Re: Add support of Wiegand card reader

["Gaëtan Carlier" <gcembed@gmail.com>]

Hello,
Thank you for your reply.

On 04/10/2018 01:26 AM, Matt Ranostay wrote:
> On Mon, Apr 9, 2018 at 7:05 AM, Gaëtan Carlier <gcembed@gmail.com> wrote:
>> Hello,
>> I would like to add support of Wiegand card reader [1]. Where can I place it : drivers/iio/access/wiegand.c or drivers/iio/security/wiegand.c?
> 
> Question here is why is this ideal for iio versus using the input subsystem?
What can I send to userspace from a bitstream using Input subsystem ?
Datas on Wiegand depend on readers used/setup. The best is to send bitstream directly to userspace and let user split bitstream into facilty/area code, card ID, ...
My idea is to send a structure with
    * number of bits read
    * if two parity bits are valid
    * the bitstream itself saved in a 64 bit unsigned integer (or a buffer of chars) including or not the parity bits (I still have to decide). I don't see readers with more than 60 bits.

I already start writting driver based on humidity/dht11.c that uses similar timings.

> 
> Also a few issues/points:
> 
> * What is the interface to the Wiegand data? If it is inputting on a
> GPIO that is for sure not going to be real time enough to get valid
> data
Wiegand protocol uses two data lines. Both data lines are pulled-up. When a 0 must be send, D0 line is set low, when a 1 must be sent, D1 line is set low. D0 and D1 line can never be set low at the same time. Reader will convert ID of the card into binary data flow of 26, 34, .... 60 bits.
The length of a data flow is configured in the reader and all readers connected on the same Wiegand bus have generally the same length.

> * Aren't there multiple Wiegand transport standards?
Yes they are several data length.

> * Most keyreaders I've seen are emulated as keyboard devices so they
> use the input subsystem.
If they are emulated as keyboard, they don't use Wiegand anymore ! Wiegand is still often used for hotels, ...

> * Also if the data being output is ASCII data, then I'm not sure that
> fits anywhere in iioData received from Wiegand bus are bits. They are not packed in 8 bits or any other size.

> 
> - Matt
> 
> 
>>
>> Thank you for your help?
>> Best regards,
>> Gaëtan.
>>
>> [1] https://en.wikipedia.org/wiki/Wiegand_interface
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Regards,
Gaëtan.