Can't enable PLL properly for STM32F767

[Helder Sales]

Hi,

I'm having a hard time configuring the system clock. It seems that I'm achieving 16MHz, but I want to run at full speed (216MHz). From what I'm seeing, the problem is that the System Clock Switch isn't changing to PLL. If I try to change bits 1:0 in the RCC_CFGR register, the status returns that the HSI is enabled.

RCC_BASE		EQU		0x40023800
RCC_CR			EQU		RCC_BASE				;offset 0x00
RCC_CFGR		EQU		0x40023808				;offset 0x08
RCC_PLLCFGR		EQU		0x40023804				;offset 0x04
RCC_AHB1ENR		EQU		0x40023830  			;offset 0x30
	
GPIOB_BASE		EQU		0x40020400	
GPIOB_MODER		EQU		GPIOB_BASE				;offset 0x00
GPIOB_ODR		EQU		0x40020414				;offset 0x14
	
GPIOB_EN		EQU		(1 << 1)
MODER0_OUT		EQU		(1 << 0)
	
PLLM			EQU		(4 << 0)
PLLN			EQU		(216 << 6)
PLLP			EQU		((0 << 16) :OR: (0 << 17))
PLLQ			EQU		(9 << 24)
PLLHSE			EQU		(1 << 22)
 
				AREA	STM32, CODE, READONLY
				ENTRY
				EXPORT	__main
			
__main
				BL		ENABLE_CLOCK
				BL		ENABLE_GPIOB
				B		CONTINUE
		
ENABLE_CLOCK
				LDR		R0, =RCC_CR
				LDR		R1, [R0]			
				ORR		R1, #(1 << 18)	;HSE BYPASS
				STR		R1, [R0]
				LDR		R0, =RCC_CR
				ORR		R1, #(1 << 16)	;HSE ENABLE
				STR		R1, [R0]
			
HSE_READY		LDR		R0, =RCC_CR	;LOOP UNTIL READY
				LDR		R1, [R0]
				AND		R1, #(1 << 17)
				MOVS	R0, R1
				BEQ		HSE_READY						
				
				LDR		R0,	=RCC_PLLCFGR  ;SET 216MHZ CLOCK
				LDR		R1, [R0]
				ORR		R1, #PLLM
				ORR		R1, #PLLN
				ORR		R1, #PLLP
				ORR		R1, #PLLQ
				ORR		R1, #PLLHSE
				STR		R1, [R0]	
				
				LDR		R0, =RCC_CR
				LDR		R1, [R0]
				ORR		R1, #(1 << 24)  ;PLL ON
				STR		R1, [R0]
		
PLL_LOCK		LDR		R0, =RCC_CR	;LOOP UNTIL READY
				LDR		R1, [R0]
				AND		R1, #(1 << 25)
				MOVS	R0, R1
				BEQ		PLL_LOCK
				
				LDR		R0,	=RCC_CFGR
				LDR		R1, [R0]
				ORR		R1, #(2 << 0)  ;PLL AS SYSCLK
				STR		R0,	[R0]
			
;SYSCLK_STATUS	LDR		R0, =RCC_CFGR  ;LOOP UNTIL READY
;				LDR		R1, [R0]
;				AND		R1, #(2 << 2)
;				MOVS	R0, R1
;				BEQ		SYSCLK_STATUS
				
				BX		LR
		
ENABLE_GPIOB
				LDR		R0,	=RCC_AHB1ENR  ;EN GPIO CLOCK
				LDR		R1, [R0]
				ORR		R1,	#GPIOB_EN
				STR		R1, [R0]
				
				LDR		R0, =GPIOB_MODER  ;SET OUTPUT
				LDR		R1, [R0]
				ORR 	R1, #MODER0_OUT
				STR		R1, [R0]
				
				BX		LR
 
CONTINUE
				LDR		R1,	=GPIOB_ODR  ;OUTPUT DATA REGISTER
				MOVW	R0, #(1 << 0)
		
BLINK
				LDR		R2, =16000000
				EOR		R0, #(1 << 0)
				STR		R0, [R1]
				
				BL		DELAY
				
				B		BLINK
 
DELAY
				SUBS	R2,	R2,#1
				
				BNE		DELAY
				
				BX		LR
 
				ALIGN
				END

I'm doing the following steps: set HSE to bypass, enable HSE, set PLLM, N, P and Q, enable PLL and finally (but not working) switching the system clock to PLL.

[Tesla DeLorean]

Line 67 needs to be STR R1,[R0]

[Helder Sales]

Oops, sorry about that. Finally got to pass the SWS verification. Thanks for the reply.

Also, corrected some mistakes regarding RCC_PLLCFGR configuration, like this

PLLMRST			EQU		~(0x1F << 0)
PLLM			EQU		(4 << 0)
PLLNRST			EQU		~(0xFF << 6)
PLLN			EQU		(216 << 6)
PLLP			EQU		~((0 << 16) :OR: (0 << 17))
PLLQ			EQU		(9 << 24)
PLLQRST			EQU		~(7 << 24)
PLLHSE			EQU		(1 << 22)
 
LDR	R0,=RCC_PLLCFGR		;SET 216MHZ CLOCK
LDR	R1, [R0]
AND	R1, #PLLMRST
ORR	R1, #PLLM
AND	R1, #PLLNRST
ORR	R1, #PLLN
AND	R1, #PLLP
AND	R1, #PLLQRST
ORR	R1, #PLLQ				
ORR	R1, #PLLHSE
STR	R1, [R0]	

And now, instead of blinking the LED at 1sec rate (adjusting the delay), the processor ignores everything (like, skips all the code) and suddenly goes to SystemInit() when reaching the end of code

And does nothing more after this. Never saw anything like that, maybe I misconfigured something?

[waclawek.jan]

Now this is strange: you write assembler yet don't single-step in disassember window?

JW

[Tesla DeLorean]

That's not very efficient. The Assembler is not going to fold that, you need to condense it manually. You should be able to perform a single masking AND, followed by a single OR.

You understand __main != main right?

The Reset_Handler code typically calls SystemInit() prior to calling __main, which in normal implementation initializes the statics and then calls to main()

Perhaps uniquely name your routine, and call THAT from the Reset_Handler, and not the other components.

[Helder Sales]

I renamed the main in the Reset_Handler. Now there shouldn't be any problem.

But, there's something wrong with the PLL switch, after the instruction to change the system clock, almost everything in the disassemble view turn MOVS r0,r0 and bugs.

I tried to reduce the clock below 216MHz, used 20 NOPs after changing the prescalers, but still nothing. The only way it worked was to divide the AHB by 8, but resulted in a clock less than 16MHz (from the blinking rate).

[Helder Sales]

Sorry, I'm just new to these kind of things. I'm still learning what's important and the assembly itself. Didn't used the disassembler window before, but thanks for pointing that out.

[Tesla DeLorean · Accepted solution]

The flash needs to be configured to the number of wait-states the new clock will need.

[Helder Sales]

That was the solution! Thank you very much!

I guess a lot of things have to be considered when you move from C using vendor APIs...

I'll study carefully how my device works to anticipate this kind of situation.