Galway collection, part 1

MARTIN GALWAY COLLECTION, PART 1 SID music player for eLeMeNt ZX and MB03+ rev 2===============================================================================Four pieces by Martin Galway, played by his own 6502 driver rewritten for theZ80. The music data is untouched - what you hear should be the original oldbytecode interpreted note for note. However, the player is still unfinishedand experimental. 1 Loader (Rambo) Ocean 1985, the loading music (with the Morse message Galway put in it) 2 Green Beret Konami / Imagine 1986 3 Wizball 1 Ocean 1987 4 Wizball 2 Ocean 1987, the enter-your-name tune KEYS------------------------------------------------------------------------------- 1 - 4 play that tune from the beginning; pressing it again restarts it SPACE stop ENTER pause; then any key carries on and SPACE gives up instead -> right arrow (CAPS + 8) scrubs forward, and keeps going for as long as you hold it. V the bars on or off. The channel names and the figures beside them stay either way, so it is still plain which voice is playing and what it is doing; L loop on or off. With it off - which is how it starts - each tune plays through once and the list comes back. S 6581 or 8580 - which SID the player pretends to talk to. The two chips filter quite differently (Wizball's long filtered intro is the place to hear it). N / P NTSC or PAL - how fast the SID itself is clocked, which sets the pitch. None: Wizball has a frequency table for each and gets the matching one. Green Beret and Rambo carry only one table, computed for a 1 MHz clock, so with N they are in tune the way the numbers were meant and with P they sit about two thirds of a semitone lower - which is how they sounded on the European machines. Try both and use the one you like. A B C silence voice 1, 2 or 3; press again to bring it back. Each bar is labelled with the key it answers to. Starting a tune turns everything back on. F the same for the filter - the voices carry on but stop being routed through it, which is the quickest way to hear what it was doing. T time base - where the player takes its timing from. Three settings, see below. PAL, NTSC AND WHY IT IS NOT ABOUT SPEED-------------------------------------------------------------------------------Two things differed between a European and an American C64, and they are easyto mix up.The SID was clocked a little faster over there, and since the pitch of a notecomes from that clock, the same numbers would sound higher. So a tune needs adifferent frequency table for each - which is why Galway wrote two of them forWizball and marked them P.A.L. and N.T.S.C.And the picture ran at 60 frames a second instead of 50. The driver is calledonce per frame, so the same tune simply played a fifth faster over there. Thathas nothing to do with the tables; it is the tempo.Here the frame is always the ZX Spectrum's 50 Hz, so what you hear is alwaysthe European tempo. N and P change the pitch only, never the speed - and thereis nothing to be done about the tempo short of rewriting the music. TIME BASE-------------------------------------------------------------------------------The music runs four times per frame - once per frame for the two older tunes -so something has to say when a frame has gone by and when each quarter of ithas. This is a different thing again: it is how finely the envelopes and thevibrato are updated inside a frame, not which country the tune is from. Tcycles through three ways of doing that. All three should sound very similar;they differ in what they rely on. counted delay loop Counts instructions. The player measures how many fit in one frame at start-up, so it works at any CPU speed, but it is the least precise of the three. raster, ZXi beam line Reads the beam position from the ZXi register and waits for quarter-frame lines - the same idea as the original on the C64, which timed itself off the raster. ZXi 48bit counter Reads the machine's clock counter. It cares neither about the CPU speed nor about the video, so it is the steadiest of the three.Both counters are measured at start-up rather than assumed. If one of them doesnot behave, the line says "no beam" or "no clock", that setting quietly fallsback to the delay loop, and a row of numbers appears showing what was measured.On working hardware you will never see it.-------------------------------------------------------------------------------Music (C) Martin Galway / Ocean Software, 1985-87 Z80 port: samista and Zirin