170 lines
7.6 KiB
Markdown
170 lines
7.6 KiB
Markdown
the CuVoodoo USB hub is a 7-port USB 2.0 hub meant for device testing.
|
|
|
|
purpose
|
|
=======
|
|
|
|
most USB hubs are super cheap and crappy, leading to poor connection and data transfer.
|
|
there are industrial USB hubs, but they are bulky and very expensive.
|
|
to solve this issue I decided to design my own USB hub, tailored to my needs.
|
|
|
|
when developing and testing hardware, you often end with a lot of USB devices connected (serial debugger, programmer, logic analyzer, ...).
|
|
USB allows to have up to 128 devices, but only with a maximum depth of 7.
|
|
thus you are only allowed to have a maximum of 5 USB hubs between computer and devices, and I often have to plan my setup to not reach this limit.
|
|
most 7-port USB hubs use two 4-port USB hub, the seconds being connected to the first.
|
|
there are some exceptions to that, but they are rare, old, and often not advertised as such.
|
|
this heavily limits the actual number of end devices.
|
|
the CuVoodoo USB hub is a 7-port flat USB hub, preventing reaching this limit too fast.
|
|
|
|
the upstream and downstream USB ports are individually ESD protected.
|
|
this safety becomes important when developing, testing, and handling bare electronic devices.
|
|
this also comes in handy when connecting circuit with different ground potentials.
|
|
ESD protections already saved my day twice this way.
|
|
the issue is that they can blow without you noticing, but at least they protected the device once.
|
|
|
|
each output port is current limited to 500 mA.
|
|
no USB 2.0 device should draw more that this specified limit.
|
|
it if does, there is very probably an issue with the device.
|
|
this protection allows to isolate the faulty device and not have it affect all other connected devices, or the hub itself.
|
|
see `current limitation` below for more details.
|
|
|
|
each downstream port is power controlled.
|
|
this allows to remotely switch on and off individual devices.
|
|
this is an important requirement when developing and testing devices, which require a power cycle.
|
|
additionally, a switch next to the USB port can force the power off state.
|
|
|
|
the USB hub can be self-powered (through the USB input port), externally powered by 5V, or externally powered by anything between 6 and 40V.
|
|
this allows to use higher voltage power supplies to provide enough current to all ports.
|
|
the 5V are not feed back to the host.
|
|
|
|
each USB port comes with a high voltage output power port, connected to the high voltage input port.
|
|
this allows to power devices which require more than 5V, with a maximum or 5A, such as 12V externally powered devices.
|
|
these power outputs are controllable along the USB port.
|
|
as with the 5V USB power output, this allows to remotely switch on an off individual devices.
|
|
|
|
each port has status LEDs, indicating the speed and power status of the connected device.
|
|
|
|
the board uses proper impedance and differential signal routing to provide clean USB signals.
|
|
|
|
design choice
|
|
=============
|
|
|
|
USB 2.0
|
|
-------
|
|
|
|
this hub is only for USB 2.0 devices.
|
|
these are by far most of the devices I develop.
|
|
it makes it simpler and keeps the cost reasonable.
|
|
I often even disable USB 3.0 because of the 13-device limitation of the Intel xHCI.
|
|
when I need USB 3.0 for the very few devices, I connected them to the computer directly.
|
|
|
|
USB2517
|
|
-------
|
|
|
|
I wanted to use the FE2.1 7-port USB hub chip.
|
|
it does not need an external voltage regulator or crystal.
|
|
it is easier to solder thanks to its TQFP package, and provides all required functionalities.
|
|
sadly I could not find a source for the 64-pin packages, and the 48-pin variant does not provide all required functionalities.
|
|
thus I had to fall back to the Microchip USB2517, which uses a harder to solder QFN package.
|
|
|
|
power control
|
|
-------------
|
|
|
|
some USB hub chips allow to remotely control the power output on individual ports.
|
|
this capability is here also used to control the power on the higher voltage output.
|
|
thus you can completely power off even larger target devices.
|
|
|
|
current limitation
|
|
------------------
|
|
|
|
the USB hub has current limitation on the output.
|
|
this does limit the current to 500 mA, but only in constant current mode.
|
|
following current limiters have been tested:
|
|
|
|
- 0.5A PPTC fuse: it takes too long to trigger (> 1s), and switch off is not reliably detected
|
|
- MT9700: it has no over-current signal
|
|
- SY6288AAAC: the (fixed) current limit is not 0.6A, but around 1.5A
|
|
- TJ2242GSF6: over-current is only detected after 3s (instead of specified 100us, probably caused by thermal shutdown), and it is not signaled
|
|
- DIO7553ST6: works as expected and wished
|
|
|
|
the power distribution switch detects the over-current state and asserts the fault flag after 10 ms.
|
|
after 0.1 ms (as set in OC_TIMER, in Configuration Data Byte 2, in EEPROM) the hub will switch off power.
|
|
this also clears the over-current state.
|
|
after 100 ms the HUB will re-enable power.
|
|
this loop will repeat indefinitely.
|
|
no over-current is reported to the host in this case (when the over-current is cleared while power is off).
|
|
it is only reported when the OCS is asserted for longer (unknown time, with OCS kept low also when powered off).
|
|
this is a flaw of the USB2517, where the over-current is only reported if it can't control the power state.
|
|
I did not find a configuration option for this aspect in the datasheet.
|
|
|
|
LED color
|
|
---------
|
|
|
|
the USB specification, LEDs are used as port indicator (section 11.5.3)
|
|
|
|
- off: powered off/disconnected
|
|
- amber: current limitation reached
|
|
- green: enabled or transmitting
|
|
|
|
instead the following color scheme is used:
|
|
|
|
- green off: power off or over-current
|
|
- green on: power on
|
|
- red: low speed device connected
|
|
- blue: full speed device connected
|
|
- purple (red+blue): high speed device connected
|
|
- red and blue off: disconnected or in sleep
|
|
|
|
power output
|
|
------------
|
|
|
|
switching the power of the USB port also switches the 6-40V forward output.
|
|
when the 6-40V input is not connected, current/voltage feedback from the outputs is blocked.
|
|
|
|
usage
|
|
=====
|
|
|
|
it mainly works like a regular USB hub, at least when it comes to the data transfer.
|
|
just plug the device in a port.
|
|
|
|
power on the Downstream Facing Ports (DFPs) is only available when the Upstream Facing Port (UFP) is connected.
|
|
|
|
the hub can operate as bus powered (power coming from the UFP), but it would not be able to provide more than 500 mA across all DFPs.
|
|
it is preferable to connect an external 5V power supply to be able to provide 500 mA on all DFPs.
|
|
this will also turn the hub into self powered, not using any power from the UFP.
|
|
alternatively, you can connect a 6 to 40V power supply on the other power input.
|
|
the power for the hub and the 5V for the DFP will be derivate from this higher voltage supply.
|
|
the same higher voltage will be available on the power output next to the individual DFPs.
|
|
the hub will not switch on until the UFP USB port is connected.
|
|
|
|
a switch next to each DFP allows to turn off the power output on the USB and power ports.
|
|
the green LED is on when power output is available.
|
|
|
|
the power output on the USB and power ports can also be turned on/off remotely using standard USB commands.
|
|
this power output control is implemented in [uhubctl](https://github.com/mvp/uhubctl):
|
|
|
|
~~~
|
|
# list controllable USB hub ports
|
|
sudo uhubctl
|
|
# switch of port
|
|
uhubctl --action off --location 1-1.4 --ports 5
|
|
~~~
|
|
|
|
EEPROM
|
|
======
|
|
|
|
the USB2517 USB hub chip gets its configuration from an EEPROM.
|
|
to generate the configuration:
|
|
|
|
~~~
|
|
ruby eeprom.rb
|
|
~~~
|
|
|
|
this will create the `eeprom.bin` binary file.
|
|
feel free to adjust the configuration in the generating script, such as the serial number.
|
|
|
|
after having soldered all the parts on the board, connect a programmer (here a MiniPRO TL866xx) on the J4 pin header to write the AT24C02 EEPROM:
|
|
|
|
~~~
|
|
minipro --device "AT24C02@SOIC8" --write eeprom.bin -s
|
|
~~~
|