[msdos386] How to switch to to real mode and back to protected in order to be able to switch to VGA bitmap mode? Any alternative to real mode?

[Fabrizio-Caruso]

My VGA Assembly code for the msdos86 works fine on the msdos86 and pc86 targets but not on the msdos386.

I suppose I need to be in real mode in order to be able to use interrupts which I need to set up VGA mode and also handle the keyboard input.

I have not found a way to set VGA mode without real mode interrupts.

If you know of an alternative/better/simpler way to switch to VGA bitmap mode, I may consider it.

[davidgiven]

Yes, there's code for this. Instead of just calling int 0x21 (or whichever interrupt), do a callf (interrupt_ptr) with the interrupt number in the high half of ebx. See:

https://github.com/davidgiven/ack/blob/default/plat/msdos386/libsys/sys_dpmidos.s

[Fabrizio-Caruso]

Not sure I understand what I need to do with the registers that are used as parameters.
How do I translate? 0x10 goes into the high byte of ebx but what about 0x13 that was going to ax? does it go into the high byte of eax?

    mov ax, 0x13
    int 0x10

[davidgiven]

Values in the low halves of the registers are passed through unchanged to the DOS interrupt (which is why the interrupt number has to go in the high half of a register, because it was the only space left).