Common Questions About Mano's Simple Machine Projects

Last updated 2002/03/27

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Contents

Notes:

1. Do not use StorageObject's backDoor function

Questions:

1. Is the provided implementation of CIR and CIL broken?

Notes

 
1. StorageObject void backDoor (long x): The StorageObject class does contain a function void backDoor (long x) that allows you to load a value into any storage object. You are not allowed to use this function, as it is a hack that exists for testing. Any use of this function will result in point loss on the lab.
   

Questions

 

1. > It looks like the mano program in ~icsg720/pub/bin.solaris/small_mano
   > might have an error in it when executing CIR/CIL instructions.  After
   > loading a hexadecimal 8001 into AC, CIR yields a 4000 value in AC and
   > CIL yields 0002.  It looks like it's not picking up the 1 bits on the
   > ends when circulating.
   

   The program is correct, Mano's definition of CIR/CIL are different from the standard. What he does is rotate the AC through the E register so...

   Inital          E=0 AC=8001
   after CIR       E=1 AC=4000
   after CIL       E=1 AC=0002
   

   What is happening is the E register is acting like the 17th bit of the AC for purpose of the rotate. So if we start with an E=1...

   Inital          E=1 AC=8001
   after CIR       E=1 AC=C000
   after CIL       E=1 AC=0003
   

   This can be seen in the RTL for the instruction (note that these are all done in parallel):

   CIR     rB(7):  AC <- shrAC, AC(15) <- E, E <- AC(0)
   CIL     rB(6):  AC <- shlAC, AC(0) <- E, E <- AC(15)
   

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