Motorola M5271EVB, Руководство пользователя

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3-2 M5271EVB User’s Manual
What Is dBUG?
Most commands can be recognized by using an abbreviated name. For instance, entering
“h” is the same as entering “help”. Thus, it is not necessary to type the entire command
name.
The commands DI, GO, MD, STEP and TRACE are used repeatedly when debugging.
dBUG recognizes this and allows for repeated execution of these commands with minimal
typing. After a command is entered, simply press <RETURN> or <ENTER> to invoke the
command again. The command is executed as if no command line parameters were
provided.
An additional function called the "System Call" allows the user program to utilize various
routines within dBUG. The System Call is discussed at the end of this chapter.
The operational mode of dBUG is demonstrated in Figure 3-1. After the system
initialization, the board waits for a command-line input from the user terminal. When a
proper command is entered, the operation continues in one of the two basic modes. If the
command causes execution of the user program, the dBUG firmware may or may not be
re-entered, at the discretion of the user’s program. For the alternate case, the command will
be executed under control of the dBUG firmware, and after command completion, the
system returns to command entry mode.
During command execution, additional user input may be required depending on the
command function.
For commands that accept an optional <width> to modify the memory access size, the valid
values are:
• B 8-bit (byte) access
• W 16-bit (word) access
• L 32-bit (long) access
When no <width> option is provided, the default width is.W, 16-bit.
The core ColdFire® register set is maintained by dBUG. These are listed below:
• A0-A7
• D0-D7
• PC
• SR
All control registers on ColdFire® are not readable by the supervisor-programming model,
and thus not accessible via dBUG. User code may change these registers, but caution must
be exercised as changes may render dBUG inoperable.
A reference to “SP” (stack pointer) actually refers to general purpose address register
seven, “A7.”