How to write the blank room?

[Altera_Forum]

I use two separate pathway to translate data to two separate FIFO, then with TDMA style, the data of the two separate pathway is written to a bus. 

My problem is every frame of the two pathway-data is all 32byte,the frame of the bus data is 128byte,when i write the two to the bus, it leaves 64byte blank room(128-32-32=64). How to deal with the blank room? write 0 and 1 or anything others?  Thanks very much.

[Altera_Forum]

If I understand correctly, your transmitting more data than you're using. It really depends on what your requirements are: 

- Ease - Just leave it as is. This may be 0s, but might be a re-transmit of what you already did. This is also probably the least amount of logic - Power - Having it drive a constant is best - DC/Edge requirements - Some protocols, usually CDR require a certain density of edges, and/or a certain DC balance over time. I'm sure you'd already know if you had this requirement, but just mentioning it - Reliability - You could retransmit it and compare to check for errors. You could encode/decode the data, which usually requires overhead. You could interleave, etc. - Increase bandwidth of data or use it for something else. Many systems will use as much bandwidth as they can get. Anyway, just some ideas. Most likely just tie it to 0, but it's hard to say without more info.

[Altera_Forum]

Thanks very much. Rysc. 

The rate of two pathway data changes from 2~8M. Of course , the formats of the frame change, too. As the pictures I attached. - Increase bandwidth of data or use it for something else. Many systems will use as much bandwidth as they can get. Here the bandwidth of data is alterant,.When the rate of them two is 2M , the down_frame will leave some blank room, otherwise, such as 8M, there will be no blank bit-room left. - Power - Having it drive a constant is best. I can't have it drive a constant ,because I must avoid the bits in the frame is same with the constant .A bit harder to control. I use LPM_bustri to write the two separate pathway to bus. When blank room exists, data on the bus is "zzzz". Now the problem changes into the "zzzz" state.Does it work proper?:confused: