Fiddle with comments in mmss.s, save 2 bytes.

1 files changed, 31 insertions, 17 deletions

diff --git a/mmss.s b/mmss.s
index f1423b5..de60485 100644
--- a/mmss.s
+++ b/mmss.s
@@ -1,8 +1,19 @@
 
+;;; Subroutine: print_mmss
+;;; Print the 3-byte jiffy count at cloksav as minute/seconds/centisec.
+;;;
+;;; Will print up to 10 characters using printchr. Normally it's only 8,
+;;; because normally, the number of minutes is less than 100, even if
+;;; the user unwisely enters a 5-digit particle count.
+;;;
+;;; Uses the floating point ROM routines, because it's easier to code
+;;; this way (or so I thought!), and we don't need speed here.
+;;;
+;;; Caller must define cloksav (3 bytes), fptmp (6 bytes), and tmp1
+;;; (1 byte). These don't absolutely have to be in zero page, but
+;;; it's nice if they are.
+;;;
 print_mmss:
-; calculate and print elapsed time
-; uses the floating point ROM routines, because it's easier to code
-; this way and we don't need speed here.
  ldx #0    ; low byte of 256 (0)
  stx FR0
  inx
@@ -30,16 +41,13 @@ print_mmss:
  jsr IFP  ; ...ok, now:
  jsr FADD ; add the high bytes in jiffies, result in FR0 again
 
- ; copy to fptmp before dividing (we need it later)
+ ; at this point, FR0 holds the 24-bit jiffy count, converted to FP.
+ ; copy to fptmp before dividing (we need it later).
  ldx #<fptmp
  ldy #>fptmp
  jsr FST0R
 
- ; we now have the 3-byte jiffy count in FR0 and fptmp.
  ; 3600 NTSC jiffies or 3000 PAL jiffies = 1 minute, so divide.
- ; floating point constants:
- ; 3600.0 is $41,$36,$00,$00,$00,$00
- ; 3000.0 is $41,$30,$00,$00,$00,$00
  jsr load_jpm_fr1
 
  jsr FDIV  ; FR0 = FR0 / FR1 (and FR1 is now garbage)
@@ -64,6 +72,7 @@ truncloop:
 truncdone:
 
  ; print digits in FR0
+ ; don't use FASC, easier to do it this way.
  lda FR0
  and #$03
  sta tmp1
@@ -81,6 +90,8 @@ floopdone:
  lda #':'
  jsr printchr
 
+ ; we don't have a modulus or remainder operation in the ROM, so
+ ; handroll one here.
  ; multiplication and division trash FR1, which is annoying.
  jsr load_jpm_fr1
  jsr FMUL
@@ -95,7 +106,7 @@ floopdone:
  jsr FSUB
 
  ; load 0.6 into FR1 so we can divide by it.
- ; result will be number of centisec.
+ ; result will be number of centisec (e.g. 1050 for 10.5 sec).
  jsr zero_fr1
  lda #$3f
  sta FR1
@@ -110,6 +121,7 @@ floopdone:
  ; FR0 has division result, which is centiseconds.
  ; if the exponent is 0, we're OK. otherwise, shift down
  ; one byte so we print 00 for the seconds.
+ ; again, avoid FASC.
  lda FR0
  and #$0f
  bne twodigits
@@ -123,18 +135,19 @@ twodigits:
  lda #'.'
  jsr printchr
  lda FR0+2
- jsr printhex
-
- rts
+ jmp printhex
 
 ; load jiffies-per-minute into FR1. needs done twice so
 ; it's a subroutine.
+; floating point constants:
+; 3600.0 is $41,$36,$00,$00,$00,$00
+; 3000.0 is $41,$30,$00,$00,$00,$00
 load_jpm_fr1:
  jsr zero_fr1
  lda #$41 ; excess-64 base-100 exponent and sign (bit 7 = 0 means positive)
  sta FR1
  ldx #$36 ; 1st mantissa BCD byte, NTSC
- lda PAL
+ lda PAL  ; ask the GTIA what TV standard we're using
  and #$0e
  bne ntsc
  ldx #$30 ; 1st mantissa BCD byte, PAL
@@ -142,9 +155,10 @@ ntsc:
  stx FR1+1
  rts
 
-; ZF1 does *not* just clear out FR0, it uses the X reg as an 8-bit
-; pointer (to zero page only).
+;;; Subroutine: zero_fr1. Zeroes out all 6 bytes of FR1. Counterpart
+;;; to the OS's ZFR0.
+;;; Note: ZF1 does *not* just clear out FR1, it uses the X reg as an 8-bit
+;;; pointer (to zero page only).
 zero_fr1:
  ldx #FR1
- jsr ZF1
- rts
+ jmp ZF1