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|
;;; 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) and fptmp (6 bytes).
;;; These don't absolutely have to be in zero page, but
;;; it's nice if they are.
;;;
print_mmss:
ldx #0 ; low byte of 256 (0)
stx FR0
inx
stx FR0+1 ; high byte of 256 (1)
jsr IFP ; FR0 now FP 256.0
jsr FMOVE ; FR1 = FR0 (both are 256.0)
jsr FMUL ; FR0 = FR0 * FR1 (65536.0) (and FR1 is now garbage, but...)
jsr FMOVE ; FR1 = FR0 (didn't need it anyway)
; cloksav is 3 bytes, MSB-first (like RTCLOK).
; first, convert the highest byte to jiffies:
ldx #0
stx FR0+1
lda cloksav
sta FR0
jsr IFP ; FR0 now cloksav in FP, FR1 = 65536.0
jsr FMUL ; FR0 = FR0 * FR1
jsr FMOVE ; FR1 = FR0, aka the high byte of cloksav in jiffies
; next, convert low 2 bytes of cloksav to FP...
lda cloksav+1
sta FR0+1
lda cloksav+2
sta FR0
jsr IFP ; ...ok, now:
jsr FADD ; add the high bytes in jiffies, result in FR0 again
; 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
; 3600 NTSC jiffies or 3000 PAL jiffies = 1 minute, so divide.
jsr load_jpm_fr1
jsr FDIV ; FR0 = FR0 / FR1 (and FR1 is now garbage)
; FR0 is now minutes elapsed (e.g. 1.5, for 90 sec). Only print the
; integer part...
; FP ROM has no equivalent to trunc(). You might think you could call
; FPI followed by IFP, but FPI rounds up (e.g. 1.5 comes out as 2,
; not 1). But it's not hard to do:
lda FR0 ; exponent
beq truncdone
and #$4f ; ignore sign
sec
sbc #$3f ; A gets either 1 or 2
tax
lda #0
truncloop:
sta FR0+1,x
inx
cpx #5
bne truncloop
truncdone:
; print digits in FR0
; don't use FASC, easier to do it this way.
; here we use the first byte of FR1 as a temp.
lda FR0
and #$03
sta FR1
inc FR1
ldx #0
floop:
lda FR0+1,x
jsr printhex
inx
cpx FR1
bcc floop
floopdone:
; done printing minutes, let's have the separator
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
jsr FMOVE
; reload original jiffy count into FR0
ldx #<fptmp
ldy #>fptmp
jsr FLD0R
; subtract FR1. FR0 ends up with jiffies modulo jiffies-per-sec.
jsr FSUB
; load 0.6 into FR1 so we can divide by it.
; result will be number of centisec (e.g. 1050 for 10.5 sec).
jsr zero_fr1
lda #$3f
sta FR1
lda #$60
sta FR1+1
jsr FDIV
; *now* we can actually make use of FPI's rounding!
jsr FPI
jsr IFP
; 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
lda FR0+1
sta FR0+2
lda #0
sta FR0+1
twodigits:
lda FR0+1
jsr printhex
lda #'.'
jsr printchr
lda FR0+2
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 ; ask the GTIA what TV standard we're using
and #$0e
bne ntsc
ldx #$30 ; 1st mantissa BCD byte, PAL
ntsc:
stx FR1+1
rts
;;; 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
jmp ZF1
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