How to create a look up table for a RAM application

[Vazquez]

Dear Sir or Madame,

I have a data packet which has a 13 bit field for an USB
application(7bit + 4bit + 1bit + 1bit).


Because of lack of memory I do create a RAM which
has a data input width of only 10 bit. The write address of
the RAM is [4..0], i.e. 32 words á 10 bit.
The words which are written into the RAM
are searched for later (CAM-like function).

The problem: I have to reduce 13 bit to 10 bit without losing the
significance of the 13 bit. But it is not possible to leave out for
example
two bits of the 7bit (usb address) because the enumeration by the host
is not
predictable.

How could I solve this problem?

Thank you very much.

Best regards

Andres Vazquez
G&D System Development

 

[Erez Birenzwig]

You can use a one way hash function to do the reduction.
A CRC is a good example, one can think of others. It will probably not solve
your
space problem though.

Erez.

"Vazquez" <andres.vazquez@gmx.de> wrote in message
news:eee19a7a.0311100448.1577e5c2@posting.google.com...

Dear Sir or Madame,

I have a data packet which has a 13 bit field for an USB
application(7bit + 4bit + 1bit + 1bit).


Because of lack of memory I do create a RAM which
has a data input width of only 10 bit. The write address of
the RAM is [4..0], i.e. 32 words á 10 bit.
The words which are written into the RAM
are searched for later (CAM-like function).

The problem: I have to reduce 13 bit to 10 bit without losing the
significance of the 13 bit. But it is not possible to leave out for
example
two bits of the 7bit (usb address) because the enumeration by the host
is not
predictable.

How could I solve this problem?

Thank you very much.

Best regards

Andres Vazquez
G&D System Development

 

[Hul Tytus]

Assuming the max number of endpoints is known, make another RAM
7 x (max number of endpoints). Use this ram to store the actual endpoint
numbers and change the 7 bit endpoint field in the primary ram to a
bit count in accordance with the max number of endpoints.

For example, if only 4 endpoints, then change the 7 bit field to a 2
bit field and, at enumeration, store the numbers in the smaller ram.

Hul

Vazquez <andres.vazquez@gmx.de> wrote:
: Dear Sir or Madame,
:
: I have a data packet which has a 13 bit field for an USB
: application(7bit + 4bit + 1bit + 1bit).
:
:
: Because of lack of memory I do create a RAM which
: has a data input width of only 10 bit. The write address of
: the RAM is [4..0], i.e. 32 words ? 10 bit.
: The words which are written into the RAM
: are searched for later (CAM-like function).
:
: The problem: I have to reduce 13 bit to 10 bit without losing the
: significance of the 13 bit. But it is not possible to leave out for
: example
: two bits of the 7bit (usb address) because the enumeration by the host
: is not
: predictable.
:
: How could I solve this problem?
:
: Thank you very much.
:
: Best regards
:
: Andres Vazquez
: G&D System Development

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