From fb8e8801a3a3a9907e3dfeba239c3f07eb3a8933 Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Mon, 31 Oct 2022 18:09:28 -0400
Subject: Print elapsed time in MM:SS.CC

---
 mmss.s | 150 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 150 insertions(+)
 create mode 100644 mmss.s

(limited to 'mmss.s')

diff --git a/mmss.s b/mmss.s
new file mode 100644
index 0000000..f1423b5
--- /dev/null
+++ b/mmss.s
@@ -0,0 +1,150 @@
+
+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
+ 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
+
+ ; 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)
+
+ ; 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
+ lda FR0
+ and #$03
+ sta tmp1
+ inc tmp1
+ ldx #0
+floop:
+ lda FR0+1,x
+ jsr printhex
+ inx
+ cpx tmp1
+ bcc floop
+
+floopdone:
+ ; done printing minutes, let's have the separator
+ lda #':'
+ jsr printchr
+
+ ; 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.
+ 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.
+ 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
+ jsr printhex
+
+ rts
+
+; load jiffies-per-minute into FR1. needs done twice so
+; it's a subroutine.
+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
+ and #$0e
+ bne ntsc
+ ldx #$30 ; 1st mantissa BCD byte, PAL
+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).
+zero_fr1:
+ ldx #FR1
+ jsr ZF1
+ rts
-- 
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