What are the cases when handshaking is preferred over FIFO?

[khaila]

Supposed a Data transferred between two clock domains.
In this case we have two choices for avoiding metastability:
1. Using FIFO.
2. Handshaking.

My question is:
What is the cases that handshaking is preferred than FIFO???


Khalil.

 

[WzWzWz]

Handshaking vs FIFO

Async FIFO is for multi-width data transfer, and this FIFO acts as the same function with normal FIFO.
Handshaking is used for control signal, usually for 1 or two bits signals which cross two clock domain.

 

[asicengineer1]

Handshaking vs FIFO

well, lets say i've this scenario. i've a async.fifo with a depth of 256. so, my pointers will have a minimum width of [7:0] . in this case, my pointer is multi-bit. so, how can i transfer the pointer info. from the write-clock domain to the read-clock domain ?

 

[rjainv]

Re: Handshaking vs FIFO

well, lets say i've this scenario. i've a async.fifo with a depth of 256. so, my pointers will have a minimum width of [7:0] . in this case, my pointer is multi-bit. so, how can i transfer the pointer info. from the write-clock domain to the read-clock domain ?

Gray-encode your pointers and just pass all 8 bits through 8 synchronizers.

 

[asicengineer1]

Handshaking vs FIFO

would it be possible to use handshake mechanism there, instead of synchronizers ?

 

[rjainv]

Re: Handshaking vs FIFO

would it be possible to use handshake mechanism there, instead of synchronizers ?

if you are crossing async clock boundaries, you need synchronizers.
Even any handshake protocol needs to synchronize the control signals going back n forth...

 

[darylz]

Handshaking vs FIFO

If the data is essetially continuously, you cannot avoid to use a FIFO.

 

[subramanyam]

Re: Handshaking vs FIFO

Hii,

The performance of the system when using HANDSHAKING will be less as the Tx will send the next data only after receiving the acknowledgement from the Rx for the previous data . In this case , there will be synchronizers used for the request(Tx to Rx) and ack (Rx to Tx) control signals which also account for the more delay.

So, When u need higher performance and u can afford for more hardware in ur design, u can use FIFO. Other wise u can go for Handshaking where u can use very less hardware.

Best regards,
subbu.

 

[naveenkrishnan]

Re: Handshaking vs FIFO

The best paper ever written on async fifo design is available at http://www.sunburst-design.com/papers/CummingsSNUG2002SJ_FIFO1.pdf

Please read this one... It will be the best effort in your career.

Naveen
www.vlsiforum.com