High speed USB devices

On 04/05/2011 08:44 PM, Mikko OH2HVJ wrote:
> Christopher Felton<noemail@now.com>  writes:
>
>> In most cases we have seen the bottle-necks on the PC side.  The FX2
>> with the default 512 EP FIFO was sufficient to get to ~30MB/sec.  The
>> buffering and threading on the PC side has to be handled carefully.
>> It will depend on the drivers you are using on the PC, how often you
>> get the data (poll or block), and how many threads.
>
> Fortunately in this application we'll have almost full control of the PC.
> The first version will be using the common consumer-grade OS, but later
> on there will be a custom Linux box on the other end of the USB.
>
> We'll have a buffer for a few frames, so matching the sensor timing with
> USB traffic is 'easy'.

In my experience, with a FPGA + USB 2.0 PHY and Linux host with a decent 
driver it is possible to get almost theoretical throughput (minus normal 
protocol overhead).

In my case, saving the data to a hard drive was the bottleneck, but that 
was a few years ago when drives were a lot slower.

Mikko OH2HVJ skrev 2011-04-03 20:26:
> Hi,
>
> I'm building a custom USB-camera. There will be an FPGA chip doing some simple
> data handling for the sensor data and after that the image needs to be
> transmitted to a PC or an embedded Linux computer.
>
> Estimated raw data rate is almost 30 megabytes per second without any
> compression. Basically a single endpoint is enough for the task.
>
> What are the available chips in addition to Cypress FX2, NXP ISP1581 ?
>
> And how much compression will I be needing, i.e. what is the best performance
> available ?
>

If you are going to connect it to an embedded Linux,
why not put the FPGA inside the Linux box, and run a faster interface?

The AT91SAM9M10 has a a dual bus structure, so you
can put the FPGA on the secondary bus, and DDR2 on the primary
bus and move data using high speed DMA.
DDR2 supports 533 MB/s peak so you will be using < 10 % of the bandwidth.

What is the Linux box (or PC) going to do?


Best Regards
Ulf Samuelsson

On Apr 12, 3:19=A0pm, Ulf Samuelsson <u...@a-t-m-e-l.com> wrote:
> Mikko OH2HVJ skrev 2011-04-03 20:26:
>
> > Hi,
>
> > I'm building a custom USB-camera. There will be an FPGA chip doing some=
 simple
> > data handling for the sensor data and after that the image needs to be
> > transmitted to a PC or an embedded Linux computer.
>
> > Estimated raw data rate is almost 30 megabytes per second without any
> > compression. Basically a single endpoint is enough for the task.
>
> > What are the available chips in addition to Cypress FX2, NXP ISP1581 ?
>
> > And how much compression will I be needing, i.e. what is the best perfo=
rmance
> > available ?
>
> If you are going to connect it to an embedded Linux,
> why not put the FPGA inside the Linux box, and run a faster interface?

Actually, he would need both.  Parallel to Serial on the device side
and Serial to Parallel on the Linux side.

> What is the Linux box (or PC) going to do?

Compression?

Ulf Samuelsson <ulf@a-t-m-e-l.com> writes:
> If you are going to connect it to an embedded Linux,
> why not put the FPGA inside the Linux box, and run a faster interface?

The camera has to be small&light with about 1.5m very flexible cable. And 
we'd like to start the project using a PC and later move to the custom Linux box.

> What is the Linux box (or PC) going to do?

Video compression, simple UI and networking. The first one requiring some DSP power or
a codec core. 

-- 
Mikko

On Apr 13, 11:08=A0am, Mikko OH2HVJ <oh2...@sral.fi> wrote:
> Ulf Samuelsson <u...@a-t-m-e-l.com> writes:
> > If you are going to connect it to an embedded Linux,
> > why not put the FPGA inside the Linux box, and run a faster interface?
>
> The camera has to be small&light with about 1.5m very flexible cable. And
> we'd like to start the project using a PC and later move to the custom Li=
nux box.
>
> > What is the Linux box (or PC) going to do?
>
> Video compression, simple UI and networking. The first one requiring some=
 DSP power or
> a codec core.

I assume you want more than 640x480, than you might need more than
480M to move the raw data.  You might need multiple USB or PCIx.