[Lcdproc] Crystalfontz 633/635 Packet Driver Endianness Issue

[Russell Krayer]

diff included here ...


Index: server/drivers/CFontz633io.c
===================================================================
--- server/drivers/CFontz633io.c        (revision 16)
+++ server/drivers/CFontz633io.c        (working copy)
@@ -63,7 +63,21 @@
#define GOOD_MSG 1
#define GIVE_UP 2

+#define LITTLE_ENDIAN   0
+#define BIG_ENDIAN      1

+int machineEndianness()
+{
+    long int i = 1;
+    const char *p = (const char *) &i;
+    if (p[0] == 1)  // Lowest address contains the least significant byte
+        return LITTLE_ENDIAN;
+    else
+        return BIG_ENDIAN;
+}
+
+
+
/* static local functions */
static void send_packet(int fd, COMMAND_PACKET *out, COMMAND_PACKET *in);
static int  get_crc(unsigned char *buf, int len, int seed);
@@ -180,6 +194,12 @@

        /* calculate & send the CRC */
        out->crc.as_word = get_crc((unsigned char *) out, out->data_length + 
2, 0xFFFF);
+       if (machineEndianness()==BIG_ENDIAN)
+       {
+               unsigned char tmp = out->crc.as_bytes[0];
+               out->crc.as_bytes[0] = out->crc.as_bytes[1];
+               out->crc.as_bytes[1] = tmp;
+       }
        write(fd, out->crc.as_bytes, 2);

        /**** TEST STUFF ****/
@@ -513,8 +533,16 @@
                in->data[i] = PeekByte(&receivebuffer);

        //Now move over the CRC.
-       in->crc.as_bytes[0] = PeekByte(&receivebuffer);
-       in->crc.as_bytes[1] = PeekByte(&receivebuffer);
+       if (machineEndianness()==LITTLE_ENDIAN)
+       {
+           in->crc.as_bytes[0] = PeekByte(&receivebuffer);
+           in->crc.as_bytes[1] = PeekByte(&receivebuffer);
+       }
+       else
+       {
+           in->crc.as_bytes[1] = PeekByte(&receivebuffer);
+           in->crc.as_bytes[0] = PeekByte(&receivebuffer);
+       }
        //Now check the CRC.

        //Compute the expected CheckSum



>From: "Russell Krayer" <rkrayer@msn.com>
>To: lcdproc@lists.omnipotent.net
>Subject: [Lcdproc] Crystalfontz 633/635 Packet Driver Endianness Issue
>Date: Sat, 09 Sep 2006 11:10:12 -0400
>
>Hi,
>
>I stumbled onto an issue with endianness running LCDproc 0.5.0 on a ppc box 
>(a big endian machine).  The problem is in CFontz633io.c when working with 
>the CRC.  I have a fix that is working for me and should still work with 
>little endian machines.  Should I send a patch somewhere?  Note, the bug is 
>also in the Crystalfontz example program from Crystalfontz vendor.
>
>Thanks
>Russ
>
>
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