stm32l100-asm-bootstrap/main.asm

;***************************************************************************************************
;*
;* Misto            : CVUT FEL, Katedra Mereni
;* Prednasejici     : Doc. Ing. Jan Fischer,CSc.
;* Predmet          : A4M38AVS, A4B38NVS
;* Vyvojovy Kit     : STM32L100 DISCOVERY (STM32L100RC)
;* Datum            : 12/2010, 10/2015
;* Autor            : Michal TOMAS (2010), Ondrej Hruska (2015)
;*
;***************************************************************************************************

;***************************************************************************************************
;* Include library files
;***************************************************************************************************

		; Register addresses
		GET		lib/INI_REGS.s

		; Bit presets
		GET		lib/INI_BITS_GPIO.s
		GET		lib/INI_BITS_RCC.s
		GET		lib/INI_BITS_FLASH.s
		GET		lib/INI_BITS_SYSTICK.s
		GET		lib/INI_BB.s


;***************************************************************************************************
;* Start program AREA and pass compiler flags to the startup script...
;***************************************************************************************************

		AREA    MAIN, CODE, READONLY

		; This is a compiler flag imported by the startup script.
__use_two_region_memory
		EXPORT __use_two_region_memory


;***************************************************************************************************
;* System config (clock, ports, timers...)
;*
;* Called by the startup script before calling __main
;***************************************************************************************************

SystemInit
		EXPORT	SystemInit				; Export the address to startup script
				PUSH	{LR}
				BL		RCC_CNF			; Configure clock sources
				BL		GPIO_CNF		; Configure GPIO power and pin settings
				BL		SYSTICK_CNF		; Configure SysTick timer
				POP		{PC}



;***************************************************************************************************
;* Interrupt handlers...
;***************************************************************************************************

SysTick_Handler
		EXPORT SysTick_Handler			; Export the address to startup script (replaces a WEAK stub)
				PUSH {LR}

				; Toggle the PC8 LED (bit-banding access)
				LDR		R0, =BB_GPIOC_ODR_9
				LDR		R1, [R0]
				EOR		R1, R1, #1
				STR		R1, [R0]

				; alternative - writing the register
;				LDR		R0, =GPIOC_ODR
;				LDR		R1, [R0]
;				EOR		R1, R1, #GPIO9
;				STR		R1, [R0]

				POP {PC}



;***************************************************************************************************
;* Main function
;*
;* Called by the startup script after SystemInit.
;* __main is called only once, and does not return!
;***************************************************************************************************

__main
		EXPORT	__main				; Export the address to startup script
				ENTRY				; Marks the program entry point (shouldnt be here)
LOOP
				; blink the other led slowly

				; (using bit-banding)
				LDR		R0, =BB_GPIOC_ODR_8
				LDR		R1, [R0]
				EOR		R1, R1, #1
				STR		R1, [R0]

				; (writing the entire register) - can cause race condition with SysTick interrupt
;				LDR		R0, =GPIOC_ODR
;				LDR		R1, [R0]
;				EOR		R1, R1, #GPIO8
;				STR		R1, [R0]

				MOV		R0, #50
				BL		DELAY

				B LOOP



;**************************************************************************************************
;* GPIO configuration
;*
;* Sets PC08 and PC09 as outputs, PA0 as input.
;**************************************************************************************************

GPIO_CNF
				PUSH	{R0,R1,LR}

				; Enable GPIO peripheral timing
				LDR		R0, =RCC_AHBENR ; Advanced High-speed Bus ENable Register
				LDR		R1, [R0]
				LDR		R2, =(RCC_AHBENR_GPIOAEN :OR: RCC_AHBENR_GPIOCEN)
				ORR		R1, R1, R2
				STR		R1, [R0]

				; Output pins C8, C9
				LDR		R0, =GPIOC_MODER
				LDR		R1, [R0]
				BIC		R1,R1, #(GPIO_MODER_8 :OR: GPIO_MODER_9)
				ORR		R1,R1, #(GPIO_MODER_8 :OR: GPIO_MODER_9) & GPIO_MODER_OUTPUT
				STR		R1, [R0]

				; Input pin A0
				LDR		R0, =GPIOA_MODER
				LDR		R1, [R0]
				BIC		R1,R1, #GPIO_MODER_0                      ; Clear the bit config area
				ORR		R1,R1, #(GPIO_MODER_0 & GPIO_MODER_INPUT) ; Write the "input" pattern into the bit config area
				STR		R1, [R0]

				POP		{R0,R1,PC}



;**************************************************************************************************
;* SysTick configuration
;*
;* Configures SysTick to fire a SysTick interrupt at 1 Hz
;**************************************************************************************************

SYSTICK_CNF
				PUSH	{R0, R1, LR}

				; Use the core clock (undivided)

				LDR		R0, =SysTick_CSR
				LDR		R1, [R0]
				ORR		R1, R1, #SysTick_CSR_CLKSOURCE_CORE
				STR		R1, [R0]

				; Configure the reload register to 1s

				LDR		R1, =0xFFFFFF
				LDR		R0, =SysTick_RELOAD
				STR		R1, [R0]

				; Enable SysTick interrupt & start counting

				LDR		R0, =SysTick_CSR
				LDR		R1, [R0]
				ORR		R1, R1, #(SysTick_CSR_TICKINT :OR: SysTick_CSR_ENABLE)
				STR		R1, [R0]

				POP		{R0, R1, PC}



;**************************************************************************************************
;* Delay routine
;*
;* Inputs:	R0 = number of loop cycles
;**************************************************************************************************

DELAY
				PUSH	{R2, LR}		; Push the changed registers & link register

WAIT_OUTER		; Outer loop
				LDR		R2, =40000		; Length of inner loop

				; Inner loop
WAIT_INNER		SUBS	R2, R2, #1		; Decrement INNER loop counter
				BNE		WAIT_INNER		; Continue the loop if not done

				SUBS	R0, R0, #1		; Decrement OUTER loop counter
				BNE		WAIT_OUTER		; Continue the loop if not done

				POP		{R2, PC}		; Pop & return



;***************************************************************************************************
;* Konfigurace systemovych hodin a hodin periferii
;*
;* Nastavi hodiny na HSI 16 MHz
;**************************************************************************************************

RCC_CNF
				PUSH	{R0, R1, LR}

				; Flash timing configuration
				LDR		R0, =FLASH_ACR
				LDR		R1, [R0]
				ORR		R1, R1, #FLASH_ACR_ACC64
				STR		R1, [R0]

				LDR		R1, [R0]
				ORR		R1, R1, #(FLASH_ACR_PRFTEN :OR: FLASH_ACR_LATENCY)
				STR		R1, [R0]

				; Nastavit hodinove vstupy
				LDR		R0, =RCC_CR

				; Additional RCC_CR config
;				LDR		R1, [R0]
;				LDR		R2, =RCC_CR_RTCPRE ; clear RTC prescaler
;				BIC		R1, R1, R2
;				; HseByp allows to use external clock source with HSEON
;				LDR		R2, =(RCC_CR_RTCPRE_DIV2 :OR: RCC_CR_HSEBYP)
;				ORR		R1, R1, R2
;				STR		R1, [R0]

				; Power on HSI (runs from MSI on start)

				LDR		R1, [R0]
				ORR		R1, R1, #RCC_CR_HSION
				STR		R1, [R0]

				; Wait for HSIRDY
				ALIGN
NO_HSI_RDY		LDR		R1, [R0]
				TST	 	R1, #RCC_CR_HSIRDY
				BEQ 	NO_HSI_RDY

				; Select HSI as the core clock source

				LDR		R0, =RCC_CFGR
				LDR		R1, [R0]
				BIC		R1, R1, #RCC_CFGR_SW
				ORR		R1, R1, #RCC_CFGR_SW_HSI
				STR		R1, [R0]

				POP		{R0, R1, PC}


;**************************************************************************************************

				ALIGN	; Adds NOP if needed to complete a 32-bit word
				END