[Amforth] Measuring time - timer for 1284p and Zero Drift Clock

[pito <pi...@vo...>]

..long time back.. maybe somebody finds it useful.. provided as-is..

Time measurement (with float results) 48bit timer (timer + epoch)
for 1284p:

\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\ 2007-12-26 EW   w4_clock_tick.fs
\ 2010-09-02 PITO - FLOAT TIME MEASUREMENT ATMEGA 1284P
\        +timer   register and enable interupt
\        -timer    disable interupt

marker -mytimer

2variable timer
variable epoch
1. 2constant _one
0. 2constant _zero
1 s>f fconstant f1.0

$B1 constant TCCR2B
$B6 constant ASSR
$70 constant TIMSK2
$016  constant TIMER2_OVFAddr

\ overflow2 interupt service routine
\ increment tick timer
: tick_isr
timer 2@ 
2dup 
_one d+ timer 2! 
0= if epoch @ 1+ epoch ! then ;


\ enable ticks
\ overflow fires each f_cpu/256/256
: +timer
$6 TCCR2B c! ( prescaler 110b = f_cpu/256 )
$0 ASSR  c! ( source: internal f_cpu)
['] tick_isr TIMER2_OVFAddr int! ( do register the interrupt )
0 epoch ! _zero timer 2!   ( clear the timer at start )
TIMSK2 c@  $01 or TIMSK2 c! ( do enable the timer2 interrupt ) ;

\ disable ticks
: -timer
TIMSK2 c@ $fe and TIMSK2 c! ( disable - clr timer2 interrupt ) ;

\ MEASURE TIME IN SECONDS (FLOAT)
decimal
2variable 0_ticks
\ tick_in_secs = 1 / f_cpu / 256 / 256
f_cpu d>f 256 s>f f/ 256 s>f f/ f1.0 fswap f/  fconstant
tick_in_secs
: timer-start ( -- ) timer 2@ 0_ticks 2! ;
: .elapsed (  -- ) timer 2@ 0_ticks 2@ d- d>f tick_in_secs f* 3 fsn.
." secs " ;

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and "zero drift clock" - it increments in one second interval - when
you know the exact crystal frequency (ie f_cpu = 12.487.388 Hz) then
you get a precise second - none other tweaking required

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marker _zerodriftclock_

\ ZERO DRIFT CLOCK 
\ IT USES F_CPU ONLY (XTAL FREQUENCY SHALL BE KNOWN AS PRECISE AS \
POSSIBLE) FOR PRECISE 1 SECOND INCREMENT
\ IT WORKS WITH _ANY_ VALUE XTAL
\ THE SECONDS ARE INCREMENTED IN 1 SEC INTERVAL
\ USES TIMER2 ATMEGA32
\ Pito July2010

decimal

2variable ticker
variable seconds

262144. 2constant clkpi    ( clk per interrupt = 256*prescaler )
1. ticker 2!
0 seconds !

\ overflow2 interupt service routine
\ ! not optimised yet
: tick_isr
ticker 2@ clkpi d- ticker 2!
ticker 2@ clkpi d< if  f_cpu ticker 2@ d+ ticker 2!
1 seconds +!
then ;

hex
\ enable ticks
: +ticks
7 TCCR2 c! ( 111b = f_cpu clock/1024 )
0 ASSR  c! ( source: internal clock f_cpu)
['] tick_isr TIMER2_OVFAddr int! ( register interupt )
TIMSK c@ 40 or TIMSK c! ( enable timer2 interupt ) ;

\ disable ticks
: -ticks
TIMSK c@
[ 40 invert ff and ] literal and TIMSK c! ( clr timer2 ) ;

decimal
: shwticker 1000 0 do cr ticker 2@ d. space seconds @ u. loop ;
: shwsec seconds @ u. ;
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p.

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