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convert between CRC and the bytes comprising it manually to avoid endianness issues

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This commit is contained in:
marschap
2006-09-09 20:12:38 +00:00
parent e234c49db9
commit ee1e5c967f
2 changed files with 16 additions and 16 deletions
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server/drivers/CFontz633io.c
+15 -12
View File
@@ -173,14 +173,18 @@ void send_zerobyte_message(int fd, unsigned char msg)
static void
send_packet(int fd, COMMAND_PACKET *out, COMMAND_PACKET *in)
{
unsigned char CRC[2];
write(fd, &out->command, 1);
write(fd, &out->data_length, 1);
if (out->data_length > 0)
write(fd, out->data, out->data_length);
/* calculate & send the CRC */
out->crc.as_word = get_crc((unsigned char *) out, out->data_length + 2, 0xFFFF);
write(fd, out->crc.as_bytes, 2);
/* calculate & send the CRC: convert to bytes manually to avoid endianess issues */
out->crc = get_crc((unsigned char *) out, out->data_length + 2, 0xFFFF);
CRC[0] = out->crc & 0xFF;
CRC[1] = (out->crc >> 8) & 0xFF;
write(fd, CRC, 2);
/**** TEST STUFF ****/
// print_packet(out);
@@ -512,17 +516,16 @@ check_for_packet(int fd, COMMAND_PACKET *in, unsigned char expected_length)
for (i = 0; i < in->data_length; i++)
in->data[i] = PeekByte(&receivebuffer);
//Now move over the CRC.
in->crc.as_bytes[0] = PeekByte(&receivebuffer);
in->crc.as_bytes[1] = PeekByte(&receivebuffer);
//Now check the CRC.
//Now move over the CRC: convert CRC bytes to CRC manually to avoid endianness issues
in->crc = PeekByte(&receivebuffer);
in->crc |= PeekByte(&receivebuffer) << 8;
//Compute the expected CheckSum
testcrc = get_crc((unsigned char *) in, in->data_length+2, 0xFFFF);
if (in->crc.as_word == testcrc) {
//This is a good packet. I'll be horn swaggled. Remove the packet
//from the serial buffer.
//Now check the CRC.
if (in->crc == testcrc) {
//This is a good packet. Remove the packet from the serial buffer.
AcceptPeekedData(&receivebuffer);
//Let our caller know that incoming_command has good stuff in it.
/* print_packet(&outgoing_response); */
@@ -535,7 +538,7 @@ check_for_packet(int fd, COMMAND_PACKET *in, unsigned char expected_length)
*/
GetByte(&receivebuffer);
/* fprintf(stderr, "###: Wrong CheckSum. computed/real %04x:%04x \n",
testcrc, incoming_command.crc.as_word); */
testcrc, incoming_command.crc); */
return(TRY_AGAIN);
}
@@ -560,6 +563,6 @@ print_packet(COMMAND_PACKET *packet)
for (i = 0; i < packet->data_length; i++)
fprintf(stderr, " %02x", packet->data[i]);
fprintf(stderr, " ] %02x %02x .\n", packet->crc.as_bytes[0], packet->crc.as_bytes[1]);
fprintf(stderr, " ] %02x %02x .\n", packet->crc & 0xFF, (packet->crc >> 8) & 0xFF);
}
server/drivers/CFontz633io.h
+1 -4
View File
@@ -95,10 +95,7 @@ typedef struct {
ubyte command;
ubyte data_length;
ubyte data[MAX_DATA_LENGTH+1];
union {
unsigned char as_bytes[2];
word as_word;
} crc;
word crc;
} COMMAND_PACKET;