Re: CP2105 GPIO Pins

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Wed, Jan 13, 2016 at 5:10 PM, Martyn Welch
<martyn.welch@xxxxxxxxxxxxxxx> wrote:
> On 13/01/16 14:58, Linus Walleij wrote:
>>
>> (Adding Johan Hovold, serial-usb-maintainer)
>>
>> On Fri, Jan 8, 2016 at 12:14 PM, Martyn Welch
>> <martyn.welch@xxxxxxxxxxxxxxx> wrote:
>>
>>> I'm working on adding support to the cp210x driver for the optional GPIO
>>> pins available on Silicon Labs CP2105 USB to serial bridge.
>>
>>
>> Do you have a data sheet?
>
> Yes.

So can you share it or is it online somewhere?

>> I don't get it? Do you mean that the two serial ports will be able on
>> some serial port pins and then *also* on these extra pins in this
>> case, or do you mean that this is the only way for the serial
>> lines to get out of the chip?
>
> You loose DTR, DSR, DCD and RI on each serial port when GPIO is enabled on
> that port. Two of these pins on one port and 3 on the other become GPIO.
> Both serial ports are still available, but only provide TX, RX, RTS and CTS
> (which is more than enough for a lot of uses).

OK modem signals go out the window and instead these pins
are used for GPIO, because noone is using modems any more.
Makes perfect sense.

>> In any case, multiplexing is really a task for the pin control
>> framework, if you desire to switch this muxing at runtime.
>
> You can't do it at runtime. The choice is programmed into a PROM, typically
> at manufacture time (OEM, not chip) and can't be reverted.

OK then you should just go with the manufacturing setup
and you probably do not need pin control at all.

>> OK how do you determine this then?
>
> There are some vendor specific USB calls that can be used to determine this.

OK fair enough.

>> Isn't it possible to read/query the PROM about the settings?

And I guess that is what it does.

Looking forward to the patch :)

Yours,
Linus Walleij
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