How to create a look up table for a RAM application

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.

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 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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