Having such a hard time with PROGMEM.......resets ESP....
Posted:
Mon Oct 26, 2015 9:02 pmby winneymj
Hi,
I am having such a hard time reading from PROGMEM. Below is a sample program that I though would work, but it causes the ESP to reboot/reset. Any ideas what I am doing wrong here. FYI this is being compiled and uploaded in the Arduino IDE.
Appreciated
Mark.
Code: Select all#include <pgmspace.h>
static const char PROGMEM Line1[] = {"String 1"};
static const char PROGMEM Line2[] = {"String 2"};
static const char PROGMEM Line3[] = {"String 3"};
const char * const Lines [] PROGMEM = { Line1, Line2, Line3 };
void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
delay(5000);
char buffer[20] = {0};
strcpy_P(buffer, (char*) pgm_read_word( &(Lines[0]) ) );
Serial.print("buffer=");
Serial.println(buffer);
}
void loop() {
// put your main code here, to run repeatedly:
}
Re: Having such a hard time with PROGMEM.......resets ESP...
Posted:
Tue Oct 27, 2015 1:22 amby eduperez
If "Lines" is defined as an array of "char *", then "Lines[0]" is a pointer to the first item in the array; thus, in the call to pgm_read_word, you do not need to add and extra "&". I would guess that you should do "pgm_read_word(Lines[0])" instead.
Hope my rusty C is not that rusty...
Re: Having such a hard time with PROGMEM.......resets ESP...
Posted:
Tue Oct 27, 2015 5:11 pmby winneymj
eduperez wrote:If "Lines" is defined as an array of "char *", then "Lines[0]" is a pointer to the first item in the array; thus, in the call to pgm_read_word, you do not need to add and extra "&". I would guess that you should do "pgm_read_word(Lines[0])" instead.
Hope my rusty C is not that rusty...
Hi,
I figured out the problem. It seems that pointers on the ESP8266 are 4 bytes (32 bits) and the call
pgm_read_word only returns a 16 bit number. It needs to be changed to
pgm_read_dword to get back a 32 bit pointer. New code sample is below.
Code: Select all#include <pgmspace.h>
static const char PROGMEM Line1[] = {"String 1"};
static const char PROGMEM Line2[] = {"String 2"};
static const char PROGMEM Line3[] = {"String 3"};
const char * const Lines [] PROGMEM = { Line1, Line2, Line3 };
void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
delay(5000);
char *ptrSize;
Serial.print("prtSize=");
Serial.println(sizeof(ptrSize));
char buffer[20] = {0};
strcpy_P(buffer, (char*) pgm_read_dword(&(Lines[0])));
Serial.print("buffer=");
Serial.println(buffer);
}
void loop() {
// put your main code here, to run repeatedly:
}