Atmos ROM1.1b timer restoration disassembly
ROM SHA256 ed28568574716eef5d7c0fde2568d7a47a6e4b1fbca81daff3be05e45723466d

E93D  20 f5 e5    JSR $e5f5
E940  20 aa f9    JSR $f9aa
E943  4c e0 ed    JMP $ede0

EDE0  48          PHA
EDE1  20 8c ee    JSR $ee8c
EDE4  a9 00       LDA #$00
EDE6  a2 00       LDX #$00
EDE8  a0 03       LDY #$03
EDEA  20 ab ee    JSR $eeab
EDED  a9 01       LDA #$01
EDEF  a0 19       LDY #$19
EDF1  20 ab ee    JSR $eeab
EDF4  a9 00       LDA #$00
EDF6  8d 71 02    STA $0271
EDF9  ad 0b 03    LDA $030b
EDFC  29 7f       AND #$7f
EDFE  09 40       ORA #$40
EE00  8d 0b 03    STA $030b
EE03  a9 c0       LDA #$c0
EE05  8d 0e 03    STA $030e
EE08  a9 10       LDA #$10
EE0A  8d 06 03    STA $0306
EE0D  8d 04 03    STA $0304
EE10  a9 27       LDA #$27
EE12  8d 07 03    STA $0307
EE15  8d 05 03    STA $0305
EE18  68          PLA
EE19  60          RTS

Conclusion: E93D restores VIA and jumps EDE0, which writes timer1 low=$10 high=$27, period10000 cycles.
The game calls _InitIRQ (20000 cycles) before loading sprites, then sprites+caves load invoke E93D and restore10000 cycles.
At1MHz original runtime IRQ cadence therefore100Hz; theme note16 countdown plus onset tick=17 ticks=0.17seconds.
This explains native reference AVI title music note intervals and does not involve2x CPU/AY clock or a capture bug.
