Re: Clarification for Data_Length...

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Posted by Michael van Dam on February 03, 1998 at 18:44:24:

In Reply to: Re: Clarification for Data_Length... posted by Jim on February 03, 1998 at 14:58:08:

: : : Can someone clarify what 'send "Data_Length copies of the Data Value' means?
: : : Say you have 2 bytes of data to send.
: : : I will denote the 2nd byte of data as simply 2 and the first byte of data as 1
: : : Which one of the following is the correct order :

: : : 2-2-1-1

: : : or

: : : 2-1-2-1

: : :
: : : ???

: : : Thanks.
: : : Jim

: : The intent was to make the lab simpler. You only have two variables, the
: : Data Value (1 byte) and the Data Length (number of bytes). So if the data
: : value is A, and the data length is 4, you should send AAAA.

: Yes, but in the lab, the data size can be from 0 - 1023 bytes, also the
: variable data_length was specified to range from 1-8. Also since we send data
: from lsb to msb, and bytes from msb_byte to lsb_byte, then its important to make
: the distinction of these variables.
: for example, lets say data_size = 3 and data length = 2. Our data is ABC, also
: I will denote x' meaning the order reversal of byte x.

: The questoin i have is what does the data look like when you send it out?

: I claim that the answer could possibly be :

: A'-B'-C'-A'-B'-C'

: however, I can alternatively say the answer could be

: A'-A'-B'-B'-C'-C'

: in which case the original hypothesis is incorrect.

: Hope this helps!
: Allan

Let me try to clear up the confusion here.

In the REAL USB specification, there is a parameter 'data_size' which
specifies how big the data portion of the packet can be. There is no
'data_length' or 'data_value' in that specification.

To simplify the lab, the parameters 'data_length' and 'data_value' were
introduced to REPLACE 'data_size'. There is no 'data_size' in the lab.

So, in the REAL USB protocol, our data portion consists of up to 1023
"arbitrary" bytes. In the lab, our data consists of 1 to 8 copies
of the same BYTE, 'data_value'. ('data_length' tells us exactly how
many copies to send, ie. 1, or 2, ... or 8).

[Looking at this another way, 'data_size', as used in your above
discussion, is always equal to ONE in the lab.]

Hope this helps...
Mike

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Re: Clarification for Data_Length... Jim 23:03:08 2/03/98 (0)

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: : : : Can someone clarify what 'send "Data_Length copies of the Data Value' means? : : : : Say you have 2 bytes of data to send. : : : : I will denote the 2nd byte of data as simply 2 and the first byte of data as 1 : : : : Which one of the following is the correct order : : : : : 2-2-1-1 : : : : or : : : : 2-1-2-1 : : : : : : : : ??? : : : : Thanks. : : : : Jim : : : The intent was to make the lab simpler. You only have two variables, the : : : Data Value (1 byte) and the Data Length (number of bytes). So if the data : : : value is A, and the data length is 4, you should send AAAA. : : Yes, but in the lab, the data size can be from 0 - 1023 bytes, also the : : variable data_length was specified to range from 1-8. Also since we send data : : from lsb to msb, and bytes from msb_byte to lsb_byte, then its important to make : : the distinction of these variables. : : for example, lets say data_size = 3 and data length = 2. Our data is ABC, also : : I will denote x' meaning the order reversal of byte x. : : The questoin i have is what does the data look like when you send it out? : : I claim that the answer could possibly be : : : A'-B'-C'-A'-B'-C' : : however, I can alternatively say the answer could be : : A'-A'-B'-B'-C'-C' : : in which case the original hypothesis is incorrect. : : Hope this helps! : : Allan : : Let me try to clear up the confusion here. : In the REAL USB specification, there is a parameter 'data_size' which : specifies how big the data portion of the packet can be. There is no : 'data_length' or 'data_value' in that specification. : To simplify the lab, the parameters 'data_length' and 'data_value' were : introduced to REPLACE 'data_size'. There is no 'data_size' in the lab. : So, in the REAL USB protocol, our data portion consists of up to 1023 : "arbitrary" bytes. In the lab, our data consists of 1 to 8 copies : of the same BYTE, 'data_value'. ('data_length' tells us exactly how : many copies to send, ie. 1, or 2, ... or 8). : [Looking at this another way, 'data_size', as used in your above : discussion, is always equal to ONE in the lab.] : Hope this helps... : Mike

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