标签: checksum

Rule : The reserved ARM interrupt vector location(0x0000 0014) should contain the 2's complement of the check-sum of the remaining interrupt vectors. This causes the checksum of all of the vectors together to be 0. Polynomial: V0 + V1 + V2 + V3 + V4 + Sum + V6 + V7 = 0 Code: void CCalc_nxp_checksumDlg::OnCalc() {  // chose bin file  CString sFilename;  CFileDialog dlg(TRUE);      // open with TRUE, save with FALSE  if(dlg.DoModal() == IDOK) {   sFilename = dlg.GetPathName();   // full path  }   // read 8 interrupt vectors  CFile file;  if(!file.Open(sFilename, CFile::modeRead)) { return; }  int data ;  BYTE str ;  for(int i=0; i8; i++) {   file.Read(str, 4);   data = *(int *)str;  }  file.Close();  // calc checksum  int sum = 0;  for(i=0; i8; i++) {   if(i != 5) { sum += data ; }  }  sum = 0 - sum;  BYTE checksum ;  int *sum_ptr = ∑  BYTE *ptr = (BYTE *)sum_ptr;  for(i=0; i4; i++) {   checksum = *ptr;   ptr++;  }  CString sResult;  sResult.Format("%X %X %X %X", checksum , checksum , checksum , checksum );  GetDlgItem(IDC_EDIT1)-SetWindowText(sResult); } Conclusion: In current most IDE, the interrupt vector checksum can be calculated. But for the other old IDE, we have to calculate the checksum by ourselves. Written by Allen in Shenzhen 2010.12.04

The sample code is to check the correct gprmc format with the last chars, and try to calculate the checksum of gprmc. // parameters: // softuart_revbuf: the whole nmea string with header_char '$' and endchar_char 0x0a // softuart_revbuf_len: the length of this nmea string // return: // TRUE: right format; FALSE: bad string format with error end chars or checksum bool nmea_checksum(U8* softuart_revbuf, U32 softuart_revbuf_len) {             U8 checksum = 0;             U8 sum , nmea_sum ;             // "$GPRMC"             if( (softuart_revbuf =='R') (softuart_revbuf =='M') (softuart_revbuf =='C') ) {                 // check nmea data with length, and '*'0x0d0x0a as endchar                 if( (softuart_revbuf_len10) || (softuart_revbuf !=0x0d) || (softuart_revbuf !='*') ) {                     return FALSE;                                }                                 // checksum                 for(U32 i=1; i(softuart_revbuf_len-5); i++)                     checksum ^= softuart_revbuf ;                 nmea_sum = softuart_revbuf ;                 nmea_sum = softuart_revbuf ;                            copy_2xchar_1xchar(sum, nmea_sum, 1);                 if( checksum != sum ) {                     return FALSE;                 }            }            return TRUE; } Allen Zhan GV-TECH 2010.05.24