Daisy chain interconnection

[amvasil]

Hello!

I'm trying to connect two Red Pitayas via daisy chain connector. I couldn't find any avaliable docs so I'm trying to figure something out experimentally.

Daisy chain connector of Pitaya 1 (lower) is connected to other Pitaya connector (higher) by SATA II cable. I suppose first connector is Tx and second is Rx because other way it doesn't work at all. So, I type

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monitor 0x40500000 0x3

on both Pitayas (ssh) to enable transmitters and receivers. After that, I set up transmitter:

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monitor 0x40500004 0x12340002

to write 1234 to port, and then in receiver Pitaya:

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monitor 0x4050000C

And I get

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0x00002341

First 2 bytes have to contain somehow processed input (not zero, as stated in register map description file), and second 2 bytes contain raw input. By the way, they usually seem to be input barrel shifted 1 byte left. Also it strangely reacts to unplugging and plugging back cable: after some manipulations I got result like 0x00001234 (correct).

Is there any way to get it work correctly and more reliable?

Alex.

[Nils Roos]

Hi,
I haven't tried it myself yet, but there are some comments in the verilog code to the effect that the receiver needs to be trained before communication can take place.
During training (which has to be done each time the physical connection is made) the receiver waits for a specific bit pattern (0x00ff) and synchronizes on that.

So, set the receiver to training mode by writing 1 to 0x40500008, then start training on the transmitter by setting mode 3 - or maybe in reverse order, I'm not quite sure about that. After synchronisation is established, data transmission should work without unexpected bit-shifting. You can verify the success of receiver training by reading 0x40500008, bit 4 is set when training succeeded.