Hey, all.  Adam here.

I was curious about reserve missiles, and Kejardon's RAMMap.txt said that it's
only used by 91:DF80, so I disassembled it.

The full disassembly is below, because I want to put my explanation first.

When you get a missile pickup dropped by a slain enemy, the missile pickup
routine is called with the size of a pickup in A.  That size gets added to
Samus' current missile stock.  If she isn't fully stocked yet, we're done: we
just restore registers and RTL.

If this pickup pushes her over her *max* missiles, though, the overflow gets
added to her *reserve* missiles.  Her reserve missiles are limited to the
lesser of 99, and her max missiles.

Once max/reserve are set, current is set to max, and then the pull/RTL code
runs.  If we didn't skip down to that code in the first place, it was because
current is over max and the reserve-missile path was invoked.

There's still a lot of gameplay questions unanswered here--such as how the
player would see their reserve missiles and the mechanics of actually using
them--but I hope this is a fascinating glimpse of the cutting room floor.


$91/DF80 08          PHP
$91/DF81 8B          PHB
$91/DF82 4B          PHK
$91/DF83 AB          PLB
$91/DF84 C2 30       REP #$30
$91/DF86 18          CLC                    ; current += pickup_size
$91/DF87 6D C6 09    ADC $09C6  [$00:09C6]
$91/DF8A 8D C6 09    STA $09C6  [$00:09C6]
$91/DF8D CD C8 09    CMP $09C8  [$00:09C8]  ; if current <= max
$91/DF90 30 3E       BMI $3E    [$DFD0]     ;   goto out
$91/DF92 38          SEC                    ; overflow = current - max
$91/DF93 ED C8 09    SBC $09C8  [$00:09C8]
$91/DF96 85 12       STA $12    [$00:0012]
$91/DF98 AD C8 09    LDA $09C8  [$00:09C8]
$91/DF9B C9 63 00    CMP #$0063             ; if max <= 99
$91/DF9E 30 16       BMI $16    [$DFB6]     ;   goto add_until_max

; you might call this "add_until_99"
$91/DFA0 A5 12       LDA $12    [$00:0012]  ; reserves += overflow
$91/DFA2 18          CLC
$91/DFA3 6D D8 09    ADC $09D8  [$00:09D8]
$91/DFA6 8D D8 09    STA $09D8  [$00:09D8]
$91/DFA9 C9 63 00    CMP #$0063             ; if reserves <= 99
$91/DFAC 30 1C       BMI $1C    [$DFCA]     ;   goto reserves_ready
$91/DFAE A9 63 00    LDA #$0063             ; reserves = 99
$91/DFB1 8D D8 09    STA $09D8  [$00:09D8]
$91/DFB4 80 14       BRA $14    [$DFCA]     ; goto reserves_ready

add_until_max:
$91/DFB6 A5 12       LDA $12    [$00:0012]  ; reserves += overflow
$91/DFB8 18          CLC
$91/DFB9 6D D8 09    ADC $09D8  [$00:09D8]
$91/DFBC 8D D8 09    STA $09D8  [$00:09D8]
$91/DFBF CD C8 09    CMP $09C8  [$00:09C8]  ; if reserves <= max
$91/DFC2 30 06       BMI $06    [$DFCA]     ;   goto reserves_ready
$91/DFC4 AD C8 09    LDA $09C8  [$00:09C8]  ; reserves = max
$91/DFC7 8D D8 09    STA $09D8  [$00:09D8]

reserves_ready:
$91/DFCA AD C8 09    LDA $09C8  [$00:09C8]  ; current = max
$91/DFCD 8D C6 09    STA $09C6  [$00:09C6]

out:
$91/DFD0 AB          PLB
$91/DFD1 28          PLP
$91/DFD2 6B          RTL