### System Monitors / Freezer

There are a lot of pure software freezers out there. The usage of such tools may be of great help during the development and debugging of Slaves and the installed program. WHDLoad directly supports HRTmon and ThrillKill. Other kinds may be used via the option NoTrapHandler/S (this has some other disadvantages of course). If you want direct support for an other one, you can contact me and if it can be done, I will include support for it. On the startup of WHDLoad it will check if one of the supported monitors are active. If one is found WHDLoad will do some special stuff. If the MMU is used by WHDLoad it will declare the memory used by the monitor as valid and WriteThrough cacheable. During the game/demo runs it will forward all NMI exceptions to the NMI vector saved from the monitors vector table. Additional, if the VBR is moved by WHDLoad (NoVBRMove/S is not set and the cpu is at least a 68010) it will compare the FreezeKey with the actual keyboard value at each interrupt. If the values matchs WHDLoad will do the required keyboard stuff, transform the stackframe to a NMI stackframe and enter the monitor via his NMI handler.

#### HRTmon

The detection in memory should be relative safe. I think it will also work with future versions. Be careful if the MMU is used by WHDLoad: don't access area outside BaseMem from HRTmon. It will crash because HRTmon does not handle the resulting Access Fault Exception.

In the HRTmonPrefs you must check the 'No VBR move' box, otherwise you will not be able to enter the monitor while WHDLoad is running.

After returning from an activated HRTmon to the program running under WHDLoad you may note a incorrect graphic display. This is because HRTmon overwrites some custom register. You can work around this by telling HRTmon the correct value, e.g. use `'e $100 $5200'` for a 32 color screen before return.

The HRTmon built into WinUAE can only be detected if HRTmon has been previousy activated at least one time (press key PgUp). Because on first activation the NMI vector will be set which is used by WHDLoad to locate the monitor.

#### ThrillKill

There is no useable signature in the freezer, so some code compares are used. Therefore the detection will not work with other versions.