save 12 more bytes, 7368 free, document the hell out of console.s

1 files changed, 26 insertions, 1 deletions

diff --git a/console.s b/console.s
index 7837ce1..1930303 100644
--- a/console.s
+++ b/console.s
@@ -138,7 +138,32 @@ _rvs_off:
  ; ...or 5 bytes each. we have 5 of them, so 25 bytes. using fall-thru
  ; and the BIT trick, they condense down to 17 bytes.
  ; if you're not familiar with the "BIT trick" to skip a 2-byte instruction,
- ; the stuff below looks like gibberish, sorry.
+ ; the stuff below looks like gibberish... here's a mini-tutorial:
+
+ ;store1:
+ ; lda #1
+ ; .byte $2c ; this is the opcode for BIT absolute
+ ;store2:
+ ; lda #2
+ ; sta $0600
+ ; rts
+
+ ; if entered via "jsr store1", the above code fragment executes these
+ ; instructions:
+ ; lda #1
+ ; bit $02A9 ; $A9 is the LDA immediate opcode, 02 is the #2
+ ; sta $0600
+ ; rts
+
+ ; if entered via "jsr store2", it's
+ ; lda #2
+ ; sta $0600
+ ; rts
+
+ ; the "bit $02a9' doesn't affect any registers other than the flags,
+ ; and the "sta $0600 : rts" part doesn't depend on any of the flags,
+ ; so the BIT is effectively a no-op that "masks" the 2-byte LDA #2
+ ; instruction "hidden" as its operand.
 
  ; ", Taipan? "
  ; using fall-thru here saves 3 bytes (normally the last instruction