Electronic Circuits and Projects Forum

**Update: This is for the STM32F100RB Discovery Board**

The problem: For some reason the UIF (update interrupt flag) in the status register goes high before TIM6 overflows (reaches the value in the auto reload register).

When in debug mode, when I set a break point at the line indicated (then immediately hit continue when stopped) the status register behaves as it should (UIF does not go high until the timer overflows). At first I thought it might be a timing issue, but if I set a reasonably long delay before this line it still doesn't behave as expected.

Here is my code, in full:

Code :

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Timer - in ms	
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
;Directives
	PRESERVE8
	THUMB
 
;Constants
INITIAL_MSP	EQU	0x20002000	;initial main stack pointer
 
;TIM6
TIM6_CR1	        EQU 0x40001000
TIM6_CR2	        EQU	0x40001004
TIM6_DIER	EQU	0x4000100C
TIM6_SR		EQU 0x40001010
TIM6_EGR	        EQU	0x40001014
TIM6_CNT	        EQU 0x40001024
TIM6_PSC	        EQU	0x40001028
TIM6_ARR	        EQU	0x4000102C
 
;CLOCK
RCC_APB2ENR	EQU	0x40021018	;Memory for configuring and enabling clock source
RCC_APB1ENR	EQU 0x4002101C
 
;Vector Table Mapped to Address 0 at Reset, Linker requires __Vectors to be exported
	AREA	RESET,DATA,READONLY
	EXPORT	__Vectors
 
__Vectors	
	DCD	INITIAL_MSP		;stack pointer at top of RAM
	DCD	Reset_Handler	;reset vector
	DCD	nmi_ISR			;interrupts
	DCD	h_fault_ISR
	DCD	m_fault_ISR
	DCD	b_fault_ISR
	DCD u_fault_ISR
 
	ALIGN
 
;My program, Linker requires Reset_Handler must be exported
	AREA	LCDDRAFT,CODE,READONLY
	EXPORT	Reset_Handler
	ENTRY
 
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Start up code
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Reset_Handler	PROC
 
clock_init
	;Enable TIM6 [4]
	ldr R6,=RCC_APB1ENR
	mov	R0,#0x0010 ;0000 0000 0001 0000
	str R0,[R6]
 
tim6_init
	;1 clock/ms = 1kHz
	;PSC = 8Mhz/1kHz - 1 = 7999  
	ldr R6,=TIM6_PSC
	mov R0,#7999
	str R0,[R6]
 
	ldr R6,=TIM6_ARR
	mov R0,#0xFFFF ;count all the way up
	str R0,[R6]
 
	ldr R6,=TIM6_CR1
	mov R0,#0x0005 ;[bit2]only under/overflow generates interrupt  [bit0]counter enable
	str R0,[R6]
 
	ldr R6,=TIM6_CNT
	mov R0,#0x0000 ;reset count to 0
	str R0,[R6]
 
;	mov R1,#0xFF
;delay
;	subs R1,#0x0001
;	cmp R1,#0x0000
;	bgt	delay
 
	ldr R6,=TIM6_SR
	mov R0,#0x0000
	str R0,[R6] ;clear the status register *BREAKPOINT HERE
 
	ENDP
 
;!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
; START OF MAIN PROGRAM 
;!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
main	PROC
 
	ldr R5,=TIM6_CNT ;get current count
	ldr R0,[R5]
 
	ldr R5,=TIM6_SR ;get status register
	ldr R1,[R5]
 
	b main
 
	ALIGN
	ENDP
 
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Interrupt Handlers
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
	AREA HANDLERS,CODE,READONLY
	;default handlers for interrupts and faults
	;all are infinite loop
nmi_ISR
	b	.
h_fault_ISR
	b	.
m_fault_ISR
	b	.
b_fault_ISR
	b	.
u_fault_ISR
	b	.
 
	END

Thanks in advance. ANY suggestions are appreciated at this point.