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stack problem with mmcsd_load_buffer

 
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Fabrici



Joined: 11 Feb 2013
Posts: 19
Location: Toulouse - France

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stack problem with mmcsd_load_buffer
PostPosted: Wed Mar 06, 2013 11:15 am     Reply with quote
Hello,

I'm using CCS PCD C Compiler, Version 4.140, 7054

I'm currently trying to communicate between a DSPIC33EP256GP506 and a micro SD card. The function "mmcsd_init()" is returning a bad code (MMCSD_ADDR_ERR), so I build a minimal code to try to isolate the problem. Here is my test code :

Code:
#include <33EP256GP506.h>

#FUSES ICSP1   // ICD uses PGC1/PGD1 pins
#FUSES NOJTAG   // JTAG disabled
#FUSES DEBUG   // Debug mode for use with ICD
#fuses NOALTI2C1   // I2C1 mapped to ASDA1/ASCL1 pins
#fuses NOALTI2C2   // I2C2 mapped to ASDA2/ASCL2 pins
#FUSES NOWDT   // No watchdog timer
#FUSES FRC_PLL  //Internal Fast RC oscillator with PLL

#BUILD (STACK=0x1000:0x1200)
#USE delay (clock=50000000)

// Déclarations pour carte SD
#use fast_io(a)
#use fast_io(c)
#define MMCSD_PIN_SCL      PIN_C3      // o
#define MMCSD_PIN_SDI      PIN_A9      // i
#define MMCSD_PIN_SDO      PIN_A4      // o
#define MMCSD_PIN_SELECT   PIN_C12      // o
#include <mmcsd.c>

/////////////////////////
// Programme principal //
/////////////////////////

void main()
{
   int iRes;

   //
   //// Lecture des valeurs dans la carte SD

   iRes = mmcsd_init();

///////////////////////////
//// Boucle principale ////
///////////////////////////

   do
   {

   } while (TRUE); 
}


When I debug the code, everything seems to go well until the last instruction of the mmcsd_init() : r1 = mmcsd_load_buffer(); .

code of the mmcsd_load_buffer() :

Code:
MMCSD_err mmcsd_load_buffer(void)
{
   g_MMCSDBufferChanged = FALSE;
   return(mmcsd_read_block(g_mmcsdBufferAddress, MMCSD_MAX_BLOCK_SIZE, g_mmcsd_buffer));
}


Here, g_mmcsdBufferAddress is set to 0x00000000 . But when I continue to debug :

Code:
MMCSD_err mmcsd_read_block(uint32_t address, uint16_t size, uint8_t* ptr)
{ 
   MMCSD_err ec;
   uint16_t i; // counter for loops
...


address has been changed to 0x20082008 .... and code will exit with MMCSD_ADDR_ERR.

I'm not fluent with assembler language, but I hope it will help : here are some parts of the .lst file :

Code:
....................    return(mmcsd_read_block(g_mmcsdBufferAddress, MMCSD_MAX_BLOCK_SIZE, g_mmcsd_buffer));
0053A:  PUSH    1402
0053C:  POP     140A
0053E:  PUSH    1404
00540:  POP     140C
00542:  MOV     #200,W4
00544:  MOV     W4,140E
00546:  MOV     #1202,W4
00548:  MOV     W4,1410
0054A:  CALL    46C


I'm a bit surprised with the adresses of the push and pop, which seems to not be in the stack, but as I said before I'm not very fluent in assembler language.

Has anybody encountered this kind of problem ?

Best regards

Fabrice
Fabrici



Joined: 11 Feb 2013
Posts: 19
Location: Toulouse - France

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PostPosted: Thu Mar 07, 2013 11:56 am     Reply with quote
Looking at the .sym file, I was surprised to see same address allocated to different symbols involved in my problem :

1408 mmcsd_init.i
1409 mmcsd_init.r1
140A mmcsd_crc_on_off.crc_enabled
140A-140D mmcsd_set_blocklen.blocklen
140A-140D mmcsd_read_block.address
140E-140F mmcsd_read_block.size
1410-1411 mmcsd_read_block.ptr
1412 mmcsd_read_block.ec

But maybe this is a misunderstanding on my part. Could someone explain to me this assignment ?

Best regards,

Fabrice
Ttelmah



Joined: 11 Mar 2010
Posts: 19343

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PostPosted: Thu Mar 07, 2013 12:54 pm     Reply with quote
That is quite normal.
Variables form a 'tree'. The bottom layer is the global variables. Then static variables. Then local variables in main, then local variables in each function, and so on as functions call functions.
A function at the top of the tree uses a variable in a memory location. When it exits, this memory is no longer in use, and another function at the same level can re-use the same memory. This is why it is vital to never 'assume' that a variable will hold it's value (and to declare as static if you want it to do so).
Memory is re-used, and several variables in different routines can use the same area. The key is (of course), that functions that call other functions, cannot have an area re-used by routines that it calls.
Your problem has come up not that long ago. If I remember, I tried the code, duplicated the problem, and fixed it, and posted this. I can't remember what it was and on a different machine, so can't look up my notes. A search should find the thread. Was it the one where the functions required ANSI mode?. I think it might be.

Best Wishes
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