Building a software serial driver

[Pranay Srivastava]

On Tue, Jun 24, 2014 at 11:49 PM, Torrie Fischer
<tdfischer at hackerbots.net> wrote:
> Apparently all I had to do was set the type attribute on the uart_port
> structure to anything that isn't PORT_UNKNOWN.
>

Arhh.. I see. I overlooked that since tty->type was being set. Good to
know you got it working.

> Here's a functional driver that takes a GPIO pin and creates a read-only
> serial TTY:

So multiple open don't harm? The startup routine is called only once
is that right?

>
> https://github.com/tdfischer/gpio_serial/blob/master/gpiotty.c
>
> :)
>
> On Tuesday, June 24, 2014 21:27:46 Pranay Srivastava wrote:
>> Hi Torrie,
>>
>> On Tue, Jun 24, 2014 at 6:26 PM, Torrie Fischer
>>
>> <tdfischer at hackerbots.net> wrote:
>> > Hi, Pranay.
>> >
>> > Thanks for having a look.
>> >
>> > On Tuesday, June 24, 2014 13:42:35 Pranay Srivastava wrote:
>> >> I looked at uart_register code, it seems there's no read callback so
>> >> that's why you are getting that -EIO.
>> >
>> > From what I understand, I'm supposed to set up the interrupts needed in
>> > the
>> > startup function which is called when the device is opened. This never
>> > happens though, as adding a printk results in no output.
>>
>> I think this might be causing it, if you see tty_open then it has a call to
>> ,
>>
>> tty_open_current_tty , this seems to be the only one which I think is
>> not making the driver being looked up and hence no uport->open
>>
>> so in case there's an already a tty attached to current then i think
>> it isn't opening
>> a new one. Maybe you need to detach this tty? Not so sure I'll look
>> again what can be done.
>>
>> >> I think you can put this call in your start_tx since uart_start is
>> >> calling port->start_tx at the end so i guess you should be good there.
>> >
>> > I suspect that start_tx is not getting called since adding a printk in my
>> > start_tx function doesn't result in any output.
>> >
>> >> I don't have much idea how will you read from it though.
>> >
>> > I'm able to read from it by waiting for a rising edge interrupt and then
>> > bit- banging the GPIO line in userspace, though at a slow baud that is
>> > unusable. I need 9600 to read from my device :)
>>
>> Ok good!. I don't have much idea about GPIO. While searching I found
>> there's a GPIO library for Raspi. I don't know how much help that
>> would be but i
>> guess you don't want to use it.



-- 
        ---P.K.S