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DS90UB954-Q1: Physical meaning of values in CSI-2 timing registers

Part Number: DS90UB954-Q1


Hi,

I would like to understand the physical meaning (time unit) of the values in CSI-2 timing registers.

For instance, when our Deserializer operates at 800 Mbps, the read-out value of the automatically-set CSI0_THS_PREP[6:0] is:

0x06

On the other hand, according to Section 7.4.21 of DS90UB954-Q1 Datasheet, the value "recommended for 400 Mbps operation" of the lower 7 bits of the same register is:

0x03


According to the D-PHY standard (1.2), the valid range for T_HS-PREPARE should be something like:

[min 45ns - max 92.5ns] for 800 Mbps line-rate
[min 50ns - max 100ns] for 400 Mbps line-rate


My question:

How should I interpret those CSI-2 timing register values (0x06 and 0x03), so that I know for sure that the respective Deserializer CSI-2 timing settings (for 800 and 400 Mbps line-rate) comply with the D-PHY standard?

Specifically, can the time unit for those values be calculated as (8000 / lineRate) [ns] ?

e.g.
lineRate = 800 => Time unit = 8000/800 = 10 [ns]
and
lineRate = 400 => Time unit = 8000/400 = 20 [ns] ?

Thanks & best regards

  • Hi Zhe,

    Thanks for your question, let me look into this today and get back to you.

    Best,

    Thomas

  • Zhe,

    There is no simple calculation for deriving each individual CTS parameter from the reg settings, and some of the trim settings are also non-linear in adjustment. So we can't support this request and outside of 400Mbps/lane operation, the timing parameters are all configured automatically by the part and should not be adjusted by the customer. The CSI-2 output has been pre-configured to meet CTS compliance for all specified rates, which means all these parameters will fall within the allowable min/max range that the spec allows (also reflected in the datasheet AC electrical parameters. That is al that we can guarantee and provide. 

    Best Regards,

    Casey