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USING A BOOT MONITOR IN EMBEDDED SYSTEMS

Part 1ýConstructing the Platform
by Ed Sutter

Start ý The Typical Package ý What are the Alternatives? ý Key Ingredients ý MicroMonitor Run Time Startup ý Just After Reset ý Establish Exception Handlers ý I/O Initialization ý Flash Memory Drivers ý Sources and PDF

I/O INITIALIZATION

At this point, you have the basic initialization completed and are at C level. The monitor has initialized memory and stack, and it can access its periphery without having any kind of bus error. Even if it did have a bus error, you would be able to handle it through some exception handler. Now, make sure that all peripherals are settled down, reset and disable all I/O, and initialize the UART. (If you have anything to say about it during the hardware design, try to make sure that the microprocessor has the ability to reset each of its peripherals independently, without the need to power-cycle or hard-reset the target. This comes in handy.) This should always be the first device (after memory) to be configured so that you can start to use printf() to report status to the user.

The UART functions provide a raw putchar(), getchar(), and gotachar() for use throughout the monitor code. Each function is written in Polled mode, and a hook is provided within the function so that an alternate function can be called in its place. This alternate function is typically a function that is part of an operating system and is provided so that the monitor functions, which call putchar(), getchar(), and gotachar(), can still be used by an application that runs on top of the monitor and has reinitialized the UART to run under its domain. An example implementation for getchar() with the hook can be seen in Listing 3.

By default the remotegetchar function pointer is null, so the local code to retrieve a character would be executed.

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