Platform Builder: Running without a Bootloader

There was a question about running Windows CE without a bootloader in the Platform Builder newsgroup this morning. The poster suggested that KITL required a bootloader and asked if the OS required a bootloader in general.

The simple answer, and the one that I replied with, is no. The OS does not require a bootloader. KITL does not require a bootloader. But, the BSP may require a bootloader. Without looking at any specific BSP, here are some of the reasons that a BSP might require a bootloader.

· KITL – many BSPs from chip vendors and Microsoft set up KITL using data setup in the bootloader. They do this with some data structure at a fixed location in RAM. So for these to run KITL without a bootloader, these BSPs will need to be modified to initialize KITL in a different way.

· CPU and RAM initialization – many BSPs initialize the CPU registers and RAM in the bootloader and then skip this initialization in the kernel. So to run without a bootloader changes will need to be made to the OAL.

· Other – anything else that is initialized on the bootloader will need to be initialized in the OAL.

This might be general, but there are many ways to write a bootloader and OAL so every BSP will be different. Removing the bootloader can be done, but it is a radical architectural change that will require some effort to accomplish.

Friday, January 02, 2009 11:12 AM

Your Comments.

# re: Platform Builder: Running without a Bootloader

On some devices (those that don't have a "BIOS" or other kind of firmware/ROM that allows the device to boot in alternative ways) removing the loader may make updates of the whole OS complex or risky. The OS image may not be updated correctly (for a power failure, a fatal error etc.) and this could leave you with a "bricked" device. Having a loader that is independent form the OS image and can update it can avoid this kind of problems. If the OS update fails, you can reboot and retry.
On the other side implementing some kind of hardware access (ex: a USB mass storage device) may require a lot of code (accessing the USB host, implementing the mass-storage protocol, handle the filesystem) and you can't easily reuse the code provided with Window CE because it requires the full OS to run. Sometimes I suggest to have two images on the device, the "real" one, and a very small one that is used only to update the main one or to do some low level test on the hardware to check that it's working. In this way you have a small and simple loader (no needs to update it), an OS image that can access all the features and devices supported by CE to perform OS upgrades (even upgrade via FTP, for example), and your "real" image that you may upgrade in a safe way when needed. CE is quite compact and the upgrade image with a minimal GUI can require 3-4MB, not much more than a complex loader.

Left by Valter Minute at 1/3/2009 3:47 AM

# re: Platform Builder: Running without a Bootloader

I guess that I did forget to mention that removal of the bootloader would also remove the "loader" functionality.

Bruce

Left by Bruce Eitman at 1/3/2009 9:55 AM

# re: Platform Builder: Running without a Bootloader

Is CE OS can run without bootloader. i means is OS doesn't required any boot argument during first time boot.

If this possible how to do this? i have initialize the RAM from BIOS+xldr (form CPU onchip SRAM) and then what to put the OS at RAM and executes from RAM without eboot.
But i am unable to do so, OS will endup at exception.
Can anyone put some light on problematic area and entry point of WinCE6.0 OS.
Thanks in advance .
Prabhat

Left by Prabhat Shrivastav at 1/15/2009 1:21 AM

# re: Platform Builder: Running without a Bootloader

Praphat:

The point of this post is that a bootloader is not a requirement for running the OS.

But, removal of the bootloader is a significant architectural change to most BSPs. Nobody can answer why your specific OS is failing, only you can do that with carefull engineering and debugging.

I suppose the real question that you should be considering is why are you removing the bootloader? Is there a different solution to your requirement? Could you instead remove functionality from the bootloader and meet the requirement, and your deadline?

Brue

Left by Bruce Eitman at 1/15/2009 8:21 AM

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# re: Platform Builder: Running without a Bootloader
On some devices (those that don't have a "BIOS" or other kind of firmware/ROM that allows the device to boot in alternative ways) removing the loader may make updates of the whole OS complex or risky. The OS image may not be updated correctly (for a power failure, a fatal error etc.) and this could leave you with a "bricked" device. Having a loader that is independent form the OS image and can update it can avoid this kind of problems. If the OS update fails, you can reboot and retry.
On the other side implementing some kind of hardware access (ex: a USB mass storage device) may require a lot of code (accessing the USB host, implementing the mass-storage protocol, handle the filesystem) and you can't easily reuse the code provided with Window CE because it requires the full OS to run. Sometimes I suggest to have two images on the device, the "real" one, and a very small one that is used only to update the main one or to do some low level test on the hardware to check that it's working. In this way you have a small and simple loader (no needs to update it), an OS image that can access all the features and devices supported by CE to perform OS upgrades (even upgrade via FTP, for example), and your "real" image that you may upgrade in a safe way when needed. CE is quite compact and the upgrade image with a minimal GUI can require 3-4MB, not much more than a complex loader.

Left by Valter Minute at 1/3/2009 3:47 AM
# re: Platform Builder: Running without a Bootloader
I guess that I did forget to mention that removal of the bootloader would also remove the "loader" functionality.

Bruce

Left by Bruce Eitman at 1/3/2009 9:55 AM
# re: Platform Builder: Running without a Bootloader
Is CE OS can run without bootloader. i means is OS doesn't required any boot argument during first time boot.

If this possible how to do this? i have initialize the RAM from BIOS+xldr (form CPU onchip SRAM) and then what to put the OS at RAM and executes from RAM without eboot.
But i am unable to do so, OS will endup at exception.
Can anyone put some light on problematic area and entry point of WinCE6.0 OS.
Thanks in advance .
Prabhat

Left by Prabhat Shrivastav at 1/15/2009 1:21 AM
# re: Platform Builder: Running without a Bootloader
Praphat:

The point of this post is that a bootloader is not a requirement for running the OS.

But, removal of the bootloader is a significant architectural change to most BSPs. Nobody can answer why your specific OS is failing, only you can do that with carefull engineering and debugging.

I suppose the real question that you should be considering is why are you removing the bootloader? Is there a different solution to your requirement? Could you instead remove functionality from the bootloader and meet the requirement, and your deadline?

Brue

Left by Bruce Eitman at 1/15/2009 8:21 AM

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