Boot Time Optimization in WEC7 OS for i.MX6 Sabre SDP
iWave, a reliable embedded solutions provider has now optimized the booting time of its Windows Embedded Compact 7 (WEC7) BSP for Freescale’s SABRE SDP/B platform. Now the WEC7 OS is booting in a short period of time ~3 seconds for a small footprint OS image with display and touch drivers support, and boot time of ~8 to ~10 seconds for an OS image with basic drivers and OS components support.
Why boot time optimization?
WEC7 is a real time OS which will be used in performance-critical applications such as automotive and healthcare units. In most of the cases, booting time will play important role, e.g. if the device is used in rear-view camera system in automotive field, the user needs the device to start working as soon as the reverse-gear is applied. This requirement needs the device to boot and start the camera application within few seconds. This demands a very short OS boot time. Some of the techniques which can be applied for efficient boot time optimization are discussed in this article.
Boot phases in WEC7:
- Boot-loader (eboot)
- Copying of OS image from booting device (e.g. Micro-SD) to RAM
- OAL Layer
- Driver initializations and file system mounting
Guidelines for reducing the boot time in different booting phases of WEC7:
Remove the code that initializes a hardware which is not required in boot-loader. E.g. If booting device is micro-SD, the initialization of NAND is not necessary. So, this redundant code needs to be removed. The eboot menu in eboot is important for debugging of WEC7 OS. But it is not needed in an end product. So, the delay for this eboot menu can be completely removed to reduce 3 seconds of time. In few platforms such as Freescale’s SABRE platform, a default splash screen is used, which updates continuously. This can be removed, and a static splash screen can be displayed, which can save a few milliseconds of time. Remove unnecessary serial debug prints.
Copying of OS image from booting device (e.g. Micro-SD) to RAM:
This time increases as the size of WEC7 OS image increases. So, select the OS components carefully and remove redundant components from OS image so that the OS image can be copied to RAM quickly. Also remove unnecessary registry keys, dlls and libraries to reduce the OS size. Optimize binary image builder (.bib) file to reduce the run-time image file. Implement Multi-BinFS OS binaries to reduce the OS copying size. As the functionalities/driver supports goes on increasing, WEC7 image size increases. So, the time required to copy the image increases, and RAM size needed to store the OS image increases.
The Binary ROM Image File System (BinFS) can fix the two issues. In a BinFS file system, the WEC7 OS binary is divided into multi-binary Image files, and only the one binary (less than 5MBs) is copied into the RAM by the boot-loader. The components in the other binary files are copied into the RAM only when they are required to run. Links that can be referred to implement multi-BinFS in WinCE:
MSDN documentation: http://msdn.microsoft.com/en-us/library/aa516960.aspx;
An implementation guide by Freescale: http://cache.freescale.com/files/dsp/doc/app_note/AN4137.pdf
You can also include compressing-decompressing mechanisms in boot-loader to achieve even shorter copying time.
Remove the code that does unnecessary hardware implementations. Skip the initializations that already done in eboot. Remove any wait/loop/delay if exists. Remove unnecessary serial debug prints.
Driver initializations and file system mounting:
Analyse and remove all the redundant drivers, check for any loop, wait or delay sequences in driver initialization code. Load any applicable drivers (e.g. USB, sensors) after the OS boot (i.e. after user sees a desktop/application). In WEC7 OS, a driver can be either loaded during booting using device manager/GWES, or can be loaded dynamically whenever necessary. This can be achieved easily by changing the registry key configurations to remove the driver from built-in drivers, a small application to load the driver after OS boot-up, and registry settings to launch this application automatically once the OS is booted. To decide the load order, it is important to check the dependencies of/on a driver. Use appropriate splash screen/progress bar while user waits for OS booting. Remove unnecessary serial debug prints.
By effectively following the techniques mentioned, WEC7 based platforms can achieve reduced boot time for quick application access.
iWave has optimized the WEC7 booting time on Freescale’s SABRE SDP platform. The booting time is as low as ~3 seconds for a WEC7 OS with standard shell, LCD display, DDraw, I2C and touch driver support, and ~8 to 10 seconds for WEC7 OS with following components:
- Standard shell
- Capacitive touch screen
- USB host – Mass storage and HID
- GPU (OpenVG/GL)
- Multimedia codecs
- Video Playback
- Ambient Light Sensor
- Debugging using KITL
Keshava G N - Member Technical (Software)
iWave Systems Technologies