I have 1 Full Speed (12 Mbps) CDC-ACM type USB device connected directly to a High Speed (EHCI - 480 Mbps) controller on a SoC.
When there is no user-space application opening the CDC-ACM device in linux, I see a pulse which is repeated every 1 ms (SOF). Once an application (example cat) opens the CDC-ACM device, I see a lot of IN tokens (~102) between 2 SOF's from the host and the device NAKs the IN token. We are suspecting the device is busy NAKing that it hampers its operation.
Q1: Is there a way to reduce the number of IN tokens within the 1 ms interval?
Thanks
0_l_0
Related
In our application we are sending ADC data(240 bytes) to host computer through USB at full speed and using Serial application like (teraterm/minicom/Docklet) to validate the data, but we are facing the issue of data loss.
We are not getting where the issue is weather the seral application is not able to handle the incoming data or is there any limitations at controller side operating at USB full speed?
Microcontroller - NRF52840
USB class - CDC ACM
Best regards
Sagar
Suggest you entirely disable (temporarily) the ADC function and only have the microcontroller send a counting sequence to verify the known pattern is transferred without loss to the PC side. If the pattern is detected without loss, then re-enable the ADC function, but still only send the counting sequence and test again. If data is missing, then the problem is most likely the ADC function is causing a timing condition (such as blocking the CPU too long).
I am working on a hardware-embedded software project involving USB protocol. My plan is to use a USB3.0 Hub that clusters many USB2.0 isochronous devices, each requiring around 33 Mbps BW.
Now, I know that USB3 is able to enumerate up to 127 devices [1], what I'd like to know is whether this is true if I connect USB2 devices to the USB3 Hub. Can I, in theory, use the hub with 97 USB2 devices?
Also, could I utilize the entire BW (yes, only around 70% is feasible) of a USB3 port this way? The above figures add up to 5 Gbps*70% = 3.2 Gbps = 97*33Mbps.
Any help is much appreciated.
I believe there is some confusion with your understanding.
USB 3.0 hub contains 2 logical hub partitions.
1 - USB 3.0 hub
2 - USB 2.0 hub
USB 2.0 devices communicate through the USB 2.0 hub data path which has nothing to do with USB 3.0 data path. So the assumption of the bandwidth is incorrect as they are for USB 3.0 devices connected via USB 3.0 data path.
Also USB 2.0 devices will get connected via USB 2.0 lines and NOT USB 3.0 lines.
Another misconception in your question.
The speed which you mentioned i.e. 5 Gbps, that is USB 3.0 link speed.
What that means is that 2 devices over USB 3.0 link can send or receive data at 5 Gbps. Since every hub downstream port is physically a separate link, the link speed will be same for all i.e. 5 Gbps. So its speed between 2 link partners and not end to end speed.
Now when you say End to End data transfer rate, that will depend on your host controller driver architecture, your OS performance, your Hub, etc.
For Isochronous endpoints, the hub will start data transfer on service intervals for each endpoints on each port as per USB spec but you cannot be sure that End to End data transfer rate will be equally divided.
PS - You will get a lot less end to end bandwidth by the way as the link speed for USB 2.0 is 480 Mbps. :)
I have an old hub that sucks, so I converted it to a USB-tripler by soldering all of the input 4 wires to the corresponding wires on the output connectors. I had to do this because modern devices require 2.0 or 2.8 volts on d+, and refuse to charge if d+ is shortened or not connected. It works well charging three devices from a 1a wall adapter.
But if someone accidentally connects this to a PC port, what will happen? Well if there is only one device, it would be detected no problem. But if two devices are wired to the same port, how dangerous is that?
I would prefer the first connected device to be identified in the system, while the second connected devices just get the power.
One of the first steps in USB enumeration is to send a reset signal by driving D+ and D- low. All the devices plugged in will see the reset and think it was intended for them. After the reset they will each think they have address 0 and respond to requests to that address. The result will be multiple devices trying to drive the bus at the same time, for a brief period before the host gives up.
I think it wouldn't damage anything, but you will be causing a short circuit for a few microseconds which is bad.
Is there any USB 3.0 hub or device that multiple USB 2.0 devices can be connected to and still retain the maximum USB 2.0 bandwidth for each device by utilizing the higher bandwidth of USB 3.0?
These devices exist for USB2.0/1.1 interfacing (they are called Multi-TT USB hubs).
Are there any such devices that exist for USB3.0/2.0? What I'm trying to do is connect 3 high-bandwidth USB 2.0 cameras to one USB 3.0 port.
I've been personally trying to find details about this as well. I'm trying to get multiple USB based audio cards to MUX over USB 3.0.
So far the following two URLs are giving me my details:
http://www.via-labs.com/en/products/vl810/index.jsp
http://electronicdesign.com/embedded/what-s-difference-between-usb-20-and-30-hubs
-- 1 --
This is interesting because it shows a block diagram of the VIA VL810 controller chip. Unfortunately, it sure looks like the USB2.0 functions are completely seperate from the USB 3.0 sections. This leads me to believe that, at least this chip, and HUBs that use it, can not multiplex USB2.0 transfers over USB3.0.
-- 2 --
This site spends a lot of time talking about how the HUBs are suppose to work. It takes the time to explain that the USB3.0 bus is separate from the USB2.0 bus:
Within the hub, only the port power control logic is shared between the USB 3.0 path and the USB 2.0 path, since there is only one 5-V power path in either USB 2.0 or USB 3.0.
This leads me to assume that most if not all current USB 3.0 HUBs can't multiplex.
You comment about Multi-TT Hubs being available for USB 2.0/1.1 gives me hope that some time in the (near?) future we'll have the same ability with USB3.0/2.0.
I am developing an application that sends data per UDP using AsyncUDPSocket class to another client on Mac and Windows. It is very important that packets arrive instantly.
The problem is that every approx. 1000 packets I get a delay for about 2 seconds when receiving Packets. A delay of 100-200 ms would be OK, but 2 seconds produce bad user experience.
I have the UDP communication in a separate Thread, so it is little affected by user interaction with UI and such. I have already tried sending Packets faster, slower, different Packet sizes: the delay stays there. Tried using TCP instead of UDP - same result :(
It does not seem to happen on Windows Cliets.
Maybe there is some system buffer in MacOS that needs to be flushed every time it hast N packets or N bytes of data???
Has anyone an idea how can I prevent the delay from happening?
There are a lot of things that can slow down a network program temporarily, it's hard to know where to start. Have you tried this on multiple networks? Both wireless and ethernet networks? What kind of switch do you have? Does this happen on different OS X computers, or just on one? Can you reproduce the delay with a simpler command line program? Are you using garbage collection? (Grasping at straws here...)
Just out of curiosity, I tested the roundtrip time on UDP echo packets sent from my Mac to another computer on the same LAN. Out of over 60,000 UDP packets with a 1,000 byte payload, none of them took longer than 32 ms, the mean round trip was 0.6 ms, and the sample deviation was 0.21.
(I'm also curious what you need such low latency for.)