TDES954: I2C mapping for CSI-2 Sync and STP mode

Hello Austin,

If you can talk to each device through a local I2C connection, then it seems all devices are powered-up properly. 

Is your main problem that you can't communicate with a remote device through the V3Link channel?

For example, are you havingg trouble sending an I2C command from SoC -> TDES954 -> TSER953?

Are you able to confirm if you have LOCK established on the TDES954 device? You can check this by going to the TDES954 and reading register 0x4D. Please note that this is an RX-Port specific register and you need to select an RX Port to read from first in register 0x4C.

Are you also able to provide a register dump of the TDES954 and TSER953 devices?

Best,

Justin Phan

Thats correct we cant get anything from the V3 link just yet. 

Here is the register dump

Hi Austin,

From the register map, LOCK is not set.

We expect 954 reg 0x4D = 0x03 on a successful link.

I see that 954 reg 0x58 = 0xDE, which means the BC is the correct frequency. Can you share the 953 register dump? And can you share the resistors used on the MODE pin of the 953 device? I want to make sure that the serializer is in the same MODE setting as the deserializer.

Also, this is a small note. Can you make sure that 954 reg 0x58 = 0x5E?

You don't want to set bits 7 and 6 at the same time. You only want to set one of them at a time, with the most common use case setting the I2C_PASS_THROUGH bit only.

This is not a direct reason for the I2C issue. You mainly need to get LOCK established first.

Best,

Justin Phan

We did just change the 954 register as both 7 and 6 were set high. 

Here is the SER dump

Since I want CSI mode would having a crystal on the serializer make it so it wont work? I can depop it, I just realized I had a crystal on both the SER and DES.

Hello Austin,

It doesn't matter if you put a crystal on the serializer in SYNC mode. In SYNC mode, the serializer will just ignore the local crystal and use the BC provided by the DES as its REFCLK.

From these register dumps, I see that the 953 and 954 are in matching correct MODEs, but the LOCK is still not enabled. In that case, there are a couple possible causes:

1. Maybe there is something on the V3Link channel that is causing issues. Can you share the connections you made from the IC to the connector on both the 953 and 954 boards?
   1. I mainly want to check if the capacitors are correct and if there is anything along the high-speed path that is suspicious.
   2. If you can send me the schematics for the 953 and 954 boards, that would be faster for me to check.
2. Have you measured or simulated Insertion Loss and Return Loss on the high-speed channel?
   1. Maybe it's possible that the high-speed channel is lossy, which is causing the 953 and 954 to not be able to detect each other.
   2. Also, what cable are you using to connect the 953 and 954 boards together? What length and cable type?

Best,

Justin Phan

is there somewhere I can send this confidentially? 

You can email it to my work email:

j-phan1@ti.com

This is the DES without anything connected to the V3 link

When I connect the Serializer it just looks like complete trash, basically noise. 

One thing I thought as well was that since were using a STP do we have to change the i2c setting so that we use STP instead of Coax? It says something about strapping resistors can be used to do this automatically on the MODE pin but that didnt make sense to me since that dictates what mode the DES is going to be in. 

Hi Austin,

What are you trying to measure here?

The SerDes devices are bidirectional. Meaning that the serializer is outputting a 4Gbps (2GHz) signal and the deserializer is outputting a 50Mbps (25MHz - 50MHz) signal. The SER and DES devices also have 50-Ohms terminations at each receive port as well. If you power-up the deserializer and probe the RIN+/- pins with a differential probe that has 100-Ohms termination, then I expect that you should see a fluctuating signal, with a max frequency of about 50MHz.

Also note that the signals are not clock signals. They are fluctuating, since they all contain data.

There is no software setting to switch betwen STP or COAX mode. All that is required is a hardware change. You need to change the AC coupling capacitor on the RIN-/DOUT- trace to 15nF and add a 50-Ohms termination resistor at the RIN-/DOUT- trace.

If you want to test COAX in your current hardware, you need to replace C2 with a 15nF capacitor. And find a way to terminate the RIN- line with a 50-Ohms resistor to GND.

Best,

Justin Phan

I was measuring the differential voltage at the Deserializer with nothing connected to make sure something was happening at least.

the TDES954 data sheet says PORT_CONFIG address 0X6D details that you can switch between COAX_MODE and STP mode and the default value is made by a strap condition of mode pin is this not correct then?

This what it looks like if I measure with differential probes at the AC coupling caps. my scope only goes up to 1GHz so I know I cant see the message properly by any means but Im assuming this is what youre meaning by the bidirectional communication?

Hello Austin,

Austin Ensign said:

This is the DES without anything connected to the V3 link

This is an image of what I kind of expect. If you turn on the measure frequency tool in your scope, it should read a fluctuating frequency that occasionally shows 50MHz. But it fluctuates since this is a data signal and not a clock signal.

Austin Ensign said:

the TDES954 data sheet says PORT_CONFIG address 0X6D details that you can switch between COAX_MODE and STP mode and the default value is made by a strap condition of mode pin is this not correct then?

This setting is not necessary to change.

Austin Ensign said:

This what it looks like if I measure with differential probes at the AC coupling caps. my scope only goes up to 1GHz so I know I cant see the message properly by any means but Im assuming this is what youre meaning by the bidirectional communication?

Make sure to only power one device, either the Ser or the Des, at a time. Otherwise, you will see 2 signals on top of each other.

Best,

Justin Phan