Hmm. Well, it does seem to suggest that, and if I hadn't just found out otherwise from my tests, I'd be inclined to agree with you. I can't speak for other processors personally, since I don't really have any experience coding to the metal on any other systems.If you read further:
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It is clearly stated that acknowledge cycle only occur when the interrupt is not masked, and this seems logical to me, it is how most processors are working...
Actually, VMA isn't used for interrupt processing, and isn't connected in the Mega Drive. Interrupts are acknowledged through the normal signal lines. Section 5.1.4 in the M68000 Users Manual shows an interrupt acknowledge cycle.VDP requests automatic vectoring, that means that the VDP set /VPA and wait for acknowledge trough /VMA from the 68000.
EDIT: From looking more closely, it looks like it's really the chip which signalled the interrupt which terminates the interrupt acknowledge cycle, either by asserting VPA or DTACK. Once the external chip signals either VPA or DTACK, it doesn't get another signal, so technically, there is no "INTAK" line normally. In the Mega Drive, they created an INTAK because the VDP doesn't directly assert VPA. The Bus Arbiter is the only chip which connects to the FC lines (to detect when an interrupt acknowledge cycle is running), and the VPA line (to autovector an interrupt). It then has an INTAK line running to the VDP, which the bus arbiter asserts to tell the VDP when it has completed the interrupt acknowledge cycle. It probably asserts this line in tandem with VPA.
Well I guess that explains my problems with Lemmings then.What is sure is that HINT (Level 4) remains pending as long as it is not acknowledged and enabled through VDP register, some games (Lemmings, and maybe Wiz 'n Liz for example) won't work properly without this being emulated...