wait for blitter vs immediate blitter

[jotd]

A500 quickstart configuration has "wait for blitter" set


I was testing with New Zealand Story (IPF) which has blitter bugs in the walrus kidnapping intro before game starts (that we fixed in the whdload slave)


But with A500 quickstart & wait for blitter the blitter bugs are still here. Switching to "immediate blitter" fixes the issue, but I'm now wondering what is the difference between wait for blitter and immediate blitter, and if wait for blitter isn't per chance broken (I saw the issue with other games too under whdload while fixing blitterwaits)

[Rotareneg]

The full compatibility A500 quickstart, which enables cycle-exact mode, doesn't have wait for blitter set (and can't use immedate blitter.) If you turn the comparability slider down it turns off cycle exact and enables wait for blitter.

Originally Posted by Toni Wilen

"Wait for blitter" works like normal unless CPU attempts to access blitter registers while previous blit is still active. In this case it temporarily halts the CPU and releases it when previous blit has finished.

In that thread there's more discussion about it. Immediate blitter on the other hand seems performs the blitter operation without any simulated delays, so that as far as the emulation is concerned the blitter performs its work instantaneously and is thus always ready for another blit, regardless of how fast the emulated CPU may be running from JIT, etc.