Why wait a moment? (Optimization warning)
I'm not really sure. But I suspect the hardware not to react immediatly to changes in VIA registers/bits. VIA itself needs 1-2 cycles to initiate shifting and/or timing. Some things go through the MUX and others are negated along the way to their final destination (~RAMP/~ZERO). I experienced some timing problems optimizing Vectrex Frogger. I changed the above line routine to be a bit faster for my purposes. Since in Vectrex Frogger all 'sprites' are drawn using a scale factor of 6, which is the timer low counter, I thought that after 6 cycles from switching the timer on I could switch the light off, without a request loop, and the line would be drawn all right. This is not so. I think somewhere in the vectrex hardware there is a delay of a couple of cycles befor the signals reach their final destination (the integration hardware, in opposite to their first destination, the VIA registers/flags). And furthermore, that these delays are not the same for all operations, since everything would again be allright. I guess, for example, the ~RAMP enabling somehow takes more time than ~BLANK enabling. I have not done really many tests on that, perhaps some day I will. When optimizing vectrex programs keep this in mind and test timing critical routines carefully. There are some situations where you can easily change some registers to early, theoretically the results would be ok, but in reality vectrex will draw something weirdly different. The vector drawing and positioning routines have great potential for optimization, but be carefull!