C0 has plenty of room. A big block of free space starts at C0/D613 and ends at C0/DF9F. I do have a couple of patches towards the beginning of that space, but they are patches that need serious re-working.
As for your fix, how about something like this?
org $C31566
XBA
LDA $00
XBA
ASL A
REP #$20
LDX #$07FE ; start from the end of the buffer, and work our way down
branch:
STZ $0867,X
DEX
DEX ; since we're doing 2 bytes at a time, this will use fewer cycles, and less space
BPL branch
TAX ; back to our original code to load from SRAM to working SRAM
LDA $C3155E,X
TAX
SEP #$20
LDY $00
branch2:
LDA $306000,X
STA $1600,Y
INX
INY
CPY #$0A00
BNE branch2
RTSThat would use only 11 bytes of free space. I'm not entirely sure I clear the last byte of the buffer, though.
