Detailed description of the VxWorks Startup Process (Part 1)

VxWorks has three types of images:

There are three file types for VxWorks Image

1. Loadable images: boot-Rom guides you through the network port or serial port to download to ram
2. ROM-based images (compression/no compression): this means that the image is directly burned into the Rom, and the image is then run into RAM during the runtime.
3. Rom-resident images: The instruction part of the image resides and runs in the Rom. Only the part of the data segment is merged into RAM.

Note that all the three images mentioned here contain images of the real operating system VxWorks. The latter two images can be started and run directly, but the first one does not, it can only run with another image called Boot Image (which can be generated in build-> build boot Rom in tornado, that is, boot image is used to boot and then download the loadable image that actually contains VxWorks through the network port or serial port before it can run. That is to say, the boot image is used with loadable image.

There are four types of image files. Let's take a look at their composition:

1. Boot Image: contains a program called Bootstrap programs + a ROM Boot Program program.
2. Loadable images: an image composed of the Operating System VxWorks and applications.
3. ROM-based images (compressed/uncompressed): contains a bootstrap programs program + loadable images (that is, an image composed of the Operating System VxWorks and applications)
4. Rom-resident images: Same as above

We can see from the above that ROM-based images, Rom-resident images, Boot Image

All three images contain a program called Bootstrap programs, which has the startup function. You can copy the code segments and data segments in the Rom to ram. Let's take a look at the three VxWorks startup processes:

• Boot Image + loadable images:

We have said that loadable images is started by loading the boot image. First, the bootstrap programs program in the boot image loads the Boot Program program to ram_high_adrs in Ram, and then the control is handed over to the boot program, boot Program is responsible for a series of simple hardware initialization (network port, serial port, etc.), and starts Downloadable images (including the application's VxWorks operating system) to ram_low_adrs, then, the control is handed over to the VxWorks operating system for execution.

The following figure shows a simple flowchart. The following figure 2 shows a more detailed flowchart.

Figure 1

Figure 2 (1)

 

Figure 2 (2)

• ROM-based images (compressed/not compressed ):

This kind of image can be started directly because it contains the bootstrap programs program. Therefore, boot programme is not required for this kind of image. First, bootstrap programs is started, load VxWorks from the image to ram_low_adrs in the memory and start running. Figure 3 is a simplified diagram, and figure 4 is a more detailed flowchart.

 

 

Figure 3

Figure 4

• Rom-resident images:

The loading of such images is basically the same as that of the previous one, except that only data and BSS segments are loaded.