\ Program Name: timer.fs
\ Date: 2016
\ Copyright 2017  t.porter <terry@tjporter.com.au>, licensed under the GPL
\ For Mecrisp-Stellaris by Matthias Koch
\ Chip: STM32F051
\ Board: STM32F0 Discovery Board
\ Terminal: e4thcom, Copyright (C) 2013-2017 Manfred Mahlow (GPL'd)  https://wiki.forth-ev.de/doku.php/en:projects:e4thcom
\ Clock: 8 Mhz using the internal STM32F051 RC clock, unless otherwise stated
\ All register names are CMSIS-SVD compliant
\ Note: gpio a,b,c,d,e, and uart1 are enabled by Mecrisp-Stellaris core as default.
\
\ This Program : 
\ * measures elapsed time using the SYSTICK.
\ * Flashes the BLUE led every second by counting 1000 systicks
\ * A 1mS marker pulse is available on PB2
\
\ Registers Used:- As defined below
\ timer.fs is self contained, no other files are required
\ To be done: modify the code to run from Flash after a reboot.
\ ------------------------------------------------------------------------------------------------------

 \ Define Systick memory mapping as its not in CMSIS-SVD
 $E000E010 constant STK_CSR	\ SysTick control and status register. R/W reset value = $00000000
 $E000E014 constant STK_RVR	\ SysTick reload value register. R/W reset value = 6000 (6MHz clock) for the STM32F0
 $E000E018 constant STK_CVR	\ SysTick current value register. R/W value unknown  
 $E000E01C constant STK_CALIB	\ SysTick calibration value register. Read Only, $40001770 for the STM32F0
 \ Define other regs
 $48000400 constant GPIOB_MODER ( GPIO port mode register )
 $48000800 constant GPIOC_MODER ( GPIO port mode register )
 $48000418 constant GPIOB_BSRR  ( GPIO port bit set/reset  register )
 $48000814 constant GPIOC_ODR

\ Variables
 0 variable second_counter
 0 variable ms_counter		\ can count to 32 bits or -> $ffffffff u. =  4294967295 mS or 4294967 seconds, or 71582 minutes or 1193 hours.

 : INIT-SYSTICK
 %01 4 lshift GPIOB_MODER bis!	    \  set PB2 to push pull output for the Marker
 %01 8 2* lshift GPIOC_MODER bis!   \ PC8 as output for F0 Disco LED
 8080 STK_RVR !			    \ systick calib for 1ms using internal 8mhz osc
 %101 STK_CSR bis!		    \ systick enable
 ;

 : marker-set			    \ 1mS pulse for scope at PB2
 %1 2 lshift GPIOB_BSRR bis!	    \ set PB2 = 1
 ;

 : marker-clear
 %1 18 lshift GPIOB_BSRR bis!      \ clear PB2
 ;

 : toggle-systick-led
    GPIOC_ODR @
    1 8 lshift xor
    GPIOC_ODR !
 ;

 : systick-handler
 marker-set
 ms_counter @
 1+
 ms_counter !
 second_counter @
 1+			    \ add one to the counter
 dup
 1000 >= if		    \ If counter is > = 1000 ...
 toggle-systick-led	    \ blink the LED at 1s rate
 drop			    \ drop the counter value of 1000  from the stack
 0			    \ put 0 on the stack to load in the counter after the 'then'
 then
 second_counter !	    \ reset the counter to zero
 marker-clear
 ;

 ' systick-handler irq-systick !    \ This 'hooks' the systick-handler word (above) to the systick irq
 ENABLE-SYSTICK-INTERRUPT	    \ enable it last


 : delay ( delay-value -- elapsed-time )				    
 0 ms_counter !			    \ reset the ms_counter to zero
 0 DO LOOP			    \ the simple delay loop to be timed
 ." = "
 ms_counter @ .			    \ this will be updated by the systick-handler every systick and we just read it when the delay finishes
 ." milliseconds " cr
 ;

 INIT-SYSTICK


\ ~~~~~~~~~~ Screenshots ~~~~~~~~~~~~
\ 10000 delay = 6 milliseconds
\ 1000000 delay = 625 milliseconds
\ 10000000 delay = 6256 milliseconds