Integrating XMOS processors with custom PCB board designs

Technical discussions around xCORE processors (e.g. General Purpose (L/G), xCORE-USB, xCORE-Analog, xCORE-XA).
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Bianco
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Re: Integrating XMOS processors with custom PCB board design

Postby Bianco » Wed Jan 22, 2014 9:00 pm

Not sure which part you are referring to, but a fully bonded out xcore tile has four 8-bit ports.
For example the XS1-L8A-64-TQ128.
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segher
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Postby segher » Wed Jan 22, 2014 9:19 pm

Most people who use U devices use the USB. When using
the USB, ports 8A and 8C are not available. If you need
more 8-bit ports you can use an A device, or some dual
core device.

A port clocks out data on the rising edge of its clock. It
clocks in data on the falling edge by default, but you can
change that. You can also invert the clock. And you can
fine-tune the clock edges (by delaying them) if you really
have to.
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MatCat
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Postby MatCat » Wed Jan 22, 2014 10:03 pm

The Dev Board I am working on designing is for the U6A/U8A, XOD02-XOD09 = 8A, not pinned out on FBGA96, XOD26-XOD33 is 8C also not pinned out, XOD36-XOD43 is 8D, also not pinned out.

However XOD49-70 is pinned out but of course they are ALL part of 32A, which of course the entirety of 32A isn't even pinned out on these chips, nor do they have any secondary ports.
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segher
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Postby segher » Wed Jan 22, 2014 10:44 pm

As I tried to explain (and miserably failed it seems), even if
8A and 8C would be pinned out you still couldn't use them
(as ports) while using USB. Using the pins for 32A instead
is more useful for most people.

You can use the 20 port 32A pins for slowish 1-bit outputs,
and/or for wider busses, and/or for xlinks. Less convenient
than "real" 8-bit ports for sure, but still more useful than pins
you cannot use at all!
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segher
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Postby segher » Wed Jan 22, 2014 11:03 pm

About 8D... 8D7 _is_ pinned out, it has a dual function as
the WAKE pin. Why the other seven pins of 8D are not pinned
out on any of the U or A devices, I have no idea. I agree it
would seem useful. Any theories?
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MatCat
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Postby MatCat » Thu Jan 23, 2014 12:16 am

For sure you can use them, but it seems to me that they would be better served to put some 4 bit and 8 bit wide hardware supported ports on the 32A port.

It seems to me the hardware port capabilities of the chip are one of the features that give it the edge in a potential use, but the way it's setup it doesn't take the best advantage of it on that particular chip, I haven't looked at the full pinouts of every xcore chip, but I do know I don't have a PCB fab in my budget that is capable of the lower pitched BGA for prototyping!

At better look it seems the L8A has quite a bit better pin out (looking at TQFP), I don't see why 2 8 bit ports should be knocked out of commission for USB?

Anyway just my view on it thus-far, my goal in wanting to get and play with the StartKit was to evaluate the chipset for potential use in future products, and see what it can do, ultimately I like the idea, I liked it enough to design a dev board to make a few to experiment with other xcore chips, but these are the few things I see that could use some improvement to make the chips more versatile.
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segher
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Postby segher » Thu Jan 23, 2014 12:37 am

MatCat wrote:For sure you can use them, but it seems to me that they would be better served to put some 4 bit and 8 bit wide hardware supported ports on the 32A port.
That would require a new silicon spin.
It seems to me the hardware port capabilities of the chip are one of the features that give it the edge in a potential use, but the way it's setup it doesn't take the best advantage of it on that particular chip, I haven't looked at the full pinouts of every xcore chip, but I do know I don't have a PCB fab in my budget that is capable of the lower pitched BGA for prototyping!
Maybe someone can make breakout boards, similar to the
L1 DIP thing. Most people should have no problems with these
BGAs (everything else is a BGA as well these days), and flat pack
or similar requires a bigger package (and it already isn't small).
But yeah, harder to solder by hand, sure.
At better look it seems the L8A has quite a bit better pin out (looking at TQFP), I don't see why 2 8 bit ports should be knocked out of commission for USB?
Data in and out from the PHY. There are also some 1-bit
ports used. L series needs *all four* 8-bit ports for USB, btw. ;-)
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MatCat
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Postby MatCat » Thu Jan 23, 2014 5:38 pm

segher wrote: That would require a new silicon spin.
Yep it would.
segher wrote: Maybe someone can make breakout boards, similar to the
L1 DIP thing. Most people should have no problems with these
BGAs (everything else is a BGA as well these days), and flat pack
or similar requires a bigger package (and it already isn't small).
But yeah, harder to solder by hand, sure.
It's not a matter of soldering, I have a reflow oven and all the tools to do BGA, it's a matter of getting a PCB company that can do fine bitched BGA's, all the companies I use are limited to 6 to 8 mil traces, and 2 to 4 layers, you just can't do a higher density BGA on those limits. Really it limits those chips to larger companies or those with the money that can afford to do PCBs at a place that can do such tight tolerances.
segher wrote: Data in and out from the PHY. There are also some 1-bit
ports used. L series needs *all four* 8-bit ports for USB, btw. ;-)
That is just silly really, I think a better solution could be find to not take out so many resources for something that essentially only needs 2 data lines externally. Is there USB on the L series or are you just saying if one wanted to do USB functionality in software?
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segher
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Postby segher » Thu Jan 23, 2014 6:03 pm

MatCat wrote:It's not a matter of soldering, I have a reflow oven and all the tools to do BGA, it's a matter of getting a PCB company that can do fine bitched BGA's, all the companies I use are limited to 6 to 8 mil traces, and 2 to 4 layers, you just can't do a higher density BGA on those limits. Really it limits those chips to larger companies or those with the money that can afford to do PCBs at a place that can do such tight tolerances.
U and A series chips should be easy to integrate on two-layer
boards (the datasheets show examples, looks quite straightforward).
Are you saying 0.8mm ball pitch is too small? That's what, 16
mil space per trace?
That is just silly really, I think a better solution could be find to not take out so many resources for something that essentially only needs 2 data lines externally.
You can add a bunch of resources, or use the ones you already have. More a
question of philosophy than anything else.
Is there USB on the L series or are you just saying if one wanted to do USB functionality in software?
L does not contain a PHY, but it does have everything else.
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mon2
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Postby mon2 » Fri Jan 24, 2014 5:13 am

It's not a matter of soldering, I have a reflow oven and all the tools to do BGA, it's a matter of getting a PCB company that can do fine bitched BGA's, all the companies I use are limited to 6 to 8 mil traces, and 2 to 4 layers, you just can't do a higher density BGA on those limits. Really it limits those chips to larger companies or those with the money that can afford to do PCBs at a place that can do such tight tolerances.
Err..think you mean pitched :) Sorry, spelling police now off.

How low cost are the vendors you are using ? Need to review if the cost savings are really worth it. We have invested years into sourcing from quality vendors and have been to Asia to listen to sales pitches that led to further waste of time and money. One of our suppliers can support up to 58 layers (!!) but of course, at a premium cost but they are the best in China. Seriously.

Try jetpcb.com - we have used them for many years on proto runs. Frank runs their US office and they are pros in this field. However, need to know that their focus is only prototype qty so believe 200 pieces is a max per order but they are fine with even a single PCB order. Some of the largest semiconductor firms (Maxim, Asus and others) use their services - saw this at the Taipei trade show last October. We rate them 10/10 and we are quite picky. If necessary, they are able to support down to 3 mil space / traces. As you may be aware, proto shops use a different method of tooling and testing for small qty. Respectively, if you do kick into any volume then you will be required to invest into a hard tool (often around $400-$700 varying with complexity) with another shop for your design but then the individual PCB costs will drop.

Another vendor you can ask is IBE with website of pcbaaa.com as we spent some time at their booth last October. Had some really high quality PCBs on display. They want to compete with other proto shops so may be worth trying. We have not used their services but came to mind.

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