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Function RTHaltCPL3

RTHaltCPL3 also waits for a hardware interrupt. However, unlike function RTHalt, it can switch to CPL 0 temporarily to execute the CPU HLT instruction:

BYTE RTHaltCPL3(void);

The function returns the current privilege level (0 or 3).

If the program runs at privilege level 0, HLT is executed. Otherwise, RTHaltCPL3 sets up a custom IDT, switches to ring 0 and executes HLT. When a hardware interrupt occurs, the function switches back to ring 3 and re-raises the interrupt to allow the application's handler to process the interrupt.

RTHaltCPL3 makes the advantages of the HLT instruction available without sacrificing protection. However, RTHaltCPL3 requires a privilege level transition before an interrupt is actually serviced. For example, on a Pentium 100MHz, using function RTHaltCPL3 would increase the interrupt latency by about 1 - 2 microseconds.

RTHaltCPL3 can also be used as an RTTarget-32 idle handler (see function RTWait). To have the Debug Monitor execute RTHaltCPL3 while it is idle, see the configuration file command COMPort.

Function RTHalt

Function RTWait