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USING A BOOT MONITOR IN EMBEDDED SYSTEMS

Part 2ıBuilding on the Basics
by Ed Sutter

Start ı The Ethernet Interface ı The Command Line Interface ı "Get Your Tokens Here" ı One Last Topic About CLI ı Executable Scripts ı Application-to-Monitor Hook-Up ı The Moncom() Function ı The Monconnect() Function ı Letıs Regroup ı Xmodem and Tftp ı OK, Iım Done! ı Sources and PDF

In last monthıs article, we initialized the UART for printf(), the exception handlers in place, and basic flash interfaces initialized. This month, letıs do some miscellaneous initialization of basic monitor facilities like the command line history buffer, malloc()ıs heap space structures, shell variable storage, and file system control structures.

At this point, you can assume that the basic system is initialized. Most of what I showed you in Part 1 is typical for a monitor. But, from this point on, letıs assume the existence of files, both data and executable, so we can start breaking away from just being a simple boot monitor. You can now overlay a format on the section of flash memory thatıs to be allocated to the tiny flash file system (TFS).

TFS is a linear file storage system that provides an embedded system with the ability to treat flash memory as name space instead of address space. After the code accesses the flash memory as internally organized names, a whole new level of functionality becomes available to the monitor. [1]

First, the monitor looks to this flash space to see if it can make any sense of it. If not, then you are alerted that the file system is corrupted and it must be cleaned up. If there is a valid set of files, then the monitor looks for a file called monrc (run control file for the monitor). If this file is found, it is automatically run as an executable file. For now, use it for what it was originally intended for, to establish an IP, gateway, network mask, and MAC address for the target. This is done by setting some shell variables (IPADD, GIPADD, ETHERADD, and NETMASK, respectively). Listing 1 is an example monrc file for setting sell variables.

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Notice that Listing 1 is a script, not a binary executable. This is the first of several features that become available through TFS. This monrc file simply executes the monitor command set four times, and the result is that those four shell variables are initialized and now accessible to other portions of monitor code. For the immediate case, the monitor uses these variables for initializing the Ethernet driver.

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