Take input from button & generate output to LED in ASM

[jameshayek]

Hello all, thanks for the community, you guys are great, I was able to make progress from my last post.

I have a question in regard to my code for a project I started in school.

I was able to equate addresses, initialize the clock pins, and define the I/O pins for use.

I wrote a code that steps through the three colors on the on board LED. What I aim to do now, is to take input from a pin PORTA_PCR13 and set the led to one color when the button is not pressed, and another color when the button is pressed.

In C++ I would use an If, Then statement. However, I am unsure as to how I can implement this in ASM. Below is my code.

Any advice?

;Memory Address information found in the KL25P80M48SF0RM document ||||||||||||||||
;/////////////////////////////////////////////////////////////////////////////////
SIM_SCGC5   EQU  0x40048038     ;SIM_SCGC5 address            The control for each ports Clock Gate 
PORTB_PCR18 EQU  0x4004A000 + 4 * 18 ;PORTB_PCR18 address     LED Pin for RED
;Our added code to the example code found above in the lab manual
PORTB_PCR19 EQU  0x4004A04C     ;PORTB_PCR19 address          LED Pin for GREEN
PORTA_PCR13 EQU  0x40049034    ;PORTA_PCR13 address       Pin used for button
PORTD_PCR1  EQU  0x4004C004   ;PORTD_PCR1 address           LED Pin for BLUE
GPIOA_PDDR  EQU  0x400FF014     ;GPIOA_PDDR Register Address  PDDR is Port Data Direction Register  
GPIOB_PDDR  EQU  0x400FF054     ;GPIOA_PDDR Register Address  This sets the pin as input or output
GPIOD_PDDR  EQU  0x400FF0D4     ;GPIOB_PDDR Register Address
GPIOA_PDIR  EQU  0x400FF010  ;GPIOA_PDIR Register Address  This is the Port Data Input Register
 
GPIOB_PDOR EQU   0x400FF040
GPIOD_PDOR EQU   0x400FF0C0
 
 AREA asm_area, CODE, READONLY
 EXPORT  asm_main
asm_main  ;assembly entry point for C function, do not delete
; Add program code below here

;Initialize clock pins |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
;/////////////////////////////////////////////////////////////////////////////////
 BL  init_gpio 
loop 
 B loop
 
init_gpio
 LDR R0,=SIM_SCGC5     ;Load address of SIM_SCGC5 to R0
 LDR R1,[R0]           ;Put value of SIM_SCGC5 into R1
 LDR R2,=0x00003E00    ;Load value to turn on all port clocks into R2
 
 ORRS R1,R2            ;OR R2 into R1 for use of masking
 STR R1,[R0]           ;Put value back into SIM_SCGC5, 
;This puts 0011111000000000, bianary of 3E, into the Sim_SCGC5 register
;Which turns on the port clocks A-E. See Onur Yilmaz - GPIO.ppt Slide 3
 
 LDR R0,=PORTB_PCR18 ;Load address of PORTB_PCR18 to R0
 LDR R1,=0x00000100 ;Load value to R1
 STR R1,[R0]        ;Put value into PORTB_PCR18
 
 
 LDR R0,=PORTB_PCR19 ;Load address of PORTB_PCR19 to R0
 LDR R1,=0x00000100 ;Load value to R1
 STR R1,[R0]        ;Put value into PORTB_PCR19
 
 LDR R0,=PORTD_PCR1 ;Load address of PORTD_PCR1 to R0
 LDR R1,=0x00000100 ;Load value to R1
 STR R1,[R0]        ;Put value into PORTD_PCR1

 LDR R0,=PORTA_PCR13 ;Load address of PORTA_PCR13 to R0
 LDR R1,=0x00000102 ;Load value to R1
 STR R1,[R0]        ;Put value into PORTA_PCR13
 
;\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ 
;Initialize GPIO's and setup I/O status ||||||||||||||||||||||||||||||||||||||||||
;/////////////////////////////////////////////////////////////////////////////////
 LDR R0,=GPIOA_PDDR   ;Load address of GPIOA to R0
 LDR R1,=0x00000000   ;Load value to R1     Set to ALL INPUTS. O input, 1 Output. Convert to Binary to see what PTB is set
 STR R1,[R0]          ;Put value into GPIOA           
 
 LDR R0,=GPIOB_PDDR   ;Load address of GPIOB to R0
 LDR R1,=0x000C0000   ;Load value to R1      Outputs configured on PTB18 and PTB19, the LEDs on thos ports as outputs
 STR R1,[R0]          ;Put value into GPIOB
 
 LDR R0,=GPIOD_PDDR   ;Load address of GPIOD to R0
 LDR R1,=0x00000002   ;Load value to R1      Output configured on PTC1
 STR R1,[R0]          ;Put value into GPIOD
 
 
 ;this is where a loop would exist
 ;read the PDIR to take an input and branch to a location that will enable the color
;loop
 ;LDR R0,=GPIOA_PDIR
 ;LDR R1,[R0]
 ;LDR R2, =0x00002000         ;Must check this block of code    
 ;ANDS R1,R2     ;Not sure if it takes an input from pin A13
 ;CMP R1,R2
 ;BEQ loop
 
 LDR R0,=GPIOB_PDOR
 LDR R1,=0xFFFFFFFF
 STR R1,[R0]
 
 LDR R0,=GPIOD_PDOR
 LDR R1,=0xFFFFFFFF
 STR R1,[R0]
  
 LDR R0,=GPIOB_PDOR
 LDR R1,=0x00040000
 STR R1,[R0]
 
 LDR R0,=GPIOB_PDOR
 LDR R1,=0xFFFFFFFF
 STR R1,[R0]
 
 LDR R0,=GPIOB_PDOR
 LDR R1,=0x00080000
 STR R1,[R0]
 LDR R0,=GPIOB_PDOR
 LDR R1,=0xFFFFFFFF
 STR R1,[R0]
 
 LDR R0,=GPIOD_PDOR
 LDR R1,=0xFFFFFFFD
 STR R1,[R0] 
 
 LDR R0,=GPIOD_PDOR
 LDR R1,=0xFFFFFFFF
 STR R1,[R0] 
 
 BX LR
 
;Control indivual pins or LED's ||||||||||||||||||||||||||||||||||||||||||||||||||
;/////////////////////////////////////////////////////////////////////////////////
 
 LDR R2, =0x00000000  ;Counter to see Iif button is held down
 LDR R4,= 0x00000000  ;Counter for LED COLOR CYLE
 
 
 
 
 
 
 
 
;///////////////////////////////////////////////////
; Put constants here
 
 AREA data_area, DATA, READWRITE
; Put variables here
 
 END

Thanks in advance.

[mjbcswitzerland]

James

Read the value to a register, mask the bit of interest and then do a compare.

CMP R0, #0

BEQ.N _label1

do things when true and return or jump to _label2

_label1

do things when false

_label2

continue

However you really should start using C asap because I don't think anyone is really interested with messing about in assembler (maybe back in the 1970s it would have been used). In any case just write what you want in C and see what the compiler spits out in assembled code since it is the easiest way to learn.

Regards

Mark

[jameshayek]

After reviewing your first comment and code I wrote the following (this was placed after my block of comments and before clearing GPIOB_PDOR):

	LDR R0,=GPIOA_PDIR
	LDR R1,[R0]
	LDR R2, =0x00002000         ;Mask the bit of interest, this is for PTA13
	ANDS R1,R2
	CMP R1,R2                         ;Compare the results
	BEQ _onColor

_offColor

	LDR R0,=GPIOB_PDOR
	LDR R1,=0x00080000
	STR R1,[R0]

_onColor

	LDR R0,=GPIOD_PDOR
	LDR R1,=0xFFFFFFFD
	STR R1,[R0]

I shorted pin PTA13 to ground and when I step through the code, I expected to see the pin color I specified light up, yet it does not. This code chronologically steps throgh each line, dispite creating the labels _onColor and _offColor

.

I am not sure what I am doing wrong.

I did not know I could write in C then transcribe to ASM. I will try that for the next assignment, this ASM is 90% done. All I need is to get the button functionality for this project.

The class is 50% ASM and 50% C

[yasuhikokoumoto]

Hello james,

I wrote a part of the code according to Mr. Mark's instructions.

It was a little modified to pass the GCC assembler.

LOOP:
 LDR R0,=GPIOA_PDIR
 LDR R1,[R0]  
 LDR R2, =0x00002000
 AND R1,R2      
 BNE _onColor




_offColor:
LDR R0,=GPIOB_PDOR 
 LDR R1,=0x00080000 
 STR R1,[R0]
 B  NEXT

_onColor:
 LDR R0,=GPIOD_PDO LDR R1,=0xFFFFFFFD  STR R1,[R0]

NEXT:
/* do something?  */
B  LOOP

Can it help you?

Best regards,

Yasuhiko Koumoto.

[jameshayek]

Thank you for everyone's help.

I was able to take information learned from Mark as well as a buddies sample code, and write this code which works like expected.

loop
  LDR R0,=GPIOA_PDIR
  LDR R1,[R0]
  LDR R2, =0x00002000         ;Mask the bit of interest    
  ANDS R1,R2
  LDR R6, =0x00000000;
  CMP R1, R6                  ;Test to see if button is pressed
  BNE _offColor


_onColor
  LDR R0,=GPIOD_PDOR
  LDR R1,=0xFFFFFFFF     ;Clears the registers
  STR R1,[R0]
  LDR R0,=GPIOB_PDOR
  LDR R1,=0xFFFFFFFF     ;Also clears the registers
  STR R1,[R0]
  LDR R1,=0x00080000
  STR R1,[R0]
  LDR R0,=GPIOD_PDOR
  LDR R1,=0xFFFFFFFD
  STR R1,[R0]
  B loop

_offColor
  LDR R0,=GPIOB_PDOR
  LDR R1,=0xFFFFFFFF     ;This clears the register
  STR R1,[R0]
  LDR R0,=GPIOD_PDOR
  LDR R1,=0xFFFFFFFF     ;This also clears the registers for the other color pin
  STR R1,[R0]
  LDR R0,=GPIOB_PDOR
  LDR R1,=0x00080000     ;This sets the color of the pin of choice.
  STR R1,[R0]
  B loop

yasuhikokoumoto, your code looks much more simpler then mine. I am going to try to rewrite it using your code and see if I can get it to work as well.

Thank you mjbcswitzerland

[mjbcswitzerland · Accepted solution]

James

You will need to check the register contents and also the CCR flags that are affected when stepping.

- the CMP is not required because the AND already sets the CCR with the result of whether it was zero or not

- you certainly need a jump after the first block otherwise it just continues into the second and you always have the same result at the end

Regards

Mark