Nice library Matt!
Please take a look how this guy implemented an X^8 + X^5 + X^4 + 1 CRC in
DS18B20 library:
function d1w_read_byte_with_CRC( byte in nbre_byte )return bit is
var byte bb = 0, n = 0 , crcbyte = 0 -- ! crcbyte must be set to 0
var bit bb_bit0 at bb : 0
var bit crcbyte_bit0 at crcbyte : 0 , crcbyte_bit2 at crcbyte : 2
var bit crcbyte_bit3 at crcbyte : 3 , crcbyte_bit7 at crcbyte : 7
var bit crcbit
for nbre_byte loop -- 8 bytes for ID, 9 bytes for read temp
d1w_read_byte( bb )
n = n + 1 -- ène byte
if n == 1 then d1 = bb end if -- note d1 to d9 are globals
var
if n == 2 then d2 = bb end if --
if n == 3 then d3 = bb end if --
if n == 4 then d4 = bb end if --
if n == 5 then d5 = bb end if
if n == 6 then d6 = bb end if
if n == 7 then d7 = bb end if
if n == 8 then d8 = bb end if
if n == 9 then d9 = bb end if
-- ---calcul of crc---------------
for 8 loop
crcbit = crcbyte_bit0 ^ bb_bit0
crcbyte = crcbyte >> 1
crcbyte_bit7 = crcbit
crcbyte_bit2 = crcbyte_bit2 ^ crcbit
crcbyte_bit3 = crcbyte_bit3 ^ crcbit
bb = bb >> 1
end loop
-- ---------------------------------
end loop
if crcbyte == 0 then crcbit = true else crcbit = False end if -- crcbyte
must be 0 for crc without error
return crcbit
end function
On Tue, Mar 9, 2010 at 7:11 AM, mattschinkel <[email protected]>wrote:
> I have added a CRC library + Sample for error checking. Please give me
> your thoughts and suggestions.
>
> To be honest, I may not be the best person to create such a library
> since CRC creation must be as fast, and as optimized as possible.
> Please let me know if there is a better way to create CRC data, and to
> verify it. At least I can start this library so others can add to it.
>
> This library so far only has functions for 3-bit CRC, but I am sure
> there are other CRC types needed.
>
> Wikipedia has a list of many popular crc types. It does not however
> show 3-bit which I currently need
> http://en.wikipedia.org/wiki/Cyclic_redundancy_check
>
> I can think of many related things that use CRC, and I believe some of
> your libraries already do CRC?
> USB, sd cards, Ethernet....
>
> I currently need this library to send servo data from master to slave
> since an ISR may occur during transmission.
>
> Matt.
>
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