hi,

Now I am thinking a problem. If there are 5 parameters needed assigned to
the register for example on AMBA-AHB or Wishbone, processor could control
the module via R/W the 5 parameters. Thus, we need to deal with the
register alocation to define the register. It comes up with such many ways
to assign each parameter to a 32-bits wide
register. If A paramater is 1 bit, B is 2 bits, C is 9 bits, D is 7 bits, E
is 16 bits,
should we put as many as bits in one 32-bits register, i.e. to increase the
register density for less register access ? However, the driver needs to
pack or unpack the registers to extract/put the information it need. It
also takes time and slow down the
response time of the driver. What's the generally way to deal with it ? How
to balance it ? Should we divided the 32-bits register as 4 or 8 -bits per
block and just put one parameter to it for easy s/w decode ? For example,

0000000A000000B0000000C as a 32-bits register where A is 1-bit, B is 2
bits, C is 9-bits.

Appreciate for your any comments. Thanks

Nanson

Aloha! Quoting NansonHuang at ITRI.ORG.TW: Har do give a simple answer to that question. It greatly depends on the processor and the compiler, unless you use assembler in which case it's the processor ISA that will set the performance for bit handling. If, for example the register is a control and status register with a fixed set of possible values in the application, you can usually create bitmasks and simply do AND, OR-operations to extract the bits and even perform the set/check operations directly without any packing/unpacking. If you need to convert to, say signed integer values you *might* need to do conversion operations and packing/unpacking, but you might be better off letting the application handle that, keeping the driver simple. Some applications may not need the conversion and would be better off then. -- Med vänlig hälsning, Yours Joachim Strömbergson - Alltid i harmonisk svängning. VP, Research & Development ---------------------------------------------------------------------- InformAsic AB / Hugo Grauers gata 5B / SE-411 33 GÖTEBORG / Sweden Tel: +46 31 68 54 90 Fax: +46 31 68 54 91 Mobile: +46 733 75 97 02 E-mail: joachim.strombergson at informasic.com Home: www.informasic.com ----------------------------------------------------------------------