Page 192 - Embedded Microprocessor Systems Real World Design

I call these data outputs action codes. They are useful for debug and as a means
of correlating software execution with the real world as captured on a logic ana-
lyzer or digital storage oscilloscope (DSO) .
There are many ways to capture the action codes. They center around two basic
techniques: generating the data for hardware that may or may not be connected
and storing the information in memory for later retrieval. Both techniques have
advantages and drawbacks.

~~
Hardware Output

The hardware output technique depends on getting debug data (action codes) to
the outside world in some simple 8-bit, 16-bit, or even 32-bit format. Ideally, the
firmware will not check to see whether the debug hardware is connected. This is
because reliable debug depends on the firmware operating the same, regardless of
whether the debug hardware is connected. In the 8031 example mentioned earlier,
the processor used external read-only memory (ROM) and I/O ports. I connected

I/O DECODE
LOGIC
2:4 MULTIPLEXER
-- TO
-WR 0
-
- OTHER CIRCUITS
ADDRESS STROBE (CLOCKS ANALYZER)
LATCH
8051
A0 (INDICATES DATA NPE)

ADGAD7 (TRACE DATA)

NPICAL TRACE RESULT:
DATA A0
01 0 DEBUGDATA
02 0 DEBUGDATA
05 0 DEBUGDATA
80 0 DEBUGDATA
FF 1 MOTOR SPEED PARAMETER
7C 0 DEBUGDATA
21 1 MOTOR SPEED PARAMETER
59 0 DEBUGDATA
47 0 DEBUGDATA

Figure 6.1
Example of 8051 Trace Output Logic.

Adding Debug Hardware and Softuare 173