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Real-Time Concepts for Embedded SystemsThis boot scenario is shown in Figure 3.5. Figure 3.5: Boot sequence for an image executing from RAM after transfer from the host system. The first six steps are identical to the initial boot scenario. After completing those steps, the process continues as follows: 7. The application image is downloaded from the host development system. 8. The image integrity is verified. 9. The image is decompressed if necessary. 10-12. The debug agent loads the image sections into their respective run addresses in RAM. 13. The debug agent transfers control to the download image. There is a good reason why the memory area used by the debug agent is not recycled. In this example, the downloaded image contains an RTOS, which is introduced in Chapter 4. One of the core components of a RTOS is a scheduler, which facilitates the simultaneous existence and execution of multiple programs, called tasks or threads. The scheduler can save the execution state information of the debug agent and revive the agent later. Thus, the debug agent can continue to communicate with the host debugger while the downloaded image executes, providing interactive, visual, source-level debugging. 3.4 Target System Software Initialization Sequence The target image referred to repeatedly in the last section is a combination of sophisticated software components and modules as shown in Figure 3.6 ...» |
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