As mentioned earlier, the problem seems to be due to the limitations from host controller.
The video bandwidth for 800*600 @ 10fps can be around 9.1 MBps (considering 2 bytes per pixel)
means 8k and 250us , open 3 cameras successfully!
>> This means that the isochronous endpoint bandwidth is 32.7 MBps for single camera. This can support the video bandwidth and also the host controller is can support 3 cameras with the same bandwidth. In addition to this as the video bandwidth is less than the isochronous endpoint bandwidth i.e. the reason we do not see CyU3PDmaMultiChannelCommitBuffer Fail status = 71. When the USB host doesn't consume the data in the DMA buffers (filled by the sensor) of FX3, there can be DMA overflow condition which leads to CyU3PDmaMultiChannelCommitBuffer failure
means 8k and 125us, open 3 cameras will "show no space left"
>> This means that the isochronous endpoint bandwidth is 65.5 MBps for single camera
When the bandwidth is reduced the host controller supports 3 cameras but for streaming 1200*1200 more bandwidth will be required and it seems that the USB host controller is not able to allot the bandwidth for 3 camera