This document provides an introduction and overview of G sensor I2C drivers on Android. It discusses what a G sensor is and its applications. It then covers the key aspects of implementing an I2C driver for a G sensor from initializing the driver and registering it, to detecting and probing devices, and creating I2C clients. Issues that may occur and how to resolve them are also addressed.

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

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

3. 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.

4. Orientation estimation

5. Orientation estimation

6. Stability check STABLE_THRES STABLE_COUNT_MIN calling rate? bigger or smaller?

7. Code Review

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

9. 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.

10. 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)

11. 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

12. Legacy driver: address_data

13. 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

14. 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);

15. 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;

16. 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)

17. 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] == '\0‘ to check driver->detect function /* Detection succeeded, instantiate the device */ client = i2c_new_device (adapter, &info); list_add_tail (&client->detected, &driver->clients);

18. 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; ……… ..

19. 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.

20. 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));

21. I2c Driver: file_operations

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

23. 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

24. Demo To Do: jni module

25. Reference Linux Device Drivers, Third Edition

26. Thank You.