int
XisbRead (XISBuffer *b)
{
int ret;
if (b->current >= b->end)
{
if (b->block_duration >= 0)
{
if (xf86WaitForInput (b->fd, b->block_duration) < 1)
return (-1);
}
else
{
/*
* automatically clear it so if XisbRead is called in a loop
* the next call will make sure there is data with select and
* thus prevent a blocking read
*/
b->block_duration = 0;
}
ret = xf86ReadSerial (b->fd, b->buf, b->buffer_size);
switch (ret)
{
case 0:
return (-1); /* timeout */
case -1:
return (-2); /* error */
default:
b->end = ret;
b->current = 0;
break;
}
}
if (b->trace)
ErrorF ("read 0x%02x (%c)\n", b->buf[b->current],
isprint(b->buf[b->current])?b->buf[b->current]:'.');
return (b->buf[b->current++]);
}
/*
***************************************************************************
*
* xf86EloGetPacket --
* Read a packet from the port. Try to synchronize with start of
* packet and compute checksum.
* The packet structure read by this function is as follow:
* Byte 0 : ELO_SYNC_BYTE
* Byte 1
* ...
* Byte 8 : packet data
* Byte 9 : checksum of bytes 0 to 8
*
* This function returns if a valid packet has been assembled in
* buffer or if no more data is available.
*
* Returns Success if a packet is successfully assembled including
* testing checksum. If a packet checksum is incorrect, it is discarded.
* Bytes preceding the ELO_SYNC_BYTE are also discarded.
* Returns !Success if out of data while reading. The start of the
* partially assembled packet is left in buffer, buffer_p and
* checksum reflect the current state of assembly.
*
***************************************************************************
*/
static Bool
xf86EloGetPacket(unsigned char *buffer,
int *buffer_p,
int *checksum,
int fd)
{
int num_bytes;
int readable;
Bool ok;
DBG(4, ErrorF("Entering xf86EloGetPacket with checksum == %d and buffer_p == %d\n",
*checksum, *buffer_p));
/*
* Check if there is any data on the serial port to read.
*/
if ((readable = xf86WaitForInput(fd, 0)) < 0) {
Error("System error while checking Elographics touchscreen for available data.");
return !Success;
}
else if (readable == 0) {
return !Success;
}
/*
* Try to read enough bytes to fill up the packet buffer.
*/
DBG(4, ErrorF("buffer_p is %d, Trying to read %d bytes from link\n",
*buffer_p, ELO_PACKET_SIZE - *buffer_p));
SYSCALL(num_bytes = read(fd,
(char *) (buffer + *buffer_p),
ELO_PACKET_SIZE - *buffer_p));
/*
* Okay, give up.
*/
if (num_bytes < 0) {
Error("System error while reading from Elographics touchscreen.");
return !Success;
}
DBG(4, ErrorF("Read %d bytes\n", num_bytes));
while (num_bytes) {
/*
* Sync with the start of a packet.
*/
if ((*buffer_p == 0) && (buffer[0] != ELO_SYNC_BYTE)) {
/*
* No match, shift data one byte toward the start of the buffer.
*/
ErrorF("Elographics: Dropping one byte in an attempt to synchronize: '%c' 0x%X\n",
buffer[0], buffer[0]);
memcpy(&buffer[0], &buffer[1], num_bytes-1);
}
else {
/*
* Compute checksum in assembly buffer.
*/
if (*buffer_p < ELO_PACKET_SIZE-1) {
*checksum = *checksum + buffer[*buffer_p];
*checksum = *checksum % 256;
DBG(4, ErrorF(" 0x%X-->0x%X ", buffer[*buffer_p], *checksum));
}
(*buffer_p)++;
}
num_bytes--;
}
if (*buffer_p == ELO_PACKET_SIZE) {
/*
* Got a packet, validate checksum and reset state.
*/
ok = (*checksum == buffer[ELO_PACKET_SIZE-1]);
DBG(3, ErrorF("Expecting checksum %d, got %d\n", *checksum, buffer[ELO_PACKET_SIZE-1]));
*checksum = ELO_INIT_CHECKSUM;
*buffer_p = 0;
if (!ok) {
ErrorF("Checksum error on Elographics touchscreen link\n");
return !Success;
}
/*
* Valid packet received report it.
*/
return Success;
}
else {
return !Success;
}
}
