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Altera_Forum
Honored Contributor I
786 Views

ALTGX byte ordering problem

Hello, 

I am using two stratix II signal integrity development kits, and try to communicate between them using the ALTGX megacore. I am using it in 16-bit width. 

 

I am experiencing a problem with the order of the bytes - I send two words, i.e. "AABB", "CCDD" but the receiver side receives "DDAA", CCBB" or something similar. 

 

What could be the problem? 

 

more details: 

protocol - basic, no loopback. 

opration mode - receiver and transmitter 

data rate - 624MPBS 

word alignment: sync state machine 

word alignment width: 10 

word alignment pattern: 17c 

8b/10b mode: normal 

 

Thanks!
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2 Replies
Altera_Forum
Honored Contributor I
50 Views

 

--- Quote Start ---  

Hello, 

I am using two stratix II signal integrity development kits, and try to communicate between them using the ALTGX megacore. I am using it in 16-bit width. 

 

I am experiencing a problem with the order of the bytes - I send two words, i.e. "AABB", "CCDD" but the receiver side receives "DDAA", CCBB" or something similar. 

 

What could be the problem? 

 

--- Quote End ---  

 

 

A wild shot in the dark but maybe you don't have a word reversal problem but a word alignment problem or a bit order problem. Try sending methodical test cases like "96" followed by "D1". If you have a byte order reversal you will get "69" then "1D". If you have a bit order reversal you will get "69" then "8B". 

 

I might be off in my explanation but you get the idea... You have to isolate the problem before you can solve it. It might be as simple as a bit order issue.  

 

David
Altera_Forum
Honored Contributor I
50 Views

I'll give another example which implies it's not bit ordering: 

the transmitter sends "0000", "0220","7C0B","0000" but the receiver receives "2000","0B02","007C"....
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