write response in AXI

[sun_ray]

What is the benefit of the write response channel in AXI protocol? How does it help? We know that we have WLAST, RLAST signals also.

 

[sharath666]

WE need to know whether the transaction has been sucessfull or not. That is why we have the response channel. It will indicate either OK or error at the end of the transaction.

 

[sun_ray]

WE need to know whether the transaction has been sucessfull or not. That is why we have the response channel. It will indicate either OK or error at the end of the transaction.

But that response could also be implemented inside the write address channel where WLAST signal also is present after write is completed for on write transaction.

Even for read the response is sucessfull or not, the RRESP happens in read address channel. Why is their a requirement for a separate channel named write response for this?

Regards

 

[sharath666]

For writes, Wlast is an indication from the master indicating the last data in the write operation. But u need some indication from the slave whether it went fine.

 

[sun_ray]

For writes, Wlast is an indication from the master indicating the last data in the write operation. But u need some indication from the slave whether it went fine.

I understand that. But my query is that we can put this write response also in write address channel. What is the need of putting the write response in a separate channel. If we see the read response, it does not happens in a separate channel, the read response happens in read address channel only.

Regards

 

[sharath666]

Can u tell me how can you put write response in address channel?

 

[sun_ray]

The same way read response can be put in the address channel?

Regards

 

[arjun2145]

What is the benefit of the write response channel in AXI protocol? How does it help? We know that we have WLAST, RLAST signals also.

Hi Sunray,

As AXI supports outstanding transactions, for a write transaction the response would come for the entire burst not for each beat.

so, WLAST indicates the last beat of the transaction. WLAST/RLAST does not give any response information of a transaction.

For a read transaction, the response from the slave should be for every beat even it is error or okay the transaction proceeds.

So, read response will be issued for each beat from the slave saying the completion of the transaction.So, it comes with read data channel. But a write response can come at any time with WID.

 

[mr_vasanth]

The same way read response can be put in the address channel?

Regards

AXI has 5 channels
1. Write addr channel
2. Write data channel
3. Write resp channel
4. Read addr channel
5. Read data channel

addr channel carries addr and control information.

When you do a read transaction to a slave, the slave will combine the read response along with data and give it to the master.

The problem with write data channel is, if you are going to the block the write data channel from sending a new data to the salve until a response comes from the slave, your through put will reduce. Keeping write response in a separate channel will help to gain more through put. If master gets an ERROR response from slave, it will use that information to resend the data to the slave.

Basically the architecture tries to keep the MASTER to SLAVE and SLAVE to MASTER path independent.

Response is never put in the address channel either in WRITE transfer or READ transfer.