[avr-libc-dev] [bug #22355] Feature request: eeprom_read_32 and eeprom_write_32

[Shaun Jackman]

URL:
  <http://savannah.nongnu.org/bugs/?22355>

                 Summary: Feature request: eeprom_read_32 and eeprom_write_32
                 Project: AVR C Runtime Library
            Submitted by: sjackman
            Submitted on: Monday 02/18/2008 at 18:02
                Category: Library
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: libc code
                  Status: None
        Percent Complete: 0%
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any

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Details:

eeprom_read_block and eeprom_write_block product terrible code when used with
a 32-bit variable stored in the register file, since the 32-bit variable must
be first copied to the stack, which usually includes adjusting the
stack-pointer and allocating a frame-pointer, leading to all sorts of ugly
overhead. For this reason, I suggest adding eeprom_read_32 and
eeprom_write_32. Simple definitions of these functions follow.

With the current state of optimization, the line `return (uint32_t)hi << 16 |
lo;' does not produce very tight code. Using a union will produce smaller
code. Alternatively, I would *love* to see the GCC optimizer fixed to make the
shift and or produce tight code, but that's a bigger task.

n.b. I don't have AVR hardware at the moment, so these functions are
untested.

Cheers,
Shaun

uint32_t eeprom_read_32(const uint32_t *src)
{
    const uint16_t *p = (const uint16_t *)src;
    uint16_t lo = eeprom_read_word(&p[0]);
    uint16_t hi = eeprom_read_word(&p[1]);
    return (uint32_t)hi << 16 | lo;
}

void eeprom_write_32(uint32_t *dest, uint32_t value)
{
    uint16_t *p = (uint16_t *)dest;
    eeprom_write_word(&p[0], (uint16_t)value);
    eeprom_write_word(&p[1], value >> 16);
}





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