ok, here we go:

1- The communication path is a nine bit bus connected to two nine bit fifos for two ways transmission.


Please clarify above...do you have a single bidirectional 9bit wide data-path or two unidirectional 9bit-wide data paths?


2-A communication always begin with a command I/O Packet(IP) in which 9th bit is 1. Remaining bits are CRC for the command + the data that follows it and the command itself. Depending on the command some data bytes may follow the command that their 9th bits are zero.


Please explain: What is a command I/O packet? is that a single 9-bit word with the 9th bit set to 1? How do you explain that "the remaining bits are crc for command + data"? You spoke about the 9th bit being set to 1. I then assume that the remaining 8 bits are the CRC. Where is the command?



3-After each IP, the receiver sends an Acknowledged (ACK) if CRC is OK and a not acknowledged(NAK) if CRC is wrong. If the packet is important sender 8051 may waits for an ACK message and resend if it receives a NAK(in the case of glitch). In the ACK and NAK frame they may exchange some status data too.


How long will you wait before you decide that something is wrong if the NACK or ACK does not arrive? How will you know what command has been ACK'd as obviously you do not want to wait until your command as been ack'd for sending the next command.



3-Each 8051 has a variable (Queued IPs) that increments when it sends an IP and decrements when it receives an ACK or NAK message.


What happens if you "miss" an ack? or more than one?




as I said I welcome your technical criticisms and ideas.


see inline remarks above :-)




Regards,


Patrick