USING A BOOT MONITOR IN EMBEDDED SYSTEMS

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USING A BOOT MONITOR IN EMBEDDED SYSTEMS

Lessons from the Trenches 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

THE MONCONNECT() FUNCTION

So, the application knows where this moncom() function is in monitor space because a pointer to this function is stored in a well-known address. Now, other functions in application space can use this function to "connect" the application to the monitor. This is where monConnect() comes in. This function takes as one of its arguments the well-known address shown in Listing 12.

Both the moncom() function in the monitor and the monConnect() function in the application compile with the same monlib.h file. This header file contains all of the GETMONFUNC_XXX definitions. The application calls monConnect and this connects the function pointers _rputchar, _getchar, and _gotachar to the corresponding rputchar, getchar, and gotachar functions in the monitorıs space. At this point, the application could just use those function pointers, however, it would be nicer for the application to have functions (not pointers) to access the monitor code. This allows the function to wrap the monitor access with a semaphore or some other lockout mechanism, prior to entering monitor code space. This also provides protection to the monitor because it might be used in a multitasking environment.

Listing 13 is the code in the application space that can be used to call the monitor for rputchar. All of the mon_ interface functions are similar.

int
mon_putchar(unsigned char c)
{
int ret;

if (_monlock)
_monlock();
ret = _rputchar(c);
if (_monunlock)

_monunlock();
return(ret);
}

Listing 13ıThis code can be used to call the monitor for rputchar.

The monitor lockout functions are optional and would be set up using the second and third arguments of the monConnect function.

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