Difference between FIXED and INCR burst in AXI?

Hi Koumoto-san,

Thanks a lot for your helpful reply. With this example, Master behaviour is clear to me.

Similarly during read for the same example then I assume slave will reciprocate the behaviour.

That is it will put all the 4 bytes for ARLENGTH=4 bytes on ARDATA[7:0] of the bus and for INCR on RDATA[7:0], RDATA[15:8], RDATA[23:16] and RDATA[31:24].

Also for ARSIZE equal to bus width I feel there would be no difference from slave side also.

As for this same example bus width=4 bytes slave would 4 bytes for each transaction for both INCR and FIXED.

Are my assumpltions correct kindly let me know.

Best regards,

Chandan

Hi Koumoto-san,

Thanks a lot for your helpful reply. With this example, Master behaviour is clear to me.

Similarly during read for the same example then I assume slave will reciprocate the behaviour.

That is it will put all the 4 bytes for ARLENGTH=4 bytes on ARDATA[7:0] of the bus and for INCR on RDATA[7:0], RDATA[15:8], RDATA[23:16] and RDATA[31:24].

Also for ARSIZE equal to bus width I feel there would be no difference from slave side also.

As for this same example bus width=4 bytes slave would 4 bytes for each transaction for both INCR and FIXED.

Are my assumpltions correct kindly let me know.

Best regards,

Chandan

Hello Chandan,

I think you are basically correct.
I'm interested in the sentences of "Also for ARSIZE equal to bus width I feel there would be no difference from slave side also".
The information which a slave can get will be the same but the interpretation of it will be implementation dependent.
If the slave is a memory device such as SRAM, FIXED and INCR behavior should differ.
Of course, in the case of AxLEN=0 (i.e. 1 burst), they are completely the same.

Best regards,
Yasuhiko Koumoto.

Hello Chandan,

If a slave would act as FIFOs, you are right.

If you are the slave designer, you can interpret the AxBURST according to your convenience.

Best regards,

Yasuhiko Koumoto.

Thanks a lot Koumoto-san.

Regards,

Chandan

Hi Koumoto-san,

Thanks a lot for your kind reply.

By "Also for ARSIZE equal to bus width I feel there would be no difference from slave side also" I was meaning about the activity

seen on bus from slave side only.

Just for the sake of completion I would like to know how the implementation would differ in slave.

For INCR slave would get the starting address=0x0, for AxSIZE=4, 4 bytes of write data on the bus

and store the 4 transfers for AxLENGTH=4 by incrementing internal address to 0x4,0x8 and 0xC

and for FIXED it would store these transfer like a FIFO( for FIXED is supposed to be used for slaves like FIFOs)

But all the 4 transfers would be stored in slave for FIXED transfer also and not be overwritten.

Kindly let me know.

Best regards,

Chandan