Multiple firewire cameras bandwidth calculation

[sikee]

Hi, all

I saw the table of the maximum packet size based on the camera speed:

Camera Speed	Maximum cumulative packet size
100 Mbps	1024 bytes
200 Mbps	2048 bytes
400 Mbps	4096 bytes
800 Mbps*	8192 bytes

I'm not clear with the calculation. If the camera speed is 100Mbps and the bus is divided into 125um cycles, one cycle is supposed to transfer 125um * 100Mbps = 1562 bytes data. Why the maximum packet size is limited to 1024 bytes? Does it mean the rest are occupied by other tasks, not only for data transfer? If so, the real bandwidth for data transfer is only about 70% bus and it's a great limit to my setup, 'coz I'm trying to plug 6 cameras in one PC with resolution 1624*1236 and frame rate 5fps set. 

Thanks,

Olivia

[BlueCheese]

Yes, only a certain around of the bandwidth on the bus can be reserved for he isochronous transfers that FireWire IIDC DCAM cameras use.

Another solution would be to consider adding a second FireWire card, since the bandwidth is limited per bus. You could also consider moving to a newer standard like GigE Vision or USB3 Vision, as the standards are a bit more flexible about bandwidth usage and also these have basically replaced FireWire in the machine vision market.

[sikee]

OK, I'm clear now. Thank you very much!