[sdiy] USB Question

[Vladimir Pantelic]

yes, that is doable
On Sep 23, 2015 7:08 PM, "Tim Ressel" <timr at circuitabbey.com> wrote:

> This will be for USB Midi, so the host connector needs to be powered and
> the device connector does not. But I should be able to sense power on the
> device connector and switch accordingly?  Default to host and switch to
> device upon power on the device connector?
>
> --TimR
>
> On 9/23/2015 9:56 AM, rsdio at audiobanshee.com wrote:
>
>> One correction to my comments: Whether your Device mode is self-powered
>> or not, you always need to be able to read the power coming from the USB B
>> connector to ensure that your CPU does not enable or drive the data lines
>> unless power is present. That's one of the basic rules of USB. So, this
>> means that your source for USB power over the A connector cannot connect to
>> the power on the B connector, otherwise you'll never know.
>>
>> The only thing missing from the EK-TM4C1294 LaunchPad is an example
>> circuit for a system with both A and B connectors, so that's where we're
>> getting into new territory. If anyone knows of an evaluation board that
>> does have both A and B - especially with schematics freely available - then
>> please share with the list.
>>
>> B
>>
>>
>> On Sep 23, 2015, at 9:47 AM, rsdio at audiobanshee.com wrote:
>> On Sep 22, 2015, at 11:28 PM, Vladimir Pantelic <vladoman at gmail.com>
>> wrote:
>>
>>> On 23.09.2015 08:10, Tim Ressel wrote:
>>>
>>>> I need to design a usb interface that does both host and device, but not
>>>> at the same time. There will be an A and B connector on the front
>>>> panel.  All of the procs I've looked at only have one USB interface.
>>>> I'm guessing the thing to do here is to use a USB switch.  Anyone have
>>>> some insights?
>>>>
>>> many CPU'S have a so called USB-OTG (on the go) interface that allows to
>>> switch roles between host and device.
>>>
>>> normally switching to host mode is done by inserting a cable that has
>>> the ID pin (the 5th pin on a USB mini/micro connector) grounded, but it
>>> can of course also be done under SW control.
>>>
>>> look at e.g. the STM32F105, it has a: "USB 2.0 full-speed
>>> device/host/OTG controller with on-chip PHY that supports HNP/SRP/ID"
>>>
>> Check out the Texas Instruments EK-TM4C1294XL LaunchPad (about US$20).
>>
>> It has an ARM Cortex-M4 with USB OTG and good source code examples. They
>> have examples of Host firmware and examples of Device firmware. The
>> documentation makes a big deal of the fact that none of the examples will
>> switch between Host and Device for you, so I imagine the solution is to
>> read the OTG input pin and then "reboot" into the other mode when it
>> changes. It doesn't seem like it will be too difficult. I've tested their
>> USB Audio Class Host firmware example, and it works fine. I assume that the
>> USB Device firmware is even simpler, and also functional.
>>
>> The EK-TM4C1294XL LaunchPad is also a good example of the circuit needed.
>> The technical manual for that LaunchPad has the full schematic. One
>> interesting component on the board is a chip that controls the current
>> being fed to the Host port to power the external Device. You'll need to
>> keep the power on the A and B connectors separate. It will be challenging
>> if you want to power your board entirely from USB when acting as a Device,
>> and probably much easier if your board is always self-powered. You'll need
>> to be able to read the B connector power on a 5-Volt-tolerant GPIO pin to
>> detect external power unless you're always self-powered. I think that the
>> ground and differential USB data can be shared between the A and B.
>>
>> I'm sure there are other options, but I wanted to point out that the
>> TM4C1294 has good examples for the circuits and source for the firmware.
>>
>> Brian Willoughby
>> Sound Consulting
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>>
> --
> --Tim Ressel
> Circuit Abbey
> timr at circuitabbey.com
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20150923/f3c4fc68/attachment.htm>