Question

I am working on the Firmware for an embedded USB project. The production programmer I would like to use automatically writes the Serial Number into the device flash memory at a specified memory address. The programmer stores the serial number as Hex digits in a specified number of bytes. For example, if I tell it to store the serial number 123456 at address 0x3C00 my memory looks like this:

0x3C00  -  00
0x3C01  -  01
0x3C02  -  E2
0x3C03  -  40
//(123456 in Hex = 1E240)

The problem is, when my host application reads the serial number from the device it is looking for a unicode char array. So my serial number should be …

{ '1','0',
  '2','0',
  '3','0',
  '4','0',
  '5','0',
  '6','0'}

When the

So in my firmware, which I’m writing in C, is it possible to retrieve the hex serial number from flash, encode it into a unicode char array and store it in a variable in Ram?

Answer 1

If the serial number fits into 32 bits and the platform is big endian and supports Unicode, 32 bit ints and the standard C libraries then this is pretty straightforward as other answers have shown. If the platform has 32 bit ints and 8 bit chars but is little endian and/or doesn’t support Unicode, and if the serial number can vary in length, then the below may be useful, though it’s a little workmanlike.

void extract_serial_number(unsigned char* address, unsigned int bytes, char* buffer) {
    unsigned int value = 0;
    char c, *start = buffer;
    while (bytes--) {                      /* read the serial number into an integer */
        value = value << 8;
        value |= *address++;
    }
    while (value > 0) {                    /* convert to 16 bit Unicode (reversed) */
        *buffer++ = '0' + value % 10;
        *buffer++ = '\0';
        value /= 10;
    }
    *buffer++ = '\0';
    *buffer++ = '\0';
    buffer -= 4;
    while (buffer > start) {               /* reverse the string */
        c = *buffer;
        *buffer = *start;
        *start = c;
        buffer -= 2;
        start += 2;
    }
}