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Message |
x!nDy
Guest
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| reading flash memory one byte at a time. |
 Posted: Tue Jul 29, 2008 8:47 pm |
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Hi everyone, i am saving data in flash memory and these data are variable in length and are separated by a delimiter (*). So what i want to do is try to read flash one bit at a time and look for the (*). If i found an * then i would print the word. But i cant seem to get it to work. Here is my code.
| Code: |
FlashLoopRead=FlashStartAddress; //FlashLoopRead receives the last address in flash holding a certain value.
FlashStartAddress = FlashReadAddress; // FlashStartAddress receives the first address in flash holding a certain value
disable_interrupts(GLOBAL);
ii=0;
do
{
read_program_memory(FlashStartAddress, temp1, 1); // temp1 is char
msg[ii] = temp1; // msg[ii] is an array with a length of 80
if (msg[ii]=='*')
{
*(msg[ii])='\0';
FlashStartAddress = FlashStartAddress + ii;
fprintf(PC,"\n%s\n",msg);
ii=0;
justOnce=True; // justOnce is a boolean
}
if (!justOnce)
ii++;
justOnce=false;
}while(FlashStartAddress<=FlashLoopRead);
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So, if the contents of my flash memory is HELLO*WORLD!*, it would print HELLO
WORLD!
please help.. thanks in advance.. |
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Indy31
Guest
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| Posted: Wed Jul 30, 2008 3:37 am |
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Bug 1: read_program_memory() should be passed an address for storing the data read from flash. change: | Code: | | read_program_memory(FlashStartAddress, temp1, 1); // temp1 is char |
to: | Code: | | read_program_memory(FlashStartAddress, &temp1, 1); // temp1 is char |
Bug 2:
should have been:
| Code: | *(&msg[ii])='\0';
or
msg[ii]='\0'; |
General note 1: indirect addressing on the PIC is very inefficient and requires a lot of instructions. You can save memory and increase performance by minimizing array accesses. instead of: it is more efficient to write:
General note 2: Using 'justOnce' variables make your code difficult to understand. Instead of an if-if combination your code is faster and easier to understand if you use an if-else construction.
Regarding all above, here is my suggested code: | Code: | ii=0;
do
{
read_program_memory(FlashStartAddress, &temp1, 1); // temp1 is char
if (temp1=='*')
{
msg[ii]='\0';
FlashStartAddress = FlashStartAddress + ii;
fprintf(PC,"\n%s\n",msg);
ii=0;
}
else
{
msg[ii] = temp1; // msg[ii] is an array with a length of 80
ii++;
}
}while(FlashStartAddress<=FlashLoopRead); |
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x!nDy
Guest
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| Posted: Wed Jul 30, 2008 9:09 pm |
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hi.. thanks for the reply and explanation.. i really appreciate it.. however, when i try to use your code and try to look at the value of temp1, all it prints is 0.. can you tell me how this happened? here is my code:
| Code: |
ii=0;
do
{
read_program_memory(FlashStartAddress, &temp1, 1); // temp1 is char
fprintf(PC,"temp1 = %c\n",temp1); // prints value of temp1
if (temp1=='*')
{
msg[ii]='\0';
FlashStartAddress = FlashStartAddress + ii;
fprintf(PC,"\n%s\n",msg);
ii=0;
}
else
{
msg[ii] = temp1; // msg[ii] is an array with a length of 80
ii++;
}
}while(FlashStartAddress<=FlashLoopRead);
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RLScott
Joined: 10 Jul 2007
Posts: 465
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| Posted: Thu Jul 31, 2008 10:08 am |
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| x!nDy wrote: | hi.. thanks for the reply and explanation.. i really appreciate it.. however, when i try to use your code and try to look at the value of temp1, all it prints is 0.. can you tell me how this happened? here is my code:
| Code: |
ii=0;
do
{
read_program_memory(FlashStartAddress, &temp1, 1); // temp1 is char
fprintf(PC,"temp1 = %c\n",temp1); // prints value of temp1
if (temp1=='*')
{
msg[ii]='\0';
FlashStartAddress = FlashStartAddress + ii;
fprintf(PC,"\n%s\n",msg);
ii=0;
}
else
{
msg[ii] = temp1; // msg[ii] is an array with a length of 80
ii++;
}
}while(FlashStartAddress<=FlashLoopRead);
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You are not advancing FlashStartAddress when each character is read, so it seems that read_program_memory() will just read the same first byte over and over, and you will never get to the '*'. The msg[ii] = temp1 will eventually overflow the bounds of the msg[80] and trash some other memory and the program will crash. This will happen even if you did everything else right if the '*' is somehow absent. What did you see as a result of printout of temp1?
_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting |
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x!ndy
Guest
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| Posted: Thu Jul 31, 2008 8:23 pm |
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you are right.. it was really stupid of me..  it works fine now.. thanks.. |
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