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Inconsistent FRAM Read Results

 
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jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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Inconsistent FRAM Read Results
PostPosted: Wed Apr 04, 2007 2:07 pm     Reply with quote
18F6627 40MHz
FM25256 SPI FRAM
3.236

Hello All,

Battling a new one over the last few hours. If use sequential reads and writes everything works ok (or so it appears.) If I use individual reads and writes I get errors after writing more than 64 values in a FOR loop. And it appears that mixing a sequential write with a individual read causes problems.

Here is some code:

Code:

#define FRAM_SIZE    32768

void init_fram(void)
{
   delay_ms(15);  //FRAM is not available until 10ms after power-up
   setup_spi(SPI_MASTER | SPI_MODE_0_0 | SPI_CLK_DIV_4);
}

void write_int16_fram(int16 address, int16 value)
{
   output_low(FRAM_CS);       //select FRAM
   spi_write(WREN);           //enable writes, required prior to WRITE cmd
   output_high(FRAM_CS);      //de-select FRAM, required between each op-code
   delay_cycles(1);           //ensure compiler doesn't remove the pin toggle
   output_low(FRAM_CS);       //re-select the FRAM
   spi_write(WRITE);          // send the WRITE op-code
   spi_write(address);        //send the low byte of the address
   spi_write(address >> 8);   //send the high byte of the address
   spi_write(value);
   spi_write(value >> 8);
   output_high(FRAM_CS);      //de-select FRAM
}

int16 read_int16_fram(int16 address)
{
   int8  value_low;
   int8  value_hi;
   int16 value;
   output_low(FRAM_CS);      //re-select the FRAM
   spi_write(READ);          // send the WRITE op-code
   spi_write(address);       //send the low byte of the address
   spi_write(address >> 8);  //send the high byte of the address
   value_low = spi_read(0);
   value_hi  = spi_read(0);
   output_high(FRAM_CS);     //de-select FRAM
   value = make16(value_hi, value_low);
   return(value);
}

void write_int16_seq_fram(int16 start_addr, int16 *pntr, int16 count)
{
   if(start_addr + (count * 2) <= FRAM_SIZE)
   {
      //setup_spi(SPI_MASTER | SPI_MODE_0_0 | SPI_CLK_DIV_4);
      output_low(FRAM_CS);       //select FRAM
      spi_write(WREN);           //enable writes, required prior to WRITE cmd
      output_high(FRAM_CS);      //de-select FRAM, required between each op-code
      delay_cycles(1);           //ensure compiler doesn't remove the pin toggle
      output_low(FRAM_CS);       //re-select the FRAM
      spi_write(WRITE);          // send the WRITE op-code
      spi_write(start_addr);     //send the low byte of the address
      spi_write(start_addr>>8);  //send the high byte of the address
      do
      {
         //restart_wdt();        //uncomment if slow speeds
         spi_write(*pntr++);
         spi_write(*pntr++);
      } while(--count);
      output_high(FRAM_CS);      //de-select FRAM
   }
}

void read_int16_seq_fram(int16 start_addr, int16 *pntr, int16 count)
{
   if(start_addr + (count * 2) <FRAM_SIZE>>8);  //send the high byte of the address
      do
      {
         //restart_wdt();        //uncomment if slow speeds
         *pntr++ = spi_read(0);
         *pntr++ = spi_read(0);
      } while(--count);
      output_high(FRAM_CS);      //de-select FRAM
   }
}



I'm to a point where I'm not getting any sort of results that point me in a direction to look.

Any help would be appreciated,

John

EDIT:

I'm starting to think it may be a difference in the addressing between sequential and individual reads/writes?

Last edited by jecottrell on Wed Apr 04, 2007 5:28 pm; edited 1 time in total
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed Apr 04, 2007 2:16 pm     Reply with quote
Quote:
void write_int16_seq_fram(int16 start_addr, int16 *pntr, int16 count)

spi_write(*pntr++);
spi_write(*pntr++);

Your pointer is pointing to a 16-bit object. When you increment it,
it will increment by 2 bytes each time. Suppose pntr is initially set to 0.
After your first spi_write() statement, it will now point to address 2.

The same problem exists in the read routine.
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Wed Apr 04, 2007 2:22 pm     Reply with quote
THANK-YOU!

I'll read up on it and try to clean it up this evening and test it out.

John
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Wed Apr 04, 2007 5:38 pm     Reply with quote
OK. I'm going to ask for some spoon feeding.... (or a good tutorial on pointers). I only brought one C book into the office this evening and it doesn't cover this stuff in very good detail. (O'Reilly Practical C)

I can think of a couple of ways to kludge something together, but I'm sure they're probably not the recommended ways... or probably won't work for some subtle reason.

Code:
void write_int16_seq_fram(int16 start_addr, int8 *pntr, int16 count)


or maybe...

Code:
void write_int16_seq_fram(int16 start_addr, int16 *pntr, int16 count)

spi_write(*pntr++);
spi_write(*(pntr-1));



Thanks,

John

EDIT:

After a quick bit of reading and even smaller bit of thinking... it looks like the second approach is 'cleaner'.... but probably executed wrong...

EDIT2:

Wait. I just realized something new that confuses me even more... is *pntr a int16 or int8? The spi_write is only going send a byte at a time...

ahhhh crap. I give up....
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed Apr 04, 2007 6:00 pm     Reply with quote
You have a pointer to a 16-bit word. All you want to do is extract
the low and high bytes.
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Wed Apr 04, 2007 6:02 pm     Reply with quote
I was just going to add another edit with that conclusion.... it just hit me.

Thanks.

John
jecottrell



Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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PostPosted: Wed Apr 04, 2007 10:22 pm     Reply with quote
PCM,

Can you grade my work? I'm not at PC where I can test my code, but I'd still like to get some feed back on my approach. Specifically, the order of operations/parenthesis grouping in the increment/shift operation and is there a cleaner way to read and combine the two int8s into an int16?

Thanks,

John

Code:
void write_int16_seq_fram(int16 start_addr, int16 *pntr, int16 count)
{
   if(start_addr + (count * 2) <= FRAM_SIZE)
   {
      //setup_spi(SPI_MASTER | SPI_MODE_0_0 | SPI_CLK_DIV_4);
      output_low(FRAM_CS);       //select FRAM
      spi_write(WREN);           //enable writes, required prior to WRITE cmd
      output_high(FRAM_CS);      //de-select FRAM, required between each op-code
      delay_cycles(1);           //ensure compiler doesn't remove the pin toggle
      output_low(FRAM_CS);       //re-select the FRAM
      spi_write(WRITE);          // send the WRITE op-code
      spi_write(start_addr);     //send the low byte of the address
      spi_write(start_addr>>8);  //send the high byte of the address
      do
      {
         //restart_wdt();        //uncomment if slow speeds
         spi_write(*pntr);
         spi_write((*pntr++) >> 8);
      } while(--count);
      output_high(FRAM_CS);      //de-select FRAM
   }
}

void read_int16_seq_fram(int16 start_addr, int16 *pntr, int16 count)
{
   int8  value_low;
   int8  value_hi;
   
   if(start_addr + (count * 2) <= FRAM_SIZE)
   {
      output_low(FRAM_CS);       //re-select the FRAM
      spi_write(READ);          // send the WRITE op-code
      spi_write(start_addr);     //send the low byte of the address
      spi_write(start_addr>>8);  //send the high byte of the address
      do
      {
         //restart_wdt();        //uncomment if slow speeds
         value_low = spi_read(0);
         value_hi  = spi_read(0);
         *pntr++   = make16(value_hi, value_low);;
      } while(--count);
      output_high(FRAM_CS);      //de-select FRAM
   }
}



EDIT:

OK. Following 'Practical C's suggestion, I'll stick with clear coding as opposed to trying to be slick (which I'm not....)

Code:

         spi_write(*pntr);
         spi_write(*pntr >> 8);
         pntr++;

         value_low = spi_read(0);
         value_hi  = spi_read(0);
         *pntr     = make16(value_hi, value_low);
         pntr++;
PCM programmer



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Posts: 21708

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PostPosted: Wed Apr 04, 2007 11:41 pm     Reply with quote
Quote:

spi_write(READ); // send the WRITE op-code
spi_write(start_addr); //send the low byte of the address
spi_write(start_addr>>8); //send the high byte of the address

Quote:

spi_write(WRITE); // send the WRITE op-code
spi_write(start_addr); //send the low byte of the address
spi_write(start_addr>>8); //send the high byte of the address

In both your read and write routines above, you're sending the LSB
of the address first. Figures 9 and 10 of the data sheet (on page 8)
show that the MSB of the address should be sent first, and then the LSB.

http://www.ramtron.com/lib/literature/datasheets/Errata004_25x256.pdf
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