Hi Masahiro,
On 23 October 2014 09:29, Masahiro YAMADA yamada.m@jp.panasonic.com wrote:
Hi Simon,
I have questions of driver model serial.
The comment block in include/serial.h states .pending is optional
---------------------------->8-------------------------------
- pending() - Check if input/output characters are waiting
- This can be used to return an indication of the number of waiting
- characters if the driver knows this (e.g. by looking at the FIFO
- level). It is acceptable to return 1 if an indeterminant number
- of characters is waiting.
- This method is optional.
----------------------------8<-------------------------------
When I was testing my driver model conversion patch, I noticed ctrlc() function would not work without .pending handler.
The function ctrlc() calls tstc() and if it returns non-zero value, it also calls getc().
If .pending handler is not implemented, tstc() function always return 1, even if no input character is available in UART FIFO; As a result, getc() function will get stuck in
do { err = ops->getc(cur_dev); } while (err == -EAGAIN);
loop.
For example, "help" command does not work.
So, .pending is mandatory, isn't it?
One more question.
The comment says .pending is: Check if input/output characters are waiting
Should .pending check output buffer? or input only?
Yes it is actually mandatory, since we really don't want drivers to block in their getc()/putc() methods.
Output character check is required so we can implement flush. E.g. when we change the baud rate we should flush first.
Regards, Simon