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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

LETıS REGROUP

The application starts up. It wants to use some of the facilities provided by the monitor, so assuming it knows the well-known address, it calls monConnect(). The monConnect() function is fed the well-known address and pointers to lock and unlock functions. The code in monConnect() now assumes that it can call moncom() in the monitor space through the well-known address. Each call to moncom() loads a function pointer in the application space with the address of the corresponding function in monitor space, based on the GETMONFUNC_XXX macro passed into moncom(). When monConnect() is done, there is a full set of mon_xxx (like mon_putchar()) functions in the application space that can now be used by the application to interface to facilities in the monitor. Note that there are a lot more than three functional connections established by monConnect(), but they are all basically done in the same way as the three shown in this example.

So where are you? Youıve got quite a bit, but without some way to transfer files and data to and from the target system, youıre still limited, hence the need for some file transfer capabilities. There are certainly plenty to choose from, but for the sake of a monitor, keeping it simple must continue to be the goalıyour RS-232 interface will support XMODEM and your Ethernet interface will run a TFTP server. Both will support transfers to and from RAM and the file system.

Donıt worry, I have no intention of discussing either of the protocols here; theyıve both been around long enough that you probably already have a book on your shelf that digs into it. The point is to briefly discuss some of the enhancements that Iıve added to each of them to work with the monitor. Both of these mechanisms download into RAM and then, if necessary, the data is transferred to TFS.

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