Alkeria NECTA Series - Preserve Rates; Connecting Multiple Devices to the same Host; Packet Size for Bulk Endpoint

8. Capturing Images 103
where W is the overall size of the sensor (number of pixels in a row) and f
SEN SOR
is 100 MHz.
In other words, the above formula states that the number of bytes sent per micro-frame is the size in
bytes of each frame multiplied by the image rate and divided by 8000 (number of micro-frames per sec-
ond).
The value of I
B
+ CD
B
should be increased by 0.4 % due to communication packet headers overhead.
8.9.5 Packet size for bulk endpoint
Similarly to the bandwidth limit (Section 8.9.3), the packet size represents the average data produced by
the camera every 125 µs. The calculation is performed in the same manner as the isochronous endpoint,
but it is not possible to reserve such bandwidth due to the bulk transfer very nature.
8.9.6 Connecting multiple devices to the same host
When multiple devices are connected to the same host controller, the sum of the bandwidth used by all
the devices must not exceed the total bandwidth available on the host (48 KiB max per micro-frame).
The bandwidth limit control is the right tool that can be used to dene the bandwidth to be reserved to
a single device.
Note
A small part of the USB 3.2 Gen 1x1 bus bandwidth is reserved for control-
ling the camera: depending on the USB 3.2 Gen 1x1 controller you are us-
ing, adding another NECTA camera to the same controller may generate a
small overhead (3-6%) slightly reducing the total bandwidth available for im-
age transfer.
Warning
When using bulk endpoint, keep in mind that the total bandwidth is shared
by all the devices connected to the host. Bandwidth can not be reserved by a
single device but you can limit it by reducing the packet size properly.
8.9.7 Preserve rates
As mentioned before, NECTA updates the lower line period limit when the current packet size is mod-
ied. This happens either upon direct request (see Code 8.13) or when changing parameters affecting
packet size limits (see Section 8.9.4.1).
Whenever the lower line period limit is updated, NECTA can decrease the current line period value to
that value in order to guarantee the maximum available acquisition speed, or the current line period
value can be preserved.
This behavior is controlled by the PreserveRates property. When true, NECTA keeps the previously