Texas Instruments CDT370, User Manual

Page: 38 / 83

Trace and Timing
3-2
3.1 Trace and Timing
There is a 2K x 16-bit trace circular buffer on the CDT370 board. The TMS370
internal address bus is stored each time an opcode fetch is detected. When
you want to display the contents of this buffer, the debugger reconstitutes all
the opcodes executed by the TMS370.
This trace feature is fully real time because the CPU is not halted. The sample
capture begins when you start the CPU and ends when you halt it, either with
a breakpoint or halt command.
A 24-bit-wide on-board counter is incremented by the CPU’s clock, so the total
number of cycles can be measured between two defined instructions (refer-
enced by two breakpoints).
The capacity of this counter is up to 16 777 216 cycles; at 20 MHz, that means
a total time of 3.35 seconds.
Trace Feature
The trace feature is used to display trace samples that have been collected,
as well as the value of the timer.
When you select Trace from the menu bar, a pull-down menu is opened, where
you can open the Inspect window, position the frame to display within the In-
spect window, or save the trace buffer to a file.
Most of the inspect window consists of space for the trace samples. In the bot-
tom corner, the value of the on-board timer is displayed. You can move and
scroll through trace samples in the same way as with other windows.
Trace Samples
Trace samples are snapshots of bus cycle activity that are collected and stored
by the on-board trace logic when the CDT370 is running.
The trace buffer is a circular buffer that can hold 2048 samples. If more sam-
ples than this are collected, the buffer wraps around, and new samples over-
write the old ones. Each sample is 16 bits wide and contains the value of the
address bus of the CPU when an opcode fetch is detected.
Each trace sample is referred to by its index in the trace buffer, starting from
0. Trace samples with lower indices are chronologically older than samples
with higher indices. Thus, if the buffer is full, sample 2046 is always the most
recent sample taken.