Re: [CAD_CAM_EDM_DRO] Re: CAM Software Advice for Shopmaster CNC, ARM7, USB

Alan KM6VV wrote:

> Hi Jon, Wayne,
>
> Heard you on AT91SAM7 list! The Atmel demo board for the AT91SAM7S256 board
> is nice, if pricy. I've designed a controller board (industrial laundry)
> using the chip, and interfaced an APA LCD (128 x 64), a few keys, and 16
> inputs and outputs (via SPI), as well as RS485. Also USB Host and Device.
> This is a very well supported chip!
>
> I've got my eye on it for possible inclusion on a hexapod robot. One could
> implement quite a lot on this uP for CNC as well. The SAM7X part has
> Ethernet, I'm told. With -S you get USB Device.
>

Yes, not only 10-base-T but 100 Mbit Ethernet, too. The chip
has the MAC with the media independant interface, and a (I
think) $3.00 chip and a $6 transformer+connector is most of the
remaining circuitry. So, roughly $25 in parts will get you the
CPU and the complete Ethernet hardware.

> If you want a cheap (tiny) platform with the uP on it, Spark Fun has the
> Olimex SAM7-H256 "header", complete with a USB connector and regulator. Now
> THAT would make a good USB dongle!

I need a high speed path to the host PC, so it is looking like
USB high-speed or 100 Mbit Ethernet at the least. There is some
serious concern about the performance of the Ethernet protocol
driver on the AT91SAM7X. Some people who have implemented it
said it couldn't handle over 1 thousand packets a second. That
sounds pretty serious. Maybe if the protocol was simplified and
a bunch of feaures were turned off, switch to UDP instead of TCP
and so forth, the overhead could be cut. And, of course, there
is the final "terminator" approach, kill everything in sight and
turn both ethernet ports into basically UARTs, remove
practically all the overhead. You will only have one unit on
each end of the wire, every message received IS for you,
collisions on a full-duplex point-to-point net are impossible,
etc. Using this aproach, yes it is totally non-standard, but I
would think the entire exchange could be done in about 15 us.
Giving the PC enough time to crank the PID processing in the
middle should still get it down to 50 us on a decent PC,
allowing the goal of a 10 KHz servo update cycle to be possible.

Jon