What is the limit on simultaneous active USB transactions?

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What is the limit on simultaneous active USB transactions?

Unread postby VittGam » Fri Apr 22, 2016 12:33 pm

Hello,

I think I'm going to buy a C2 soon :D But I need to know one thing before.

How many simultaneous active USB transactions does the S905 support?

For example, the Raspberry Pi supports 8, and that is too few for me.

By the way, I'm talking about USB 2.0 High-Speed devices. Full-Speed devices, if any, will be connected to a Belkin F5U234 hub which is Multi-TT, so no problem with that.

Best,
Vittorio
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Re: What is the limit on simultaneous active USB transaction

Unread postby crashoverride » Fri Apr 22, 2016 12:44 pm

The product page is here:
http://www.hardkernel.com/main/products/prdt_info.php?g_code=G145457216438&tab_idx=2
It indicates the built in hub is "GENESYS LOGIC GL852G"
http://www.genesyslogic.com/en/product_view.php?show=22
GL852G is Genesys Logic’s premium 4-port Hub solution which fully complies with Universal Serial Bus Specification Revision 2.0. GL852G implements multiple TT* (Note1) architecture that provide dedicated TT* to each downstream (DS) ports, which guarantee Full-Speed(FS) data passing bandwidth when multiple FS device perform heavy loading operations.


The C2 also has a USB OTG port that has no hub allowing you connect a hub with the TT capabilities you require.
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Re: What is the limit on simultaneous active USB transaction

Unread postby VittGam » Fri Apr 22, 2016 1:13 pm

Thank you for your reply, but the TT only applies to Full-Speed devices and I already knew that it was not going to be a problem. Furthermore the included Genesys Logic hub is also Multi-TT, so there really is no problem with Full-Speed devices, fortunately. :D

What I'd like to know is the number of possible simultaneously active USB transactions, which is not a parameter of the hub but of the host controller that's inside the S905. It is not the maximum number of devices one can connect to the USB bus; but it's the maximum number of active transactions that there can be in a single moment behind a single root host controller. So there should be one number for the OTG port, and another number that's shared by all of the Host ports.

By the way, are the OTG and the Host ports still handled by the same dwc_otg driver, as in the S805-based C1?
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Re: What is the limit on simultaneous active USB transaction

Unread postby crashoverride » Fri Apr 22, 2016 1:19 pm

The driver appears to be the same as in the C1. However, the issues seen on C1 USB have so far not been reported for C2. I am not sure whether there was driver change, dwc IP block update, or it just works better with a faster processor.

The datasheet for the S905 has not been released yet so many hardware specifications are currently unknown. The limitation faced by the RPI is likely due to their custom USB driver which the C2 does not use.
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Re: What is the limit on simultaneous active USB transaction

Unread postby odroid » Fri Apr 22, 2016 1:21 pm

Their document says, "Supports up to 16 bidirectional endpoints, including control endpoint 0."
But there is no information how many endpoints can run in parallel.

Which device do you want to connect to C2?
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Re: What is the limit on simultaneous active USB transaction

Unread postby VittGam » Fri Apr 22, 2016 2:08 pm

Thank you for your replies! I need to attach many different devices, and I'm hitting the transaction limit on a Raspberry Pi now (the limit for all models of Pi is 8).

Does it say how many host channels there are, per controller? That number should be equal to the number of supported simultaneous active USB transactions.

If the C2 turns out to have 16 + 16 channels, so 16 per controller, then it would be really wonderful! :lol:

crashoverride wrote:The driver appears to be the same as in the C1. However, the issues seen on C1 USB have so far not been reported for C2. I am not sure whether there was driver change, dwc IP block update, or it just works better with a faster processor.

The datasheet for the S905 has not been released yet so many hardware specifications are currently unknown. The limitation faced by the RPI is likely due to their custom USB driver which the C2 does not use.


It seems that there is no dwc_otg anymore in the C2 kernel tree. It should use the upstream dwc2 driver. But I just gave a very quick look. :lol:
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Re: What is the limit on simultaneous active USB transaction

Unread postby odroid » Fri Apr 22, 2016 2:15 pm

There is no such information. It is very hard to confirm before trying the same devices.
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Re: What is the limit on simultaneous active USB transaction

Unread postby VittGam » Fri Apr 22, 2016 2:21 pm

Strange, the S805 datasheet said that information on page 111, and it was 16 + 16.

Anyway, I'm still going to get the C2 when they'll be in stock again. Even if it doesn't allow for more USB transactions, the C2 is still going to be way better than any model of RPi! :lol:
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Re: What is the limit on simultaneous active USB transaction

Unread postby odroid » Fri Apr 22, 2016 2:26 pm

Ah.. I found that each host and otg controllers have 16 host channels like the C1.
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Re: What is the limit on simultaneous active USB transaction

Unread postby VittGam » Fri Apr 22, 2016 2:33 pm

That's really perfect then. :lol:
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