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Routines |
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Used by the routine at GamePlay_Start.
Plays a short chirp of seven square wave cycles. The period of each cycle depends on a counter, and on the value of FrameCounter.
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| PlayChirp | 6825 | LD C,$07 | Set the cycle counter to 07. | |
| PlayChirp_Loop | 6827 | LD A,C | Fetch the cycle counter. | |
| 6828 | DAA | Decimal adjust the counter, to vary the period of the cycle. | ||
| 6829 | XOR %11110000 | Flip bits 4-7. | ||
| 682B | RLCA | Rotate A left. | ||
| 682C | LD D,A | Put the result in D (the period). | ||
| 682D | LD A,($5F1D) | Fetch the frame counter. | ||
| 6830 | RRCA | Divide by 08 (rotating the bits). | ||
| 6831 | RRCA | |||
| 6832 | RRCA | |||
| 6833 | AND %01100000 | Keep only bits 5-6. | ||
| 6835 | XOR D | Combine with the period. | ||
| 6836 | LD D,A | Update the period. | ||
| 6837 | CALL PlaySquareWave | Play a cycle using PlaySquareWave. | ||
| 683A | DEC C | Decrease the cycle counter by one. | ||
| 683B | JR NZ,PlayChirp_Loop | Loop back to PlayChirp_Loop until the cycle counter is zero. | ||
| 683D | RET | Return. | ||
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