How to Initialize the Absolute Position on the PMAC

1. The pmac lack a command to directly initialize the axis's absolute value.
   PMAC assumes the AbsPosValue is captured in memory and the '$*' command will 
   set the axis' position. Since TCS3 will have the linux host set the apos, 
   we will  write the APE to pmac RAM and issue the '$*' command.

2. I-variable setup

   I195=$a00000    ; ape value is a Signed 32-bit word
   I110=$f81       ; ape value is located at y:$f81,y:$f82

   I295=$a00000    ; ape value is a Signed 32-bit word
   I210=$1001      ; ape value is located at y:$1001,y:$1002

   Ixx95 (position format) is set:
      bit    23  0x0080 0000 equals  0x1 for signed values.
      bit 16-21  0x002f 0000 equals 0x20 for 32-bits data value.

   Ixx10 (position address) holds the address of the data:

   Ref: Ixx95 I-variable reference in Turbo PMAC Software Reference.


3. The setup files contains these values:

   ;------------------------------------------------------------------------
   ; apv related setup. See notes/apos_initialize.txt documentation
   ;-----------------------------------------------------------------------
   M3100->Y:$000f81,0,24,U     ; low 24-bits for 32-bit APE position (motor1)
   M3101->Y:$000f82,0,24,U     ; high 8-bits for 32-bit APE position (motor1)

   M3200->Y:$001001,0,24,U     ; low 24-bits for 32-bit APE position (motor2)
   M3201->Y:$001002,0,24,U     ; high 8-bits for 32-bit APE position (motor2)

   I195=$a00000    ; ape value is a Signed 32-bit word
   I110=$f81       ; ape value is located at y:$f81,y:$f82

   I295=$a00000    ; ape value is a Signed 32-bit word
   I210=$1001      ; ape value is located at y:$1001,y:$1002

4. Example (setting motor 1 to -8388609, or 0xff7f ffff):

   M3100=$7fffff
   M3101=$ff 
   $*

5. The pm_apos_set() function in pm.c will set the apos for the tcs3.
   This should be execute only in idle mode.