WRITECODE stores wrong 14-bit word values in FlashMEM

[BobPigford]

Hello!

I am using WRITECODE and READCODE at run time in a PIC16F876A. I send in a series of 70 or more words from my PC (none larger than a 14 bit value) and WRITECODE them into upper FlashRAM sequential addresses (not overwriting program memory).

But when I later READCODE the values from memory, some (about 20%) of the values are wrong. The errors do not follow any particular pattern in the memory sequence that I can see.

I know the 14-bit values are being received correctly by the PIC because I send them back out to an LCD for view prior to the WRITECODE instruction. I have confirmed the errors by sending the READCODE values back to the PC and compared them with what was sent.

The PIC16F876A data sheet talks about writing in blocks of 4 words, not crossing page boundaries, and that a write is really an erase-then-write operation, but I thought that PBP took care of all that for WRITECODE and READCODE.

I will be glad to post the code here if needed, but before doing that I need to ask a basic question:

Am I supposed to use ERASECODE before using WRITECODE on a PIC16F876A?

I would appreciate any guidance you can give on this.

Thank you,
Bob Pigford
Newark, Delaware

[peterdeco1]

Hi Bob. I'm not an expert at this but I use 16F872 & '873 a lot. Instead of READCODE and WRITECODE, try using READ and WRITE. I believe you are writing to program memory space instead of eeprom.

[Archangel]

Hi Bob,
Check these 2 links from Melanie:
http://www.picbasic.co.uk/forum/showthread.php?t=137
http://www.picbasic.co.uk/forum/showthread.php?t=545
Should be something in there that is helpful.

[BobPigford]

Hi Bob. I'm not an expert at this but I use 16F872 & '873 a lot. Instead of READCODE and WRITECODE, try using READ and WRITE. I believe you are writing to program memory space instead of eeprom.

To: Peterdeco1
Thanks for the suggestion, but I do want to write to program RAM (flash RAM) because the EEPROM space will be too small for the 2000 words I want to be able to store eventually.

To: Joe S.
I appreciate those links and I have read and re-read the good info from Melanie several times. She still does not clarify the need for a ERASECODE prior to WRITECODE, though. In fact, after previous readings of her posts, I had assumed that I needed just WRITECODE and READCODE and that PBP took care of all the details.

Please send more suggestions. I appreciate all help!
Bob

[Darrel Taylor]

On the 16F87x and 16F87xA series, ERASECODE will not work. In fact, if you try to use the statement, it will generate an error since there isn't a bit called "FREE" in the EECON1 register.

And yes, PBP takes care of most of the details. But there are still some things the user needs to understand first.

As you've already mentioned, with the A version of these chips, you have to write in blocks of 4-words at a time.
Not just any 4 words, they have to be aligned to a physical Flash boundary.

<table><tr><td><img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3294&stc=1&d=123862608 0" /></td><td valign=top>Since you want up to 2k of space, I assume you're starting at the beginning of Flash Page 3 ($1800).

Blocks always start at the address where the 2 lsb's = 0. So in this case the first block is at $1800.

From there you need to write 4-words consecutively. When it does WRITECODE on 1803 (the 4th word), the contents of the Block will be erased automatically, and the new data will be written.

While erasing, the CPU will "Halt" for approx. 4mS. The OSC is still running, Timers are counting (if used) and the USART will continue receiving data. But SERIN(2) or DEBUGIN cannot receive data during that time. It's easy to miss data if not using the USART.<HR>
If you are attempting to READCODE the word that was just WRITECODEd, for verification ... unless all 4 words of that block have been written, you will not get the expected value back.
<hr>
If you are using Interrupts in your program, they should be disabled globally before writing to FLASH. If an interrupt occurs in the middle of a WRITECODE statement, the procedure can be disrupted and no write will happen, or incorrect data may be written.</td></tr></table>

I could probably ramble on for awhile, so if that doesn't point you in a direction, perhaps a peek at the code might shed new light.

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[flotulopex]

Hello Bob,

Even if very risky (and surely very amateur wise), I'm using the program memory in one of my gadgets for months now using the WRITECODE command.

At the start, I used ERASECODE prior to WRITECODE according to this statement:
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3296&stc=1&d=123866553 2">

After lots of tests, I can say that ERASECODE is not making any difference (if not used, I save some memory space).

The only thing I'm sure about is, that WRITECODE will "rewrite" four (4) words at the time (!!!).

[BobPigford]

On the 16F87x and 16F87xA series, ERASECODE will not work. In fact, if you try to use the statement, it will generate an error since there isn't a bit called "FREE" in the EECON1 register.

And yes, PBP takes care of most of the details. But there are still some things the user needs to understand first.

As you've already mentioned, with the A version of these chips, you have to write in blocks of 4-words at a time.
Not just any 4 words, they have to be aligned to a physical Flash boundary.

<table><tr><td><img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3294&stc=1&d=123862608 0" /></td><td valign=top>Since you want up to 2k of space, I assume you're starting at the beginning of Flash Page 3 ($1800).

Blocks always start at the address where the 2 lsb's = 0. So in this case the first block is at $1800.

From there you need to write 4-words consecutively. When it does WRITECODE on 1803 (the 4th word), the contents of the Block will be erased automatically, and the new data will be written.

While erasing, the CPU will "Halt" for approx. 4mS. The OSC is still running, Timers are counting (if used) and the USART will continue receiving data. But SERIN(2) or DEBUGIN cannot receive data during that time. It's easy to miss data if not using the USART.<HR>
If you are attempting to READCODE the word that was just WRITECODEd, for verification ... unless all 4 words of that block have been written, you will not get the expected value back.
<hr>
If you are using Interrupts in your program, they should be disabled globally before writing to FLASH. If an interrupt occurs in the middle of a WRITECODE statement, the procedure can be disrupted and no write will happen, or incorrect data may be written.</td></tr></table>

I could probably ramble on for awhile, so if that doesn't point you in a direction, perhaps a peek at the code might shed new light.

<!-- Attachment 3294 -->

Thank you all!

Ahhh. I see. I will now:
1) Start my WRITECODE at an appropriate address (block start boundary).
2) Make sure that the last of my many consecutive WRITECODE instructions are padded with enough additional WRITECODE instructions to fill the last block completely.
3) If I go back and try to WRITECODE over a previously written address, I must know where it was in that block of addresses, then re-write the adjacent values for a total of 4 WRITECODE instructions to fill that block again.

I will report back!

Thanks again.
Bob

[BobPigford]

Hello all!

Following Darrel Taylor's excellent instructions, I was careful to WRITECODE to 4 word (complete) blocks starting at $1800 (or any other address where the two LSBs are 0's). I still saw wrong stored values. Every 6th address (and a few others) had an error ... VERY strange behavior.

I had been using 12 WORD sized array variables of 3 elements each, stuffing the last 2 variables of each array into memory (WRITECODE). Suspecting that array variables were the culprits, I changed to 36 individual WORD variables along with all the repetitive code required. NOW IT WORKS!

The PBP manual (pg 25) says clearly that "The compiler will assure that arrays, as well as simple variables, will fit in memory before successfully compiling."

My code is about 4100 WORDs in size. It compiled just fine, albiet showing three notes at the bottom of the screen that code page boundaries were being crossed. I had assumed that since the code compiled just fine, that the 3 warnings pertained to the overall size of my code. BUT, perhaps those were warnings that arrays would not work.

BUT why did it still compile OK? Did the PBP compiler let me down?

Makes me wary of using array variables. I need to learn more about this in the future!

Thanks again to all for your help!
Bob Pigford
Newark, Delaware

[Darrel Taylor]

Great! Glad it helped.

Makes me wary of using array variables.

Nothing to worry about there. Arrays work perfectly with PBP.
And yes, PBP makes sure the arrays will fit in a BANK of RAM.

The crossing boundary warnings refer to the FLASH memory used by the program. The same area of memory that you are WRITECODEing to.
Arrays can not cause that warning.

Array indexes always start at 0.
So if you have a word array of 3 elements, the index goes from 0 to 2.
It's easy to forget and try to use 1 - 3, but 3 would be outside of the array, probably a RAM location used by another variable.

PBP does not do any "Range Checking". It's up to you to stay within the bounds of the array.

Just about any good program will use arrays in some form or another.
So yup, time to learn ... then play ... then learn more ...
<br>

[rsocor01]

Darrel,
From reading other posts and other documentation (if I understood them correctly) when using arrays in a pic16fxxx and if the program crosses the memory boundary then that would be looking for trouble. In other words, if you are using arrays all over the place in your program, then your program has to fit in one memory block which is ussually not the case. Otherwise, the program won't work properly.
I personally like arrays. They make your program looks neat and more profesional, but also my programs are usually bigger than 2K.

Any comments on this?

Robert

[Darrel Taylor]

NO! Not true at all.

The size of your program has NO effect on arrays.
Arrays are in RAM, the program is in FLASH.

You may be thinking of the problems that can happen with the BRANCH command if the code is larger than 2K. In which case you need to use BRANCHL.

[BobPigford]

Darrel, et al,

I understand going out of bounds of a dimensioned array, and that arrays start at 0. I believe that my use of array variables was correct, but I will go back and look again. Perhaps I missed something.

I am glad to hear that PBP did not let me down, per se, as array variables are held in RAM and arrays crossing any page boundaries are handled by PBP.

So, I guess I will have to go back and bang out the code with array variables again. It may be a while, but I will report back.

Thanks to all for your help!
Bob Pigford
Newark, DE, USA

[BobPigford]

I am glad to hear that PBP did not let me down, per se, as array variables are held in RAM and arrays crossing any page boundaries are handled by PBP.

Oops. I should not have talked about arrays crossing any boundaries since Darrel reminded me that they are in RAM. Sorry.

Bob

[rsocor01]

Darrel,
I think my confusion comes from the PicBasic Pro Manual, section 4.5, "Arrays".
"Arrays must fit entirely within one RAM bank on 12-bit, 14-bit or pic17cxxx devices."

Yeap, I know the program is not stored in RAM. But, what are the implications of this limit to one RAM bank for arrays? Would it be only the limited number of elements in an array?

Robert

[Darrel Taylor]

But, what are the implications of this limit to one RAM bank for arrays? Would it be only the limited number of elements in an array?

Exactly.

The largest amount of GP ram in a 16F's bank is 96 bytes. (chip dependant)
So the biggest WORD array you can make has 48 elements.

You could have 3 arrays with 48 words, but not all in one.

hth,

[BobPigford]

Hello!

Thanks again to all who pointed out that writing to FlashRAM has to be done in blocks and starting at addresses where the last two bits of address are 00!
That knowledge allowed me to make my program work OK, but not in an efficient way. I could not get array variables to work for me. I ended up creating 36 separate word variables to get the job done.

But, I realized that I had not posted anything about my array variable issues since last April. I am still wondering what I was doing wrong. Please help me better understand array variables.

Below are some snippets of my code that are germane to the issue.

Program background:

My program runs on a PIC16F876A at 20 mHz

At run time, I stuff 14-bit word sized data from a PC into upper FlashRam, then with a switch closure, I change to a routine that reads the words at those addresses and displays them bit-wise. The serial transfer of words and stuffing into FlashRAM works well and I have verified that the correct 14 bit words are correctly placed into FlashRAM.

When I read words from FlashRAM, these words are put into 2 of my array variables for my subsequent bit-wise display.

It helps to "conceptualize" the layout of those array variables like this:

MAX1A[0] MAX2A[0] MAX3A[0] MAX4A[0] MAX5A[0] MAX6A[0]
MAX1B[0] MAX2B[0] MAX3B[0] MAX4B[0] MAX5B[0] MAX6B[0]

MAX1A[1] MAX2A[1] MAX3A[1] MAX4A[1] MAX5A[1] MAX6A[1]
MAX1B[1] MAX2B[1] MAX3B[1] MAX4B[1] MAX5B[1] MAX6B[1]

MAX1A[2] MAX2A[2] MAX3A[2] MAX4A[2] MAX5A[2] MAX6A[2]
MAX1B[2] MAX2B[2] MAX3B[2] MAX4B[2] MAX5B[2] MAX6B[2]

This comprises 12 array variables, each with 3 elements [0, 1, 2].

After I display them (display code not shown - it works well), I move those last 6 words from the last array elements to their left adjacent array variables with a "riffle" routine that also works well (shown in my code snippets below). Then the program loops and repeats reading words from FlashRAM and displaying them until I reach a preset address in upper FlashRAM.

What DOES NOT work is the stuffing of words into the array elements in the last column. Wrong values appear there, and the program slows to a crawl, updating about once every 30 seconds or even longer. When complied, no errors are generated.
But when I use 36 separate word variables in place of the array elements, all works well.

Snippets of my code that apply:

'snippet from my program
'array variables declared
MAX1A   VAR WORD[2]
MAX1B   VAR WORD[2]
MAX2A   VAR WORD[2]
MAX2B   VAR WORD[2]
MAX3A   VAR WORD[2]
MAX3B   VAR WORD[2]
MAX4A   VAR WORD[2]
MAX4B   VAR WORD[2]
MAX5A   VAR WORD[2]
MAX5B   VAR WORD[2]
MAX6A   VAR WORD[2]
MAX6B   VAR WORD[2]

'code loop that gets WORD values from FlashRAM and stuffs it into
'the elements of 2 arrays
    readcode mempntr, MAX6A[0]
    mempntr = mempntr + 1
    readcode mempntr, MAX6B[0]
    mempntr = mempntr + 1
    readcode mempntr, MAX6A[1]
    mempntr = mempntr + 1
    readcode mempntr, MAX6B[1]
    mempntr = mempntr + 1    
    readcode mempntr, MAX6A[2]
    mempntr = mempntr + 1
    readcode mempntr, MAX6B[2]
    mempntr = mempntr + 1
    
'other code that moves word values from one array element to another
'so it can be displayed by other routines, then goes back 
'6 more words, displays them, etc.

Riffle:
  for N = 0 to 2  'move all words to the left for all 3 screens worth of WORDs
    MAX1A[N] = MAX2A[N] : MAX2A[N] = MAX3A[N] : MAX3A[N] = MAX4A[N] : MAX4A[N] = MAX5A[N] : MAX5A[N] = MAX6A[N]
    MAX1B[N] = MAX2B[N] : MAX2B[N] = MAX3B[N] : MAX3B[N] = MAX4B[N] : MAX4B[N] = MAX5B[N] : MAX5A[N] = MAX6B[N]
  next N

There must still be something I do not understand about array usage and syntax under PICBasicPro. Please point me in the right direction with regard to array variables.

Thank you to all who are patient with me and offer to help!
Bob Pigford
Newark, DE, USA

[Dick M]

Looking at 4.5 Arrays in the manual it looks like you need to redefining your element from word[2] to word[3]

[BobPigford]

Looking at 4.5 Arrays in the manual it looks like you need to redefining your element from word[2] to word[3]

Thank you, Dick M. Could it be this simple?
In the manual example in section 4.5 it reads:

" shark VAR BYTE[10]
fish VAR BYTE[8]
The first array location is element 0. In the fish array defined above, the elements are numbered fish[0] to fish[7] yielding 8 elements in total."

Gee, I had previously thought that the highest element would be #7, therefore expecting the highest number element to be used in the VAR definition. After rereading the manual (how many times did I already read the manual on this, yet I missed it), it SURE LOOKS LIKE I HAD IT ALL WRONG!!!!!

Wow, all this struggling. How annoying it will be to find out that I declared my array VARs incorrectly. Of course, it would have been nice if the COMPILER would have reported an error, but I still feel like such a dunce. I will try it again and report back. MANY thanks, Dick M!
Bob

Now I must go back to PBP and try it all again!

[BobPigford]

Well, I checked my understand of dimensioning arrays in other forms of BASIC. In other BASICs,
DIM fish(20)
creates an array of 21 elements (0 through 20). Hence, the source of my confusion.

In PBP:
fish VAR WORD[20] has 20 elements (0 through 19).

Getting smarter as I go.

Bob