Subject: [rohc] UDVM register values

From: [email-masked]
Date: Wed, 22 May 2002 13:27:53 -0500

Hi,
  It's not quite clear how UDVM registers (byte_copy_left, byte_copy_right,stack_location etc) are set when memory is allocated and initialized for UDVM. Do they have any default values or UDVM bytecode instructions used for decompression should take care of setting the values for them. 

-Narendra

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From: "Price, Richard" <[email-masked]>
Date: Thu, 23 May 2002 10:00:04 +0100

Hi,

A description of how to initialize the UDVM memory can be found in
Section 7.2:

   The first five 2-byte words are initialized to contain some values
   that might be useful to the UDVM bytecode (Useful Values). Note that
   these values are for information only and can be overwritten when
   executing the UDVM bytecode without any effect on the endpoint. The
   MSBs of each 2-byte word are stored preceding the LSBs.

   Addresses 0 to 5 indicate the resources available to the receiving
   endpoint. The UDVM memory size is expressed in bytes modulo 2^16, so
   in particular it is set to 0 if the UDVM memory size is 65536 bytes.
   The cycles_per_bit is expressed as 2-byte integer taking the value
   16, 32, 64 or 128. The SigComp_version is expressed as a 2-byte value
   as per Section 3.3.2.

   Addresses 6 to 9 are initialized to the length of the partial state
   identifier, followed by the state_length from the retrieved state
   item. Both are expressed as 2-byte values.

   Addresses 10 to 31 are reserved and are initialized to 0 for Version
   0x01 of SigComp. Future versions of SigComp can use these locations
   for additional Useful Values, so a decompressor MUST not rely on
   these values being zero.

   Any remaining addresses in the UDVM memory that have not yet been
   initialized MUST be set to 0.

Since the UDVM registers begin at Address 64, they must be initialized
to 0 as per the above paragraph. The bytecode which is uploaded to the
UDVM will take care of setting the registers to suitable values.

Regards,

Richard

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]
> Sent: Wednesday, May 22, 2002 7:28 PM
> To: [email-masked]
> Subject: [rohc] UDVM register values
> 
> 
> Hi,
>   It's not quite clear how UDVM registers (byte_copy_left, 
> byte_copy_right,stack_location etc) are set when memory is 
> allocated and initialized for UDVM. Do they have any default 
> values or UDVM bytecode instructions used for decompression 
> should take care of setting the values for them. 
> 
> -Narendra
> 
>