Page 84 - The Art of Designing Embedded Systems

Real Time Means Right Now! 71

-00432 03f80333 d88e MOV DS,BX
'-00431 03f80335 55 PUSH EBF
'CDEMON: 269 mme-led{ 1,
,-00430 03f80336 ffff62eB CALL NEAR PTR CS:-158
CDEMON' 355 void mme-led{ 1
1-00417 03f8029d 56 PUSH ESI
1-00415 03f8029e 57 PUSH ED1
&DEMON' 364 ; I c e: maskbi
:-00415 03f8029f be MOV ES1,SOO
E-00408 03f802a4 31 XOR DI,DI
eb JMP SHORT 41
83 CMP EDI.SO8
1-00402 03f802d4 d27c JL SHORT -46
CDEMON 366 led port[i++] = '1';
I 1-0039'3 03f 802a8 f9S9- MOV CX,DI

FIGURE 4-6 ISR trace collection on an emulator.

Are the triggers a pain to set up? Most emulators offer special menus
with dozens of trigger configuration options. Although this is essential for
finding the most obscure bugs, it is just too much work for the usual de-
bugging scenario, where you simply want to start collection when source
module line 124 executes. Simple triggers should be as convenient as
breakpoints, set perhaps via a right mouse click.
The moral is: trace is the right debugging tool, but keep ISRs simple.
Minimize their complexity to maximize their debuggability.

Easy ISR Debugging
What's the fastest way to debug an ISR?
Don't.
If your ISR is only 10 or 20 lines of code, debug by inspection. Don't
fire up all kinds of complex and unpredictable tools.
Keep the handler simple and short. If it fails to operate correctly, a
few minutes reading the code will usually uncover the problem.