discussion05

Dicussion 05

Ryan Robucci

Objectives

Storage
LCD
Debugging mdb/gdb

References

MPLAB® XC8 C Compiler User’s Guide for AVR® MCU
https://ww1.microchip.com/downloads/en/DeviceDoc/MPLAB XC8 C Compiler UG for AVR MCU 50002750C.pdf

SCL User Guide:
file:///opt/microchip/mplabx/v5.50/mplab_platform/mplab_ide/modules/docs/SCL_Users_Guide/index.html

Memory Space

Usage as reported by debugger:

Report using size command:

robucci@sensi:~/MPLABXProjects/discussion05.X/dist/default/production$ /opt/microchip/xc8/v2.32/avr/bin/avr-size discussion05.X.production.elf

   text	   data	    bss	    dec	    hex	filename
    460	    108	      0	    568	    238	discussion05.X.production.elf

.text is the program code size, an in this case includes blocks representing variables that will be stored in the program, flash memory
.data is the part of the object file that will be used to initialize statically-allocated variables, and corresponds to a variables that will be statically allocated in RAM during execution
.bss is global, typically initialized to zero
The last two columns, dec and hex sums totals, reported in decimal and hexadecimal

Next I add a compile option to disable the default behavior in this tool of placing static constants in program memory:

-mno-const-data-in-progmem

And this is the new result:

   text	   data	    bss	    dec	    hex	filename
    438	    112	      0	    550	    226	discussion05.X.debug.elf

What happened?

IN THIS SYSTEM, THE DEFAULT IS THAT constants are stored and accessed from program memory.

In older versions of the compiler, macros and directive were required to place constants, including constant literal strings in program memory:

https://www.csee.umbc.edu/~alnel1/cmpe311/discussions/Discussion6.pdf

https://www.arduino.cc/reference/en/language/variables/utilities/progmem/

Find the -mno-const-data-in-progmem option in the compiler user manual:

MPLAB® XC8 C Compiler User’s Guide for AVR® MCU
https://ww1.microchip.com/downloads/en/DeviceDoc/MPLAB XC8 C Compiler UG for AVR MCU 50002750C.pdf

LCD

Connection of LCD Array

AVR Butterfly Evaluation Kit:
http://ww1.microchip.com/downloads/en/devicedoc/doc4271.pdf Section 3.4 LCD Display

AVR065: LCD Driver for the STK502

https://www.microchip.com/content/dam/mchp/documents/OTH/ApplicationNotes/ApplicationNotes/doc2530.pdf

Array of segments available on LCD Glass Pannel on AVR (similar to STK502 devkit)

Provided Driver Files:

📄 discussion05.c

📄 U0_LCD_Driver.c

📄 U0_LCD_Driver.h

Goto file U0_LCD_Driver.c and note this line:

0x2A80,     // '+'

How does 0x2A80 correspond to +, according to the bit mapping?

Updating Debug Clock Freq.

Seems to help with debugging while using stdio

mdb

//file:simple.c
//author: Robucci

#include <avr/io.h>

void bubble4(volatile int arr[]){
  int i;
  int tmp;
  for (i=0;i<3;i++){
    if (arr[i+1]>arr[i]){
      if (PINB){
        tmp=arr[i];
        arr[i]=arr[i+1];
        arr[i+1]=tmp;
      }
    }
  }  
}

int main(){
  DDRB=0x0F;
  int arr[]={0xFF,10,30,40};
  arr[0]=50;
  int i;
  while(1){
    for (i=0;i<3;i++){
      arr[i++]=PINA;
      bubble4(arr);
      PORTB=arr[i++];
    }    
  };
}

#mdb.cmd

device atmega169p

# for hw
set AutoSelectMemRanges auto
set communication.speed 1.00
set memories.programmemory true

#for sim
set oscillator.frequencyunit None
set oscillator.frequency 8000000
set breakoptions.stimulusmessages.notes Report
set codecoverage.enabled Disable

#hwtool sim

set communication.interface jtag
hwtool snap

program ./a.out
# may need the following for sim
# upload
rest
#reset MCLR
Sleep 1500
#watch PORTB W
#stim stim.scl
#b main
#run

Compile program

/opt/microchip/xc8/v2.32/bin/xc8-cc -mcpu=atmega169p -Wall -O0 -g simple.c

Start gdb

sudo /opt/microchip/mplabx/v5.50/mplab_platform/bin/mdb.sh mdb.cmd

Commands to run:

b simple.c:23
reset
run
bt full
print arr
print /a arr
b bubble4
run
list
stepi
list
bt full
x 256

example command

>bt full                                                                                                                                               ?
#0  main () at /home/robucci/GIT/cmpe311/mdb/first_c/simple.c:13
    arr =

Note: if running on the simulator, this command is useful

stopwatch

print arr seems to fail. it seems that a mapping or linker file might be needed, but the memory can be seen with x

Get the address of arr

>print /a arr                                                                                                                  ?

Address range starting at 256

>x /h256  256                                                                                                                  ?
00ff   000a   001e   0028   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   
0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000   0000

gdb

(if time allows)

Old Discussion for Moving Variables to Program Space

Tips for using program space

What happens when you run out of memory ?
Data should be below 1K bytes
Shorten your prompts (reuse parts of your string)
Don't have multiple temporary string variables in memory at the same time
Have gcc optimize for space
(include -Os option during compilation )
Check your stack pointer
printf("sp:%d\n",SP);
Documentation for memory sections available from he

Using program space

AVR has a library for keeping const data in program memory (flash) and accessing it directly instead of using RAM

Program Memory has 16KB space
Example functions available in stdio.h
printf_P
sprintf_P
fprintf_P
fputs_P
fscanf_P

#include <avr/pgmspace.h>

Declare const strings using special flag PROGMEM

//PROGMEM used to locate a variable in flash ROM
const PROGMEM char myString[] = "Repeated Use";

you can create special pointers using PGM_P and access the data using a
special macro pgm_read_byte

Documentation is available online

PGM_P progPtr;
progPtr =myString;
//Somewhere in your code
while(pgm_read_byte(progPtr)!=’\0’){
printf("%c",pgm_read_byte(progPtr));
progPtr++;
}

#include <avr/pgmspace.h>
void lcd_puts_P(const char c[]) { //same const char *c
uint8_t ch = pgm_read_byte(c);
while(ch != 0) {
lcd_putc(ch);
ch = pgm_read_byte(++c);
} }
// Usage: Note PSTR macro which simplifies placing string
// literals in flash ROM
// Code: lcd_puts_P(PSTR("Hello World"));
// Or: const PROGMEM char SOME_STRING[] = "Repeated Use";
// lcd_puts_P(SOME_STRING)