Custom Board XLINKS

[rp181]

Yes, I do have a logic, but I also have a 100mhz 4ch oscilloscope. The plugin would be great!
Did you get a chance to verify the wiring?

[Bianco]

I haven't looked at it in depth yet.
I'll do that tomorrow.

[rp181]

Anybody have any ideas? Have no idea what to try.

[Bianco]

Right... i finally took the time to take a better look at the schematics.

I found a bug with the XMOS Links: when two boards are connected to eachother the outputs are tied to the outputs and the inputs are tied to the inputs.

See following:

Code: Select all

Node 0 (SKT_BOT)           Node 1 (SKT_TOP)

Net     Function           Net     Function
OXU1    LD1out     <-->    IXU1    LB1out
OXU0    LD0out     <-->    IXU0    LB0out
OXD0    LD0in      <-->    IXD0    LB0in
OXD1    LD1in      <-->    IXD1    LB1in

You have used the XK-1A as a reference design and they use the same net name convention for the same pin numbers on the XTAG2 connectors. For example pin 6 on JTAGOUT is called OXU1 and pin 6 on JTAGIN is called IXU1. OXU1 on the XK-1A is connected to LD1in and IXU1 is connected to LC1out.
The mapping from these netnames to pins is done in the table below the connectors in the schematic.
This is rather confusing. U stands for Up and D for down. The naming reflects the real situation in a multiboard setup when you send data from node 0 to the last node: all lines it traverses are called up lines and communication from the last node to node 0 will traverse all down lines. So it does not reflect input or output.

[rp181]

Wow, that is confusing. When I was tracing the connections, this is what I found:
XK-1A:
C1in-D1out
C0in-D0out
C0out-D0in
C1out-D1in
My board:
B1in-D1out
B0in-D0out
B0out-D0in
B1out-D1in

You say net OXU1 is D1out. I have it connected to X0D64, which on the datasheet is X0D1in. Am I missing something?
Keep in mind that the A and B links are reversed from the C and D links when going up in pin number. A and B go out,out,in,in. C and D goes in,in,out,out.

[Bianco]

I'm absolutely positive. Since your multiboard JTAG is functional we can take that as a reference for the connections of the xmos links between the two boards. Lets take a look at one of them:

Pin P35 of connector SKT(TOP) will connect to P46 on connector SKT(BOTTOM). We know this for sure since it is one pin above TMS and three pins below TRST_N.

Pin P35 on SKT(TOP) has netname IXU1, connects to pin X0D16 and has the functionality of X0LB1out.
Pin P46 on SKT(BOTTOM) has netname OXU1, connects to pin X0D64 and has the functionality of X0LD1out. So.. X0LB1out is connected to X0LD1out on the other board!

I have it connected to X0D64, which on the datasheet is X0D1in. Am I missing something?

What datasheet are you using? In mine X0D64 is X0LD1out.

[rp181]

Well, there's the problem. My datasheet is wrong. This is the one I have been using for ages:
http://www.xmos.com/system/files/xs1-l1-128tqfp-ds.pdf

[Bianco]

Ouch...

[rp181]

Yeah, 6 layer boards aren't the cheapest either.

I emailed XMOS and asked them to take this datasheet down. This is also the one that comes up when googling "xs1-l1-128".

[rp181]

What is the difference between the XS1-L01A and the XS1-l1?