//============================================================================ // Copyright 2005, Crystalfontz America, Inc. Written by Brent A. Crosby // www.crystalfontz.com, brent@crystalfontz.com //============================================================================ #include #include #include "cf_typedefs.h" #include "cf_serial.h" #include "cf_packet.h" //------------------------------------------------------------------------------ word get_crc(ubyte *bufptr,word len,word seed) { //CRC lookup table to avoid bit-shifting loops. static const word crcLookupTable[256] = {0x00000,0x01189,0x02312,0x0329B,0x04624,0x057AD,0x06536,0x074BF, 0x08C48,0x09DC1,0x0AF5A,0x0BED3,0x0CA6C,0x0DBE5,0x0E97E,0x0F8F7, 0x01081,0x00108,0x03393,0x0221A,0x056A5,0x0472C,0x075B7,0x0643E, 0x09CC9,0x08D40,0x0BFDB,0x0AE52,0x0DAED,0x0CB64,0x0F9FF,0x0E876, 0x02102,0x0308B,0x00210,0x01399,0x06726,0x076AF,0x04434,0x055BD, 0x0AD4A,0x0BCC3,0x08E58,0x09FD1,0x0EB6E,0x0FAE7,0x0C87C,0x0D9F5, 0x03183,0x0200A,0x01291,0x00318,0x077A7,0x0662E,0x054B5,0x0453C, 0x0BDCB,0x0AC42,0x09ED9,0x08F50,0x0FBEF,0x0EA66,0x0D8FD,0x0C974, 0x04204,0x0538D,0x06116,0x0709F,0x00420,0x015A9,0x02732,0x036BB, 0x0CE4C,0x0DFC5,0x0ED5E,0x0FCD7,0x08868,0x099E1,0x0AB7A,0x0BAF3, 0x05285,0x0430C,0x07197,0x0601E,0x014A1,0x00528,0x037B3,0x0263A, 0x0DECD,0x0CF44,0x0FDDF,0x0EC56,0x098E9,0x08960,0x0BBFB,0x0AA72, 0x06306,0x0728F,0x04014,0x0519D,0x02522,0x034AB,0x00630,0x017B9, 0x0EF4E,0x0FEC7,0x0CC5C,0x0DDD5,0x0A96A,0x0B8E3,0x08A78,0x09BF1, 0x07387,0x0620E,0x05095,0x0411C,0x035A3,0x0242A,0x016B1,0x00738, 0x0FFCF,0x0EE46,0x0DCDD,0x0CD54,0x0B9EB,0x0A862,0x09AF9,0x08B70, 0x08408,0x09581,0x0A71A,0x0B693,0x0C22C,0x0D3A5,0x0E13E,0x0F0B7, 0x00840,0x019C9,0x02B52,0x03ADB,0x04E64,0x05FED,0x06D76,0x07CFF, 0x09489,0x08500,0x0B79B,0x0A612,0x0D2AD,0x0C324,0x0F1BF,0x0E036, 0x018C1,0x00948,0x03BD3,0x02A5A,0x05EE5,0x04F6C,0x07DF7,0x06C7E, 0x0A50A,0x0B483,0x08618,0x09791,0x0E32E,0x0F2A7,0x0C03C,0x0D1B5, 0x02942,0x038CB,0x00A50,0x01BD9,0x06F66,0x07EEF,0x04C74,0x05DFD, 0x0B58B,0x0A402,0x09699,0x08710,0x0F3AF,0x0E226,0x0D0BD,0x0C134, 0x039C3,0x0284A,0x01AD1,0x00B58,0x07FE7,0x06E6E,0x05CF5,0x04D7C, 0x0C60C,0x0D785,0x0E51E,0x0F497,0x08028,0x091A1,0x0A33A,0x0B2B3, 0x04A44,0x05BCD,0x06956,0x078DF,0x00C60,0x01DE9,0x02F72,0x03EFB, 0x0D68D,0x0C704,0x0F59F,0x0E416,0x090A9,0x08120,0x0B3BB,0x0A232, 0x05AC5,0x04B4C,0x079D7,0x0685E,0x01CE1,0x00D68,0x03FF3,0x02E7A, 0x0E70E,0x0F687,0x0C41C,0x0D595,0x0A12A,0x0B0A3,0x08238,0x093B1, 0x06B46,0x07ACF,0x04854,0x059DD,0x02D62,0x03CEB,0x00E70,0x01FF9, 0x0F78F,0x0E606,0x0D49D,0x0C514,0x0B1AB,0x0A022,0x092B9,0x08330, 0x07BC7,0x06A4E,0x058D5,0x0495C,0x03DE3,0x02C6A,0x01EF1,0x00F78}; //Initial CRC value is 0x0FFFF. register word newCrc; newCrc=seed; //This algorithim is based on the IrDA LAP example. while(len--) newCrc = (newCrc >> 8) ^ crcLookupTable[(newCrc ^ *bufptr++) & 0xff]; //Make this crc match the one's complement that is sent in the packet. return(~newCrc); } //============================================================================ COMMAND_PACKET incoming_command; COMMAND_PACKET outgoing_response; //============================================================================ // send_packet() // // send_packet() will send set the CRC in outgoing_response and send it to // the host. //---------------------------------------------------------------------------- void send_packet(void) { //In order to send the entire packet in one call to "write()", we //need to place the CRC packed against the data. If data_length //happens to be MAX_DATA_LENGTH, then the position of the CRC is //outgoing_response.CRC (like you would expect), but if data_length //is less, the CRC moves into the data area, packed into the first //unused data position. // //Create a pointer to the first unused data positions. word *packed_CRC_position; packed_CRC_position= (word *)&outgoing_response.data[outgoing_response.data_length]; *packed_CRC_position= get_crc((ubyte *)&outgoing_response,outgoing_response.data_length+2,0xFFFF); //command, length, data[data_length], crc, crc cf_SendData((ubyte *)&outgoing_response,outgoing_response.data_length+4); } //============================================================================ // check_for_packet() // // check_for_packet() will see if there is a valid packet in the input buffer. // If there is, it will copy it into incoming_command and return 1. If there // is not it will return 0. incoming_packet may get partially filled with // garbage if there is not a valid packet available. //---------------------------------------------------------------------------- ubyte check_for_packet(void) { cf_Sync_Read_Buffer(); ubyte i; //First off, there must be at least 4 bytes available in the input stream //for there to be a valid command in it (command, length, no data, CRC). if((i=cf_BytesAvail())<4) return(0); //The "peek" stuff allows us to look into the RS-232 buffer without //removing the data. cf_Sync_Peek_Pointer(); //Only commands 0 through MAX_COMMAND are valid. if(MAX_COMMAND<(0x3F&(incoming_command.command=cf_PeekByte()))) { //Throw out one byte of garbage. Next pass through should re-sync. cf_GetByte(); return(0); } //There is a valid command byte. Get the data_length. The data length //must be within reason. if(MAX_DATA_LENGTH<(incoming_command.data_length=cf_PeekByte())) { //Throw out one byte of garbage. Next pass through should re-sync. cf_GetByte(); return(0); } //Now there must be at least incoming_command.data_length+sizeof(CRC) bytes //still available for us to continue. if((int)cf_PeekBytesAvail()<(incoming_command.data_length+2)) //It looked like a valid start of a packet, but it does not look //like the complete packet has been received yet. return(0); //There is enough data to make a packet. Transfer over the data. for(i=0;i