-----Original Message-----
From: Tseng, Kuo-Lang [mailto:kuo-lang.tseng(a)intel.com]
Sent: Friday, February 26, 2016 12:29 PM
To: devel(a)lists.zephyrproject.org
Subject: [devel] RFC: Counter driver API

Hi,

As per suggestion from Gerrit comment, moving the discussion to mailing list.

Background
--------------

On Quark (SE and D2000), there are Always On Counter (free running) and
Always ON Periodic Timer devices. A counter|timer driver is to be added for
supporting these devices. At same time, the goal is to create an API that is
generic enough for not just these two specific devices.

Proposal:
-----------

Generic counter driver API:
-------------------------------
We will have 3 routines - start, stop, and read, which takes in the device pointer
- which identifies the timer. The driver header, counter.h, is under /include
folder:

/**
* @brief Set up counter configuration and start it.
* @param dev Pointer to the device structure for the driver instance.
* @param config Pointer to counter configuration structure
*
* @retval DEV_OK If successful.
* @retval DEV_* Code otherwise.
*/
int counter_start(struct device *dev, counter_input *config);

/**
* @brief Stop the counter.
* @param dev Pointer to the device structure for the driver instance.
*
* @retval DEV_OK If successful.
* @retval DEV_* Code otherwise.
*/
int counter_stop(struct device *dev);

/**
* @brief Read current counter value
* @param dev Pointer to the device structure for the driver instance.
*
* @return 32-bit value
*/
uint32_t counter_read(struct device *dev)

The counter_input structure can be something like below:

/**
* @brief Counter configuration.
*
* Acceptable setting in the configuration structure is hardware-specific.
*
* initial_value - Initial value to load to the counter or timer.
* callback - Callback function when timer expires.
*/
struct counter_input {
uint32_t initial_value;
void (*callback)(void);
};

Note - Using structure, tomorrow we can add more fields for a counter with
more features.
For the Free Running counter in Quark, these fields would be null as it does not
support interrupt or callback notification.

The hardware-specific driver implementation:
-----------------------------------

This can be implemented in /drivers directory. For example, for Quark SE and
D2000, we can have below file which implements the API functionality using the
AON Counter and AON Periodic Timer:

drivers/quark_aon_counter.c

Comment, feedback welcome.