[USRP-users] Confused about the definition of naming pins in FPGA code

Ashish Chaudhari ashish.chaudhari at ettus.com
Fri Oct 3 19:33:09 EDT 2014

Hi Isen,

The signals that you are looking at are a part of the AMBA AXI4-Stream
Interface [1] that is used widely in the X3x0 design. Several signals have
to come together to form a "stream" and they are not in the same direction.
For instance, if you have an AXI stream going from A to B then you would
have the following signals:
- tdata: Data asserted by A for consumption by B
- tvalid: If asserted then the data on the "tdata" bus is valid
- tlast: If asserted then this is the last word in the burst/packet/frame
- tready: If asserted then B is ready to consume more data from A

tdata, tvalid and tlast go from A->B and tready goes from B->A. Data is
only transferred when tvalid and tready are both asserted. The "i_" and
"o_" prefixes on the data just indicate the direction of the stream where
'i' means input and 'o' means output. For example, i_tvalid refers to the
tvalid signal for the input stream for a particular block, and it should be
an "input" port. Similarly o_tready refers to the tready signal for the
output stream which is also an input port.

Hope that helps clear things up.


*Ashish Chaudhari* | Senior Software Engineer | High Frequency Measurements
- RF
Ettus Research, *A National Instruments Company*
ashish.chaudhari at ettus.com

On Fri, Oct 3, 2014 at 12:27 PM, Isen I-Chun Chao via USRP-users <
usrp-users at lists.ettus.com> wrote:

> Hi
> I am digging into the '*radio.v*' of X310 FPGA code. When I traced it
> into module '*axi_fifo_short*', I am so confused about the definition of "
> *i_tvalid*", "*o_tready*", which are inputs, and "*i_tready*", "*o_tvalid*",
> which are outputs. This four signals are used throughout radio module.
> Also, if the range of the register '*a*' is from 0 to 30, is that mean
> this FIFO (*axi_fifo_short*) is only 31 length?
> Thanks.
> *Best Regards,Isen I-Chun Chao*
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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