[evla-sw-discuss] MIB Study Group-Search for the MIB Processor

[Wayne Koski]

In this opening salvo, I wish to put down why I'm somewhat enamored on
using the EC-1.  As part of the study group, I'll be carefully looking at other
possibilities based upon what I like to look for in such a device.

So here is the EC-1 in a nutshell:  * = Key Items of interest, prioritized. 

*A flexible Boot methodology using a 2K on-board boot loader.
*256Kbytes Static RAM.
*Ethernet MII interface.
*8K bytes of dual port RAM
*A SPI Interface.
*16M Bytes address space.
*Two UARTS.
*26mm x 26mm x 1.5mm
JTAG
Watchdog Timer.
Three timers.
Four DMA methods.
Simple chip select logic.
Two CAN Interfaces.
Intel 186 derivative.

As you can see, my interest lies in the ease of loading and executing software,
followed by methods of interfacing.  Surprising enough CAN wasn't a major
factor, but was a nicety in that it could cover usage of ALMA modules during
hardware development.  The processor being based upon the Intel 186 was
also a nicety as we have people in the M&C lab who have knowledge of this
device.

What is missing from the EC-1 was internal Flash that would hold the
Operating System (RTOS).  But, given the fact that the EC-1 had 256K in it,
I hoped that the RTOS + MIB application core would fit in it.  All I needed to
do was to load everything from an external serial flash.  However, I did allow
for 2M of flash plus 1M RAM to cover a probable underestimate of software
requirements in my design.

Therefore my main attraction to the EC-1 was that the amount of external parts
required to build the MIB was low.  And the external complex parts were the
physical Ethernet devices and memory.  The rest of the design were serial
translators for RS232, RS485, and CAN.  Add to that buffers and simple glue
logic and thats the design. On-board A/D or D/A would add a degree of
complexity, but I didn't get that far anyway.

Well, now on to what I think we should look for with our search for an
embedded processor.  And my criteria will apply for COTS or NRAO designed.

The problem is size.  Because the MIB is going into modules, it is natural to
make it as small as possible in all dimensions.  Note the following: (L x W x H)

VLA Dataset = 529mm x 178mm x 36mm
VLBA SIB = 161mm x 140mm x 18mm
AMBSI1 = 160mm x 100mm x 13mm
AMBSI2 = 46mm x 36mm x 16mm

My target was AMBSI2<= MIB <= AMBSI1. Note, this size includes a
complete functional MIB that includes connectors to the Fiber Ethernet and
User Device.  Also it excludes height, which should be kept below 20mm.

The more the embedded processor has in it, the smaller the MIB. So for me the
perfect embedded processor should have:

*Flash memory to hold the RTOS and application
*Enough Static RAM to store data for device and Ethernet.
*Ethernet MII interface.
*A micro to micro communications method such as Dual Port RAM
*A SPI Interface.
*Large external address/data bus 
*Two UARTS.
*Small Package.
*Single voltage supply +3.3V. Can live with two, usually +2.5V for the core.

Nice to have and rather standard for most embedded processors anyway:

JTAG
Watchdog Timer
Timers and/or Real time Clock.
DMA.
Simple chip select logic.
Built-in Floating Point Co-Proccesor

Really nice to have, but could be added externally:

A/D, 8 channels, +/- 10V, 12 or more bits of resolution.
CAN Interface.

Now, I know that I'm wishing for the moon here.  However, for me the EC-1
handed to me most of what I was looking for.  So I want to look for something
that has what the EC-1 offered as well as more.

Now, what criteria have I missed?

Finally, let the hunt begin.  Please provide urls, etc. for your discoveries.

-wayne-