Introduction to Android G Sensor I²C Driver on Android

Introduction to Android G sensor I²C Driver on Android Bo-Yi Wu 2010.06.04 Gemtek Technology Co., Ltd

Outline
What’s G sensor ?
I²C Driver
Kernel Patch
Issue
Reference

What’s G sensor & Application
As accelerometers are more and more present in mobile devices, new features are developed. Portrait & Landscape is one of them. It allows devices to display the information in the right orientation depending on how it is held.

Orientation estimation

Stability check
STABLE_THRES
STABLE_COUNT_MIN
calling rate? bigger or smaller?

Code Review

I²C : detection capability set i2c address value detect call back function detect address fill the structure i2c_board_info

New-style drivers vs Legacy drivers
Legacy drivers duplicate a lot of code .
The code needed in each driver to implement a detect callback is way smaller than the code needed to implement a legacy driver.

New-style drivers: initial function
module_init ( BMA150_init );
return i2c_add_driver (&bma150_driver);
module_exit ( BMA150_exit );
i2c_del_driver (&bma150_driver);
__exit && __init (Kernel built in or module)

G Sensor: bma150_driver structure
New-style driver
Legacy driver probe: Callback for device binding (new-style drivers) remove: Callback for device unbinding (new-style drivers) class : What kind of i2c device we instantiate (for detect) (1<<0) for sensor address_data: The I2C addresses to probe, ignore or force (for detect) id_table: List of I2C devices supported by this driver

Legacy driver: address_data

New-style drivers: address_data /* Internal numbers to terminate lists */ I2C_CLIENT_END : 0xfffeU I2C_CLIENT_INSMOD_1 ~ I2C_CLIENT_INSMOD_8 I2C_CLIENT_INSMOD_COMMON : define structure address_data normal_i2c, probe, ignore value

I2c Driver: i2c_register_driver 1. new style driver methods can't mix with legacy ones /* check bma150_driver is news style driver or not */ is_newstyle_driver (driver) 2. /* check bma150_driver is Legacy style driver or not */ driver->attach_adapter || driver->detach_adapter || driver->detach_client 4. /* add bma150 driver to list for i2c only */ INIT_LIST_HEAD (&driver->clients) 5. /* Walk the adapters that are already present */ class_for_each_device struct i2c_adapter *adapter = to_i2c_adapter(dev); struct i2c_driver *driver = data; 3. /* register driver with bus, and use bus_add_driver () to add bus driver */ driver_register (&driver->driver);

I2c Driver: __attach_adapter
Call __attach_adapter function
New style driver:
i2c_detect (adapter, driver);
Legacy driver:
driver-> attach_adapter (adapter);
/* Because Legacy driver don’t have detect function */ if (!driver-> detect || !address_data) return 0;

I2c Driver: i2c_detect
/* initial i2c client structure */
struct i2c_client *temp_client; temp_client->adapter = adapter;
/* get address from i2c_client_address_data*/
address_data = driver ->address_data;
/* check if Legacy driver */
if (! driver ->detect || ! address_data )
/* check normal_i2c ignore probe address */
for(i = 0; address_data ->normal_i2c[i] != I2C_CLIENT_END ; i += 1)

I2c Driver: i2c_detect_address
/* Make sure the address is valid */
( addr < 0x03 || addr > 0x77 )
/* Make sure there is something at this address */
i2c_smbus_xfer (adapter, addr, 0, 0, 0, I2C_SMBUS_QUICK , NULL)
/* Finally call the custom detection function */
memset(&info, 0, sizeof(struct i2c_board_info));
driver-> detect (temp_client, kind, &info);
use info.type[0] == '‘ to check driver->detect function
/* Detection succeeded, instantiate the device */
client = i2c_new_device (adapter, &info);
list_add_tail (&client->detected, &driver->clients);

I2c Driver: i2c_new_device
Set i2c_client info from i2c_board_info structure
strlcpy (client->name, info->type, sizeof(client->name));
client->addr = info->addr;
client->irq = info->irq;
……… ..

I2c Driver: i2c_device_match
I2c_bus_type is used on new-style driver
i2c_device_match
match client i2c_device_id table && i2c_client table id
i2c_device_probe
Call bma150_probe function if you defined driver’s probe.

I2c Driver:bma150_probe
/* bma150 device create ok if return 0*/
misc_register (&bma_device);
/* initial data */
data->smb380. bus_write = bma150_i2c_write;
data->smb380. bus_read = bma150_i2c_read;
data->smb380. delay_msec = bma150_i2c_delay;
data->smb380. dev_addr = client->addr;
smb380_init(&(data->smb380));

I2c Driver: file_operations

Build Linux Kernel
Edit Kconfig & Makefile
Patch all files(bma150_drivers.c…)
Make menuconfig
Make uImage

Issue: can’t create device
/* Make sure there is something at this address */
i2c_smbus_xfer (adapter, addr, 0, 0, 0, I2C_SMBUS_QUICK , NULL)
Please edit i2c_smbus_xfer_emulated function and
Change message data length: 0 -> 1

Demo To Do: jni module

Reference
Linux Device Drivers, Third Edition

Thank You.

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Introduction to Android G Sensor I²C Driver on Android

by Bo-Yi Wu on Jun 06, 2010

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