xmodem problems

On 02/22/2013 07:24 PM, Jules Richardson wrote: Well... that's confusing! It seems that it's not a particular sequence of data as such; it stalls when the packet checksum byte read from the sender happens to be 19d - which is XOFF. What I don't get is that my packet read code is basically: /// read packet sequence and "anti-sequence" bytes prior to this using byte(3) /// 260 cksum = 0 270 for i = 0 to 127 step 1 280 poke &A000 + i, byte(3) 290 cksum = cksum + db 300 next i 310 cksum = cksum AND 255 320 ckr = byte(3) /// see if computed and read checksums match at this point; send ACK or NAK to the sender accordingly. /// ('byte(3)' is just a blocking call which returns the next byte from the QX10's serial port. The pokes are to an area of mem I set aside for a receive buffer). There's no difference in the way I read packet sequence numbers, packet data, and the checksum byte - it's all done using byte(3) calls - and yet the presence of an XOFF char within the sequence byte (i.e. receiving packet #19) or within the packet's actual data doesn't cause a problem, but it does when #19 happens to be sent as the checksum byte. It's boggling my brain... it seems more like a problem on the sender's side (i.e. the sender is doing something abnormal when sending 19d as a checksum byte that it doesn't do when sending 19d at other times) - but I'm using the stock linux 'sx' command, which I thought had been around for pretty much as long as linux has, and so surely something as fundamental as this would have been found and fixed years ago... cheers Jules