Porting the Driver Subsystem

The driver subsystem provides OpenHarmony-dedicated APIs for peripheral device operations, including FLASH, GPIO, I2C, PWM, UART, and WATCHDOG APIs.

OpenHarmony provides two driver adaptation modes: using the driver subsystem and using the HDF driver framework. Because the resources of the mini system are limited, the IoT subsystem mode is recommended.

Procedure

Vendors need to implement their functions based on the interface definitions provided by OpenHarmony. The header files defined by the interfaces of the IoT subsystem are as follows:

base/iot_hardware/peripheral/
├── BUILD.gn
└── interfaces
    └── kits
        ├── iot_errno.h
        ├── iot_flash.h
        ├── iot_gpio.h
        ├── iot_i2c.h
        ├── iot_pwm.h
        ├── iot_uart.h
        ├── iot_watchdog.h
        ├── lowpower.h
        └── reset.h

The content of the base/iot_hardware/peripheral/BUILD.gn file is as follows:

import("//build/lite/config/subsystem/lite_subsystem.gni")
import("//build/lite/ndk/ndk.gni")
       
lite_subsystem("iothardware") {
  subsystem_components = [
    "$ohos_vendor_adapter_dir/hals/iot_hardware/wifiiot_lite:hal_iothardware",
  ]
}
if (ohos_kernel_type == "liteos_m") {
  ndk_lib("iothardware_ndk") {
    deps = [
      "$ohos_vendor_adapter_dir/hals/iot_hardware/wifiiot_lite:hal_iothardware", # Vendor dependent adaptation.
    ]
    head_files = [ "//base/iot_hardware/peripheral/interfaces/kits" ]
  }
}

As shown above, the directory for storing vendor adaptation interfaces is $ohos_vendor_adapter_dir/hals/iot_hardware/wifiiot_lite, where the target in the BUILD.gn file is hal_iothardware.

Example

1. Add the iot_hardware subsystem to the config.json file.

   Path: vendor/MyVendorCompany/MyProduct/config.json

   The sample code is as follows:

   { 
       subsystem": "iot_hardware", 
       components": [ 
           { "component": "iot_controller", "features":[] }
       ] 
   },
   

2. Add an adaptation file.

   In the vendor/MyVendorCompany/MyProduct/config.json file, set vendor_adapter_dir to //device/MyDeviceCompany/MyBoard/adapter.

   Perform adaptation in the vendor_adapter_dir directory.

   hals/iot_hardware/wifiiot_lite
   ├── BUILD.gn
   ├── iot_flash.c
   ├── iot_gpio.c
   ├── iot_i2c.c
   ├── iot_lowpower.c
   ├── iot_pwm.c
   ├── iot_reset.c
   ├── iot_uart.c
   └── iot_watchdog.c
   

   The content of BUILD.gn is as follows:

   static_library("hal_iothardware") {   # Target name
       sources = [                       # Source file adapted by the vendor
         "iot_watchdog.c",
         "iot_reset.c",
         "iot_flash.c",
         "iot_i2c.c",
         "iot_gpio.c",
         "iot_pwm.c",
         "iot_uart.c"
       ]
       include_dirs = [ ]
   }
   

   In the preceding example, include_dirs must contain two paths based on the site requirements:

   • Path to the header file of the IoT subsystem

   • Path to the SDK header file used by the IoT subsystem