2009/3/6 <microbit@xxxxxxxxxxxxxxxxxxxxxx>
Can you make it simple please ...as simple as the question .. ?> Anyway in any case how does shell get the 'd' or anything from theI'm a Linux kernel newbie, (although I have heavy embedded MCU coding
> keyboard?
> What are the exact steps?
background) but I can help with the general approach of this scenario.
First, it's important to note that any interrupt handler should be as
*short* as possible.
This applies to any CPU/MCU system. Once the handler (ISR) has acted upon
the event, it will have relevant data stored somewhere, which then the OS
or "foreground" code can act upon. This is commonly referred to as "bottom
half".
For a keyboard handler, it will typically use a ring buffer (OSs will use
queues). The ring buffer will have a pointer to the head (where the latest
or newest data was stored) and the tail (where the oldest data resides).
When head and tail are equal the ring buffer is empty.
In your example, the head pointer will point to the character 'd' and the
tail will be one behind.
It's most convenient (and fastest) to assign a buffer size of a power of
2.
Note that at this stage it's not per se necessary that further interrupts
or task yielding occurs.
The application code could do something as simple as polling whether there
is data in the buffer by looking at the head/tail pointers on a frequent
basis.
In the case of an OS, the task of retrieving and processing the keyboard
data will activate if it wasn't active.
Where that keyboard data then is off to will depend on what
shell/application/process is running. The received 'd' character might even
just sit there in the buffer but no one is interested in it...
Perhaps that gives a very general insight at machine level of what goes on.
--
With Love..
. .Shinooooo
