need to change CRC peripheral's polynomial

[infoinfo991]

Posted on January 04, 2014 at 03:13

The reference manual for the STM32F4 states that the polynomial for the CRC generator is 0x4C11DB7

I must change it to 0x0B5D0A7D or else my application will not work, as I am spoofing another deviceIs there a trick to calculating an input such that it seems as if my CRC used 0x0B5D0A7D?Is there anyway to change it? I have searched, the FAQ does not help at all.

[lowpowermcu]

Posted on January 04, 2014 at 11:49

Hi Franck,

The polynomial is not configurable in STM32F4 family so you have to do the calculation by software if you have another polynom. PS: The CRC in STM32F3 family has the polynomial configurable.

[Tesla DeLorean]

Posted on January 04, 2014 at 15:43

What are the data and crc shift directions?

Can you provide a couple of example data sets?

[infoinfo991]

Posted on January 04, 2014 at 20:46

I have the example data at the bottom of this page

http://eleccelerator.com/wiki/index.php?title=DualShock_4

[infoinfo991]

Posted on January 04, 2014 at 21:09

Oops I made a mistake, it seems like 0x4C11DB7 will work after all

[Tesla DeLorean]

Posted on January 05, 2014 at 02:36

Yeah, your talking about the result/remainder, not the polynomial. They claim it's the same although I haven't run the math on the STM32, which is kind of backward for a little endian processor.

[Tesla DeLorean]

Posted on January 07, 2014 at 21:24

Ok, so a couple of issues with the STM32 F1/F2/F4 hardware

It shifts in the wrong direction, and consumes 32-bits at a time. You'd need to bit reverse (RBIT) the value before passing it to the hardware, and special case the last 0-3 bytes. There was a

/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/CRC%20computation&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&currentviews=1617

about using the hardware for PKZIP/CRC32 computations. Here is a worked case for a software solution.

/*
Dual Shock 4 CRC Demo - Clive - sourcer32@gmail.com
Data set for example pulled from
http://eleccelerator.com/wiki/index.php?title=DualShock_4
STM32 Thread
[DEAD LINK /public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/need%20to%20change%20CRC%20peripheral%27s%20polynomial&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&TopicsView=https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/AllItems.aspx?Paged%3DTRUE%26p_StickyPost%3D%26p_DiscussionLastUpdated%3D20140105%252020%253a55%253a31%26p_ID%3D36700%26View%3D%257bF47A9ED8%252dE726%252d42BE%252dACED%252d732F13B66581%257d%26FolderCTID%3D0x012001%26PageFirstRow%3D41&currentviews=48]https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=%2fpublic%2fSTe2ecommunities%2fmcu%2fLists%2fcortex%5fmx%5fstm32%2fneed%20to%20change%20CRC%20peripheral%27s%20polynomial&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&TopicsView=https%3A%2F%2Fmy%2Est%2Ecom%2Fpublic%2FSTe2ecommunities%2Fmcu%2FLists%2Fcortex%5Fmx%5Fstm32%2FAllItems%2Easpx%3FPaged%3DTRUE%26p%5FStickyPost%3D%26p%5FDiscussionLastUpdated%3D20140105%252020%253a55%253a31%26p%5FID%3D36700%26View%3D%257bF47A9ED8%252dE726%252d42BE%252dACED%252d732F13B66581%257d%26FolderCTID%3D0x012001%26PageFirstRow%3D41¤tviews=48
cl -Ox dualshk.c
>dualshk
88 Total
75 Payload
0B5D0A7D CRC Encoded
0B5D0A7D
0B5D0A7D
*/
#include <
windows.h
>
#include <
stdio.h
>
//****************************************************************************
DWORD Crc32Byte(DWORD Crc, BYTE Data)
{
int i;
Crc = Crc ^ (DWORD)Data;
for(i=0; i<
8
; i++)
if (Crc & 1)
Crc = (Crc >> 1) ^ 0xEDB88320; // Polynomial used in PKZIP, CRC-32 Right Shifting
else
Crc = (Crc >> 1);
return(Crc);
}
//****************************************************************************
DWORD Crc32ByteBlock(DWORD Crc, DWORD Size, BYTE *Buffer)
{
while(Size--)
Crc = Crc32Byte(Crc, *Buffer++);
return(Crc);
}
//****************************************************************************
DWORD Crc32FastBlock(DWORD Crc, DWORD Size, BYTE *Buffer)
{
static const DWORD CrcTable[] = { // For 0xEDB88320 Polynomial
0x00000000,0x1DB71064,0x3B6E20C8,0x26D930AC,0x76DC4190,0x6B6B51F4,0x4DB26158,0x5005713C,
0xEDB88320,0xF00F9344,0xD6D6A3E8,0xCB61B38C,0x9B64C2B0,0x86D3D2D4,0xA00AE278,0xBDBDF21C };
while(Size--)
{
Crc = Crc ^ (DWORD)*Buffer++;
Crc = (Crc >> 4) ^ CrcTable[Crc & 0x0F]; // Process 8-bits, two rounds of 4-bits
Crc = (Crc >> 4) ^ CrcTable[Crc & 0x0F];
}
return(Crc);
}
//****************************************************************************
// http://eleccelerator.com/wiki/index.php?title=DualShock_4
BYTE TestVector[] = { 0x02,0x15,0x20,0x53,0x00,0x4F,0x00,0x42,0x00, // Header
0xA1,0x11,0xC0,0x00,0x83,0x81,0x7E,0x7E,0x08,0x00,0x3C,0x00,0x00,0x83,0xA2, // Payload
0x07,0xF1,0xFF,0xF9,0xFF,0x04,0x00,0x21,0x03,0x17,0x1F,0x29,0xF9,0x00,0x00,
0x00,0x00,0x00,0x08,0x00,0x00,0x00,0x00,0x80,0x00,0x00,0x00,0x80,0x00,0x00,
0x00,0x00,0x80,0x00,0x00,0x00,0x80,0x00,0x00,0x00,0x00,0x80,0x00,0x00,0x00,
0x80,0x00,0x00,0x00,0x00,0x80,0x00,0x00,0x00,0x80,0x00,0x00,0x00,0x00,0x00,
0x7D,0x0A,0x5D,0x0B }; // CRC32
//****************************************************************************
int main(int argc, char **argv)
{
printf(''%d Total

'', sizeof(TestVector));
printf(''%d Payload

'', sizeof(TestVector) - 4 - 9); // Less 9 byte header, and 4 byte CRC
printf(''%08X CRC Encoded

'', *((DWORD *)&TestVector[sizeof(TestVector) - 4]) );
// Initial value 0xFFFFFFFF, then inverted
printf(''%08

X'',~Crc32ByteBlock(0xFFFFFFFF, sizeof(TestVector) - 4 - 9, &TestVector[9]) );
printf(''%08

X'',~Crc32FastBlock(0xFFFFFFFF, sizeof(TestVector) - 4 - 9, &TestVector[9]) );
return(0);
}