DS90UB953-Q1: Bandwidth Calculation Clarification

David Shumate

Part Number: DS90UB953-Q1

Hi Team,

I watched the CSI bandwith calculation video below and need your help clarifying incorporation of overhead into the calculation so I can understand the limits of our seralizers better.

Video: https://training.ti.com/csi-2-aggregation-breakdown?context=1134310-1139225-1148220

The input bandwidth section has the following calculations:

I have an example that is very close to the 3.328Gbps BW limit of the 953 so I need help understanding if I'm calculating everything right. Here is my calc sheet:

Using a 4.16Gbps Link and a 953 with bandwidth capabilities of 3.328Gbps it looks like this will not work unless I dial the FPS down to 58 fps instead of 60.

Am I understanding this correctly?

My main question is do I still need to add an additional 10%-25% overhead on top of this like we do with the FPD calculator or does this somehow get accounted for in the calculation?

- If I do still need to add an additional overhead is just using 10% (or maybe less) for the CSI overhead enough as I've already accounted for blanking in the above calculation?

Thanks for the help!

David

over 3 years ago

0 Shruti More over 3 years ago

TI__Expert 6345 points

Hello David,

Yes, your understanding is correct.

Yes, you do still need to add an additional overhead (on top of the blanking overhead) to account for the CSI-2 protocol overhead.

Best Regards,

Shruti

0 David Shumate over 3 years ago in reply to Shruti More

TI__Expert 7905 points

Hi Shruti,

Thanks very much for taking a look. Since we are so close, could you comment on what the minimum acceptable overhead multiplier would be?

Looks like when I include 10% overhead in the calculation that brings me down to 53 fps to stay below 3.328Gbps limit:

I'm not sure if 10% is either too conservative or too aggressive in this case though.

Best,

David

0 Shruti More over 3 years ago in reply to David Shumate

TI__Expert 6345 points

Hello David,

I suggest you consult the image sensor datasheet or reach out to the image sensor vendor to check how much CSI-2 overhead you should account for at the CSI-2 outputs of the imager and the frame rate.

Here is a similar E2E thread that discusses estimating overhead in BW calculations: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/790487/ds90ub953-q1evm-required-data-bandwidth

Best Regards,

Shruti

0 Christian Euler over 3 years ago in reply to David Shumate

Genius 4135 points

Hi David,

I am confused now - I was assuming the protocol overhead is already included in the reduction from 4.16 Gbps to 832Mbps per lane - so do we need to add another overhead here?

0 David Shumate over 3 years ago in reply to Christian Euler

TI__Expert 7905 points

Christian,

The original recommendation for overhead was 10-25% to cover both blanking and CSI overhead.

Pulling from the thread that Shruti linked the 25% recommendation from sally came from 15% being associated with blanking and 10% associated with CSI overhead

Since we have accounted for blanking now in our calculation we can remove the 15% overhead estimate associated with blanking but the 10% CSI overhead will still be there. Please note that the 10% CSI overhead is an estimate the actual CSI overhead number should come from the imager supplier as Shruti mentioned above.

0 Shruti More over 3 years ago in reply to David Shumate

TI__Expert 6345 points

Hello David,

Thank you for explaining.

Best,

Shruti

0 Christian Euler over 3 years ago in reply to Shruti More

Genius 4135 points

Hi,

ok - understood.

Checked this w/ OVT:

- We have a resolution of 2592 x (1944+184) = 2592 x 2128

- We have to assume 15% MIPI Overhead

Thus we end up w/ ~960 Mbps per lane what is more than the serializer supports.

Calculating back, I end up w/ ~52Hz framerate.

Imager Cols	2592
Imager Rows	1944
Blanking Lines	184
Bit Per Pixel	10
Frames Per Second	60	Hz
Line Time	7,83	µs
Bits per Line	25920
Req. BW	3,31	Gbps
MIPI Overhead	15%
Total BW	3,81	Gbps
# Lanes	4
Bw / Lane (Imager)	951,47	Mbps
BW / Lane (Serializer)	832	Mbps

0 Shruti More over 3 years ago in reply to Christian Euler

TI__Expert 6345 points

Hello Christian,

Thank you sharing the video parameters. It looks like the 953 will not be able to handle this imager bandwidth. I will reach out to David Shumate and discuss other options for serializer that can handle your imager's video parameters.

Best Regards,

Shruti

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DS90UB953-Q1: Bandwidth Calculation Clarification