Diff: functions.s

Revision:

0:5446675502f2

diff -r 000000000000 -r 5446675502f2 functions.s
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/functions.s	Wed Apr 22 15:14:54 2020 +0000
@@ -0,0 +1,83 @@
+;   @file   main.S
+;   @author Gastón SALAZAR  <gaston_salazar@yahoo.com>
+;
+;   @brief  A blink program for the STM32F446re in assembly.
+;           It implements a state machine. It requires a basic
+;           C++ main function.
+;
+;   This example is used as a didactical resource.
+
+    AREA    functions_asm, CODE, READONLY
+
+;   Interface
+
+;   @def    LED
+;   @brief  The bit address of pin 5 on port A.
+LED     EQU (1 << 5)
+
+;    @def    DELAY
+;    @brief  The number of loops to execute before changing th state of LED.
+DELAY   EQU 5000000
+
+RCC_AHB1ENR EQU 0x40023830  ; Register for enabling the AHB1 clock for GPIOA
+GPIOAEN     EQU (1 << 0)
+
+GPIOA       EQU 0x40020000  ; Base address of port-A registers
+
+
+GPIO_MODER  EQU 0x00    ; Offsets of the registers for port X,
+GPIO_PUPDR  EQU 0x0c    ; using as base the port address
+GPIO_ODR    EQU 0x14
+
+RESET_MODER5    EQU (3 << 10)   ; Bit addresses in the port registers, in order to configure the behaviour of the output pin
+SET_MODER5      EQU (1 << 10)
+RESET_PUPDR5    EQU (3 << 10)
+
+    EXPORT setup
+
+setup   ; Machine setup
+
+    ; Enable port A
+    LDR R0, =RCC_AHB1ENR    ; R0 = RCC_AHB1ENR
+    LDR R1, [R0]            ; R1 = *R0
+    ORR R1, R1, #GPIOAEN     ; R1 = R1 | GPIOAEN
+    STR R1, [R0]            ; *R0 = R1
+
+    ; A minimal initialization for PA5 as output (LED) on the STM32F446re
+    LDR R3, =GPIOA
+
+    LDR R1, [R3, #GPIO_MODER]    ; R1 = R3[GPIO_MODER]
+    BIC R1, R1, #RESET_MODER5    ; R1 = R1 & ~RESET_MODER5
+    ORR R1, R1, #SET_MODER5
+    STR R1, [R3, #GPIO_MODER]    ; R3[GPIO_MODER] = R1
+
+    LDR R1, [R3, #GPIO_PUPDR]
+    BIC R1, R1, #RESET_PUPDR5
+    STR R1, [R3, #GPIO_PUPDR]
+
+;    State initilization
+    ; LED = 0
+    LDR R1, [R3, #GPIO_ODR]
+    BIC R1, R1,#LED
+    STR R1, [R3, #GPIO_ODR]
+
+    BX      LR
+    
+    ALIGN
+    EXPORT loop
+loop
+;    State update
+    LDR R3, =GPIOA
+    LDR R0, =DELAY
+loop1
+    CBNZ    R0, wait           ; if (R0!=0) goto wait
+    LDR     R1, [R3, #GPIO_ODR]
+    EOR     R1, R1, #LED        ; R1 = R1 ^ LED
+    STR     R1, [R3, #GPIO_ODR]
+    LDR     R0, =DELAY
+wait
+    SUB     R0, R0, #1           ; R0 = R0 - 1
+    B       loop1                ; goto loop
+
+    BX      LR  ; end of function main, to never be reached
+    END
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