Atari 130XE Uživatelský manuál stáhnout pdf (Strana 28)

3 Debugger and DOS

DISK FULL

The disk is full

FILE LOCKED

The ﬁle is locked

DIRECTORY FULL

The directory is full (at most 64 ﬁles per disk)

3.2 Debugger

A debugger is used by machine language programmers to display, alter and improve object

code and other memory contents directly in the computer memory. Doing this in the

environment of a freezer brings certain advantages. Because of the way the freezer works,

there are also some limitations that may be circumvented by using the right procedures.

3.2.1 Access to memory and hardware registers

Without a doubt, the biggest advantage is the possibility to work with the frozen system

state. Doing this creates the impression of having a second computer, that’s linked into

the ﬁrst, stopped Atari. It enables you to “look into” and change the stopped Atari and

to resume any time. A debugger without freezer always has severe problems because of

its own memory usage and because the I/O operations of the debugger itself change the

system state. A programmers’ term for this is “trashing”, meaning turning the content of

the system into “trash”.

A standard debugger requires RAM for its own operation and will trash the data that

was put there by the program that’s being looked at. And even if the debugger is more

sophisticated (and comes with its own RAM), it will still trash the hardware registers of

ANTIC, POKEY and GTIA. There are no OS shadow registers for player missile graphics

and sound registers and the existing OS shadow register will be deactivated by many

programs anyway. As a result of the trashed hardware registers, it will be a lot of work,

if even possible, to resume a program. And apart from this, debuggers without a freezer

don’t have the ability to display the content of the non-readable (write-only) hardware

registers. So even if the register contents are not trashed by the debugger, the values in

the registers remain unknown.

Using the built-in debugger of the

TURBO FREEZER

, all information about the system

state is available. The contents of the hardware registers (i.e. what has been written there,

not the status returned by a read operation) can be viewed in the I/O area and may be

changed, without having to fear a system crash. The changes are applied only to the

frozen program. You can work with the complete RAM area (even the RAM under the

OS ROM), without trashing or fearing a crash.

In addition, there are various advantages resulting from running in the environment

of the

TURBO FREEZER

. The load and save functions and the DOS functions allow

for instantaneous testing and retrying, without lengthily reloading a program. And if

the change works not as expected, it may be undone instantly without problems. Using

this, even horrendous code monsters that overwrite parts of the DOS and that cannot be

processed in a simple way, are not frightening anymore.

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