about scanf retarget in Cortexm3 of SmartFuson of Actel

here, str is defined as an array.for example

unsigned char str[10];

So how do you ensure that the data returned by scanf doesn't exceed 9 characters (or whatever your array size happens to be) ?

Surely, this is a fundamental flaw with using scanf ?!

Try searching the forum for "scanf"...

hi, it is just a test since it is myself who is clicking the keyboard.

I don't know when the PC will point to hardfault handler once defined scanf function is executed.

I had searched "scanf" in this forum and find no similar thread.

Looking forward to help.

thanks.

Fisher

You missed the point!

The point is that scanf is, generally, a Bad Thing to be using in such a situation - there are plenty of threads that illustriate this point.

Did you ever implement success scanf function in Cortexm3 in smartFusion? I guess you didn't. otherwise you will find that those scanf examples found in another thereads don't work in Cortexm3 within smartFusion!

Well known dangerous functions that stands for a large number of buffer overflows in this world includes:
scanf()
gets()
sprintf()
strcpy()

Note that Keil doesn't have the standard gets() but have duplicated the fix from fgets(), i.e. added a size parameter telling the max number of characters that may be handled.

Why not?

Is it really anything specifically to do with Cortex-M3 and/or SmartFusion?

Could you please post your scanf() here?
I know how to retarget to real UART connected to PC via Hypertermial using retarget.c.
However I don't know how to retarget to debug(printf) windows via ITM.

Hello Fisher Cheng,

µVision provides for a CM3/CM4 debug support via ITM (Instrumented Trace Macrocell).
In a debug session the Debug (printf) Viewer window is used to display the debug data.

Direction: Microcontroller -> µVision:
* Characters received via ITM communication channel 0 are written in a printf style to Debug (printf) Viewer window.

Direction: µVision -> Microcontroller:
* variable ITM_RxBuffer is used for data transfer.
* Check if ITM_RxBuffer variable is available (only performed once).
* Read character from Debug (printf) Viewer window.
* If ITM_RxBuffer empty write character to ITM_RxBuffer.

Note: Current solution does not use a buffer mechanism for transmitting the characters.

For my tests (only simulation) I used following code in retarget.c

#include <stdio.h>
#include <rt_misc.h>
#include "a2fxxxm3.h"

#pragma import(__use_no_semihosting_swi)

volatile int ITM_RxBuffer = ITM_RXBUFFER_EMPTY;       /* used for Debug Input */

struct __FILE { int handle; };
FILE __stdout;
FILE __stdin;


int fputc(int ch, FILE *f) {
  return (ITM_SendChar(ch));
}

int fgetc(FILE *f) {                /* blocking */
  while (ITM_CheckChar() != 1);
  return (ITM_ReceiveChar());
}

int ferror(FILE *f) {
  /* Your implementation of ferror */
  return EOF;
}

void _ttywrch(int ch) {
  ITM_SendChar(ch);
}

void _sys_exit(int return_code) {
label:  goto label;  /* endless loop */
}

Do not use MicroLib if you are using scanf(..)

Best Regards,
Martin Günther

Hello Martin Günther,

Thank you very much for your help. I add your retarget.c into my project and use following codes:

volatile unsigned char str='\0';
main()
{
  for (;;)
  {
    scanf("%s\n",&str);
    ITM_SendChar(str);
  }
}

I connect A2F dev kit to PC using ulink2 first.
when the program runs in flash target, I place mouse in debug(pringf) windows and then click the key "p" in the keyboard and find :

(1) no character displayed in debug(pringf) windows
(2) when I open memory window 1 and try to observe it using &str commander, I still find that the data is always 0

it seems that no character from Debug (printf) Viewer window is read to ITM_RxBuffer.

Could you please post your test codes here? can scanf() be used in simulation mode only? thanks a lot.

Fisher Cheng

So all do ever do is to get a single string for each input line? Why then don't you use the gets() function, that (in Keils edition) takes a parameter specifying the size of your buffer?

But the worst problem - str is expected to be a string. But your declaration is a character. Taking the address of the character and send into sprintf() means that sprintf() only have a valid if it is expected to retrieve a zero-length string (i.e. a string only storing the termination character).

You must definitely need to make:

enum {
    BUF_SIZE = 64,
};
char str[BUF_SIZE];

Now you have a buffer that can fit 0 to 63 characters + a termination.

And with gets() you can send BUF_SIZE as parameter, making sure that gets() does never allow you to overflow the buffer.

Hello Fischer Cheng,

I only tested the code using the uVision simulator. But if I get a SamrtFusion board I will test it of course using real HW.

I used the following test code:

#include <stdio.h>
#include "a2fxxxm3.h"                   /* A2FxxxM3x definitions              */



volatile uint32_t msTicks;                            /* counts 1ms timeTicks */
/*----------------------------------------------------------------------------
  SysTick_Handler
 *----------------------------------------------------------------------------*/
void SysTick_Handler(void) {
  msTicks++;                        /* increment counter necessary in Delay() */
}

/*------------------------------------------------------------------------------
  delays number of tick Systicks (happens every 1 ms)
 *------------------------------------------------------------------------------*/
__INLINE static void Delay (uint32_t dlyTicks) {
  uint32_t curTicks;

  curTicks = msTicks;
  while ((msTicks - curTicks) < dlyTicks);
}


/*----------------------------------------------------------------------------
  MAIN function
 *----------------------------------------------------------------------------*/
int main (void) {
  FILE *dbgIn;
  unsigned char c;
  unsigned char str[20];


  SysTick_Config(SystemCoreClock / 1000);

  printf ("Example demonstrating CMSIS Debug Functions\r\n\r\n");

  while(1) {
    printf ("Press a key. ");
    c = fgetc(dbgIn);
    printf ("\r\n");
    printf ("You pressed '%c'.\r\n\r\n", c);

    Delay(10);

    printf ("Enter string (press Return to finish) ");
    scanf("%s", str);
    printf ("\r\n");
    printf ("You entered '%s'.\r\n\r\n", str);

    Delay(10);
  }

}

Best Regards,
Martin Guenther

Hello Martin Günther,

Thank you very much. Yes, It works even in real hardware.

You are so kind.

Have a nice weekend.

Hello Per Westermark and Andrew Neil,

also, Thank a lot for your kindly help.
wish you both a nice weekend.

Best regards,
Fisher Cheng

So how do you ensure that the data returned by scanf doesn't exceed 9 characters (or whatever your array size happens to be) ?

"%9s"

I asked how he did ensure it - not how he could (or should) have ensured it...