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DS90UB954-Q1: Question for CSI-2 setting

Expert 4525 points

Replies: 7

Views: 108

Part Number: DS90UB954-Q1

Hi Team,

My customer asked CSI-2 setting for below specific case.

Could you check if below settings are reasonable to have sufficient bandwidth?

<<  System requirement >>

1. configuration : CMOS sensor + 953 + 954 (single 953 is connected)

2. streaming data : 1920x1080x60fps, 12bit/pixel (Raw12bit)

     --> 1.64Gbps with Blanking rate =1.1

3. max 1.5Gbps for ISP lane

<< DS90UB954 configuration >>

1. For FPDLINK setup for non-synchronous CSI-2 mode

set FPD3_MODE = "00",

REFCLK = 25MHz(from xtal oscillator)

2. For CSI-2 setup

From Table 13, to set CSI frequency less than 1.5Gbps with REFCLK=25MHz,

(1) CSI_PLL_CTL[1:0] has to be set as "00"

(2) IND_ACC_CTL[5:2] =  "0111"

(3) IND_ACC_ADDR = 0x08

(4) IND_ACC_DATA[7:6] = "11" (csi pll divider setting = 52)

(5) CSI_LANE_COUNT = "10" (2 lane)

With this setting, I expect 954 has 1.3Gbps x 2 lane capability.

Best regards,

Nobuo

  • Hi Nobuo,

     Thank you for the detailed setup description.  Exploring this issue and will send an update tomorrow.

    Sincerely,
    Bryan Kahler

  • In reply to Bryan Kahler:

    Hi Nobuo,

    Still looking into this.  Will have an update with respect to the calculations tomorrow.  Is the customer currently experiencing issues with these settings?

    Sincerely,
    Bryan Kahler

  • In reply to Bryan Kahler:

    Hi Nobuo,

    10% overhead (as blanking, above) may be a bit optimistic.  Recalculating with a more conservative 25% for total overhead gives ~ a 2 Gbps max throughput of the serialized data rate, which is still well below the NET CSI-2 video bandwidth per RX port given in Table 13 of the 954 datasheet.

    Setting CSI_PLL_CTL to 00 is good, but with a 25 MHz XTAL, will exceed your CSI-2 TX Data Rate per Lane limitation of 1.5 Gbps (at 1600 Mbps).

    Please change your XTAL to 23 MHz for a CSI-2 TX Data rate per lane of 1472 Mbps.  With 2 CSI-2 lanes being utilized, this is ~3 Gbps of throughput, more than the ~2 Gbps required (with overhead) in the calculation above.

    Please let me know if you run into any issues!

    Sincerely,
    Bryan Kahler

  • In reply to Bryan Kahler:

    H Bryan,

    Thanks for the answer.

    Customer wants to use 25MHz Xtal.

    Can you check if below E2E thread works to configure 1.3Gbps per lane?

    DS90UB954-Q1: CSI-2 Bandwidth Options:

    https://e2e.ti.com/support/interface/f/138/t/777100?tisearch=e2e-sitesearch&keymatch=DS90UB954-Q1%25252525252525252520AND%25252525252525252520csi-2

    Best regards,

  • In reply to NOBUO FUJIHARA:

    Hi Nobuo,

    1.472 Gbps ~= 1.5 Gpbs with a little headroom so you don't violate spec. 

    Also, you have the added benefit of working within the settings on the Datasheet.  If you're using undocumented features, you will need to perform your own validation of those features.

    Is the customer currently experiencing issues with the sequence you have proposed?

    Sincerely,
    Bryan Kahler

  • In reply to Bryan Kahler:

    Hi Nobuo,

    Haven't heard from you in a while - hopefully no news is good news and the issue is now resolved.  If so, please mark the issue as resolved. 

    If not, please let us know.

    Sincerely,
    Bryan Kahler

  • In reply to Bryan Kahler:

    Hi Bryan,

    Sorry for delayed response, customer agreed to change Xtal to 23MHz.

    Best regards,