5v is Vaux provided by a linear reg and will probably be disabled in most of my applications. Good practise tell me not to split the ground and power planes with traces. But I also want to keep my 1.2v (and my Vaux if possible) lines short. So do I route on the power plane my other supplies or route these supplies on the signal plane? I am leaning towards routing them on the bottom layer even though I have them routed on the power planes in the pics. In any case, I will put bypass caps on each 1.2v pin so this should supply the fpga core well with a low impedance source. (bypass caps are not all there in the pics.)

In my pic I dont like how the power lines split the power plan down the middle...if it happened to be at the edge of the board I wouldnt think much of it...but I am thinking of current loop distances.

I have read a really enlightening book on high speed pcb design but I guess I am still a little on the fence.

Colin