[Amforth-devel] Interesting phenomenon

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

Hi,
thanks to Matthias the anycrystal clock works! However, I can
observe an interesting phenomenon I do not understand:
1. when I fresh flash atmega and upload the clock:

\ count clock 1 second ticks from timer2 overflows:
\ any crystal clock

2variable ticker
2variable seconds
262144. 2constant clkpi
1. 2constant d_one1

0. seconds 2!
1. ticker 2!

decimal
\ overflow2 interupt service routine
\ increment tick
: tick_isr
ticker 2@ clkpi d- ticker 2!
ticker 2@ clkpi d< if f_cpu ticker 2@ d+ ticker 2! 
seconds 2@ d_one1 d+ seconds 2!
then
;

hex
\ enable ticks
: +ticks
7 TCCR2 c! ( 111 = 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 Timer 2 )
;
decimal

2. then after first usage of +ticks the second increments by 10 -
the clock tick is 10HZ, so the inerrupt runs 10x faster, or
something like that !!??!!

3. when I unmark the clock routine and upload it again (no change in
code, no flashing of atmega) the clock works fine - 1 second tick,
increment by one per second.

Any idea? Pito.