Re: [avr-libc-dev] XMEGA hardware CRC calculation

[Bob Paddock]

> I have no idea why the Xmega should be so slow other than your choice of
> the checksum/CRC algorithm.

Right now I'm using the AVR-LibC XMODEM-CRC, for historical reasons
rather than mathematical reasons.

Make file snippet:
        mv $(OBJDIR)/$@ $(OBJDIR)/$(TARGET).org.hex
        srec_cat $(OBJDIR)/$(TARGET).org.hex -Intel -Little_Endian_CRC16 -max
$(OBJDIR)/$(TARGET).org.hex -Intel -Cyclic_Redundancy_Check_16_XMODEM
-Fill 0xFF -OVER $(OBJDIR)/$(TARGET).org.hex -Intel -Output
$(OBJDIR)/$(TARGET).hex -Intel

Program Snippet (Don't have the newer _u32 sources at hand right now):
  for( crc_u16 = i = 0; i < flash_end_u16; i++)
    {
       byte_u8 = pgm_read_byte( i );
       crc_u16 = _crc_xmodem_update( crc_u16, byte_u8 );
    }

>  If it *is* the speed of reading flash, I
> would be, well, surprised.  After all, you *run* from that flash, right?

Not exactly in the case of the XMega.

The XMega has a separate memory controller for the different
categories of memories to access read or write from them, which is
different than running from Flash.




-- 
http://blog.softwaresafety.net/
http://www.designer-iii.com/
http://www.wearablesmartsensors.com/