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USB Superspeed Peripherals

Anonymous
Not applicable

 Hi

   

reading datasheets sometomes i find the word burst but i cannot figure out the difference between burst and packet. I've found a definition for burst reading the API guide:

   

 

   

The burst size is the minimum

   

number of words of data that will be sourced/sinked across the GPIF interface without further

   

updates of the GPIF DMA flags. The device connected to FX3 is expected to complete a burst

   

that it has started regardless of any flag changes in between. Please note that this has to be

   

set to a non-zero value (burst size is greater than one), when the GPIF is being configured

   

with a 32-bit data bus and functioning at 100 MHz.

   

 

   

but what about a packet ?

   

 

   

Can anyboby help me ?

   

 

   

Regards

   

 

   

Pit

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1 Reply
Anonymous
Not applicable

 Burst is an overloaded word. We use it in both GPIF and USB.

   

 

   

In USB, a packet is just a chunk of data/information that is sent as a single unit. It can contain data you send/receive or it can contain house-keeping information that the bus uses. 

   

A burst (in USB) is just a collection of packets that are sent before an acknowledgement is received from the receiver. For example, if the PC is reading data from an IN endpoint, then the packet sequence will look like this:
t = 0 ACK TP (NumP = 4):
t = 1 DP...
t = 2 DP...
t = 3 DP...
t = 4 DP...

   

This 4 packet collection is a burst. You can read the USB spec for more information.

   

 

   

GPIF bursts are different and are as you described.

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