In the healthcare industry, operating systems in human-machine interfaces often adjust the brightness and color of different LED light bars based on the patient’s condition. This section will share a complete LightBar solution based on the Android system. It covers the implementation of functionalities from the low-level stage driver porting to application layer, followed by the development of the JNI library and the integration with the APK. Through this, we aim to provide insights into how to implement special peripheral devices in the Android Open Source Project (AOSP).

1. Implementing a LED Light Bar
Solution on Android System
LC Wang, Wig Cheng
30 July 2023

2. OUTLINE
• PART I. System Part (Presented by Wig Cheng)
Implementing JNI function in system
• PART II. APK Part (Presented by LC Wang)
Implementing a demo APK using JNI library

3. PART I.
• Me
• Motivation
• System architecture
• AOSP Kernel driver tweaking
• LIBUBOOTENV porting
• JNI implementation
• Summary

4. ME
• Name: Wig
• Job: IEIWorld - Android OS team
• Work
#> Embedded Linux platforms
#> Industrial Android BSP
• GITHUB: https://github.com/wigcheng

5. CLASSICANDROID PORDUCTS
Refer from google search

6. OTHERANDROIDAPPLICATIONS
Refer from google search

7. MOTIVATION
• In healthcare use case which need LED color for a patient’s
health status. In this case, we'll show you a LED light-bar
solution using Android OS.

8. MOTIVATION (CONT'D)
Power on APP Sleep (Suspend) Power off
System Status Power on Power on Sleep Power off
Power LED Off Off
Color Blinking
default: Blue
On/off (Red)
default: On
User LED Off
1. LED control
2. Wave/Breath mode
3. Sleep/Power off setting
Off Off
blinking
blinking
Specifications

9. MOTIVATION (CONT'D)
Specifications
LED light bar
LED light bar
Power LED
User LED User LED
Power LED
Platform:
- NXP ARM Cortex-A53 IMX8MM
Supported OS:
- Android 12, Kernel 5.10.72
- Android 13, Kernel 5.15.74

10. SYSTEM ARCHITECTURE
Hardware
U-boot
AOSP Kernel
ART
JNI Layer
APP Layer
1. Enabling LightBar driver with device tree
2. Tweaking driver
AOSP
1. libubootenv library porting
2. Checking LED nodes
3. SELINUX
1. Add LightBar related boot argument
1. DesignAPIs for APK
1. Design demo APK

11.  TI TLC59116 LED driver IC
 16 channels
 via I2C bus
 PWM control method
 Linux upstream driver
 Enable driver in defconfig
 Add to device tree
 Tweaking driver (later)
AOSP KERNEL DRIVER
• Normal defconfig
<source>/vendor/nxp-opensource /kernel_imx /arch
/arm64/configs/iei_imx_android_defconfig
• GKI (Google Kernel Image) defconfig
<source>/vendor/nxp-opensource
/kernel_imx /arch /arm64/configs/imx8mm_gki.fragment
CONFIG_LEDS_TLC591XX=m (build as kernel module)
master SDA
SCL
slave 1 slave 2

12. lightbar1: tlc59116_left@60 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "ti,tlc59116";
reg = <0x60>;
status = "okay";
out0@0 {
label = "i2c2_led_red_00";
reg = <0x0>;
};
….....
….....
out14@e {
label = "i2c2_led_blue_04";
reg = <0xe>;
};
};
I2C device address 0x60
Driver name
Link to <kernel source>/drivers/leds/leds-tlc591xx.c
static const struct of_device_id of_tlc591xx_leds_match[] = {
{ .compatible = "ti,tlc59116",
.data = &tlc59116 },
{},
};
MODULE_DEVICE_TABLE(of, of_tlc591xx_leds_match);
LED-0 node: id = 0x0, node name = "i2c2_led_red_00"
device node path:
/sys/bus/i2c/drivers/tlc591xx/1-0060/leds/i2c2_led_red_00/brightness
LED1 ~ LED13 definition
/sys/bus/i2c/drivers/tlc591xx/1-0060/leds/i2c2_led_red_01/brightness
/sys/bus/i2c/drivers/tlc591xx/1-0060/leds/i2c2_led_red_02/brightness
….
/sys/bus/i2c/drivers/tlc591xx/1-0060/leds/i2c2_led_blue_03/brightness
LED-14
/sys/bus/i2c/drivers/tlc591xx/1-0060/leds/i2c2_led_blue_04/brightness
Modify device tree

13. AOSP KERNEL DRIVER (CONT.D)
 CONFIG_LEDS_TLC591XX → drivers/leds/leds-tlc591xx.c
static struct i2c_driver tlc591xx_driver = {
.driver = {
.name = "tlc591xx",
.of_match_table = of_match_ptr(of_tlc591xx_leds_match),
.pm = &tlc591xx_pm_ops,
},
.probe = tlc591xx_probe,
.shutdown = tlc591xx_shutdown,
.id_table = tlc591xx_id,
};
Add to driver for suspend/resume function
add LED blinking behavior to suspend function
add clear LED state behavior to resume function
static SIMPLE_DEV_PM_OPS(tlc591xx_pm_ops,
tlc591xx_suspend, tlc591xx_resume);
Add to driver for power-off function
add turn on red color for LED to shutdown function
Modify driver

14. LIBUBOOTENV PORTING
 New tool in 2021 (DENX)
 Feature – modify bootargs in rootfs of Linux OS
 Port to AOSP
 Source path: <source>/external/libubootenv
 Add Android.bp (Makefile)
 Output file
 /vendor/lib64/libubootenv.so (library)
 /vendor/bin/fw_printenv (utility)
 /vendor/bin/fw_setenv (utility)
 /vendor/etc/fw_env.config (config)
eMMC address:
/dev/block/mmcblk2 0x400000 0x4000
device name offset address env size
Tracing U-boot defconfig
<u-boot source>/configs/xxx_android_defconfig
CONFIG_ENV_SIZE=0x4000
CONFIG_ENV_OFFSET=0x400000

15. JNI IMPLEMENTATION
 Implement via C/C++ -> LightBar.cpp
 Bridge using CMAKE configuration
 API definition
 setLightBarUserLED
 clearLightBarLED
 setLightBarBreathMode
 setLightBarWaveMode
 setLightBarPowerLedSuspendColor
 setLightBarPowerLedPoweroffState
 getLightBarPowerLedStatus
JAVA Base
Kotlin Base
LightBar.cpp
JniMethod.java
MainActivity.java
JniMethod.kt
MainActivity.kt

16. JNI IMPLEMENTATION (CONT.D)
 Implementation flow
 User LED controlling
 Power LED controlling
Open specific LED
brightness node
/sys/bus/i2c/drivers/tlc591xx/1-0060/leds/i2c<bus>_led_<color>_<number>/brightness
/sys/bus/i2c/drivers/tlc591xx/3-0060/leds/i2c<bus>_led_<color>_<number>/brightness
read/write brightness node close brightness node
Adapt fw_setenv command
popenAPI pclose
Adapt fw_printenv command
Suspend argument: leds.suspend_color="<color>"
support color list: red, green, blue (default), yellow, cyan, magenta, white
Power-off argument: leds.poweroff_state="<status>"
support state list: on, off

17. U-boot environment arguments
1. Save to eMMC specific
address
2. Add power LED relate
argument
SUMMARY
Kernel driver (as a module)
1. Load power LED arguemnt
from u-boot arguments
2. Initial drivers with specific
functions
libubootenv
1. Load power LED arguemnt
from u-boot arguments in
ART stage
2. Set power LED argument to
u-boot environment (need
reboot)
Implement JNIAPI to APK
development

18. PART II.
 Me
 App architecture
 App java design
 App JNI design
 SELinux
 Troubleshooting

19. ME
• Name: LC
• Job: IEIWorld - Android software engineer
• GITHUB: https://github.com/lc-wang

20. APP ARCHITECTURE
UI
JNI
Build Setting

21. APP JAVA DESIGN

22. APP JAVA DESIGN

23. APP JAVA DESIGN
BreathMode WaveMode

24. APP JNI DESIGN

25. APP JNI DESIGN
package name_Java file_name_function name

26. APP JNI DESIGN

27. APP POWER LED
Power Suspend
Power Off

28. SELINUX
Linux DAC
DAC: Discretionary Access Control
directory
read
write
execute
Owner Group Other
uid gid

29. SELINUX
User process makes a system call
system call
DAC check
LSM check
User space
Kernel space
LSM: Linux Security Module

30. SELINUX
Command: ls –lZ / ps -lZ
drwxr-xr-x 15 root root u:object_r:system_file:s0 330 2023-07-13 10:01 system
SELinux user
role
domain
Multi-Level Security

31. SELINUX
allow system_app system_app_data_file:notdevfile_class_set rw_file_perms;
File: system_app.te
rule source type
(domain)
target type
(domain)
class perm_set

32. SELINUX
Ligtbar fw_setenv /dev/block/mmcblk2
system app vendor_file block_device_file
process/file
domain

33. SELINUX
Ligtbar fw_setenv /dev/block/mmcblk2
system_app vendor_file block_device_file
allow system_app system_app_data_file:notdevfile_class_set rw_file_perms;
allow system_app cache_recovery_file:dir { search write add_name };
…
allow system_app vendor_file:file {read write};
allow vendor_file block_device_file:blk_file {read write};

34. SELINUX
Ligtbar fw_setenv /dev/block/mmcblk2
File: {AOSP root}/system/sepolicy/public/domain.te
neverallow neverallow
system_app vendor_file block_device_file

35. SELINUX
File: system_app.te
allow system_app system_app_data_file:notdevfile_class_set rw_file_perms;
allow system_app cache_recovery_file:dir { search write add_name };
…
permissive system_app;
Ligtbar fw_setenv /dev/block/mmcblk2
system_app vendor_file block_device_file

36. TROUBLESHOOTING
allow system_app system_app_data_file:notdevfile_class_set rw_file_perms;
allow system_app cache_recovery_file:dir { search write add_name };
…
permissive system_app;
Breaking the Android rule, it causes CTS/VTS cases fail
! ! !

37. SUMMARY
• App UI
• App JNI
• How to solve SELINUX Issue

38. OPEN SOURCE
 Light bar JNI SDK instruction
https://github.com/ieiARMCommunity/lightbar_sdk_aosp
 Light bar demo APK source code
https://github.com/QNAP-android-internal/IEI-AndroidLightBar