-- old pr_servo_remove_tt --------------------------------------------

1. Cal Delta Drive:

   delta_drive[a] = pr_sign * inverse[a][s] * signal[s]

2. Intergrator

   temp_pr_out[a] = pr_out[a] + (delta_drive[a] * pr_gain)

3.  remove tilt.

   a. Cal TT from DM data:
      tt_dd[a] = tt_sign * (ttdm_inverse[a][s] * temp_pr_out[s] )

   b. Cal pr_out[s] values related only to tiptilt.
      pr_out_tt[s] = input_imat[s][a] * tt_dd[a]

   c. Removes tt component from temp_pr_out[a]
      temp_pr_out[a] = temp_pr_out[a] - (pr_out_tt[a] * pr_gain2)

4.  set actuators

    pout[a] = temp_pr_out[a]

--- new  pr_servo_remove_tt -------------------------------------------

1. Cal Delta Drive:

   delta_drive[a] = pr_sign * inverse[a][s] * signal[s]

2. Intergrator

   temp_pr_out[a] = pr_out[a] + (delta_drive[a] * pr_gain)

3.  remove tilt.

   a. Cal TT Delta Drive:
      tt_dd[a] = tt_sign * (ttdm_inverse[a][s] * temp_pr_out[s] )

   -  save tt_dd[a] for TT_SERVO_DM. if TT_DM is used, don't use pr_out
      since it has TT information removed. 
      TT_DD[a] = tt_dd[a] 

   b. Cal pr_out[s] values related only to tiptilt.
      pr_out_tt[s] = input_imat[s][a] * tt_dd[a]

   c. Removes tt component from temp_pr_out[a]
      temp_pr_out[a] = temp_pr_out[a] - (pr_out_tt[a] * pr_gain2)

4.  set actuators

    pout[a] = temp_pr_out[a]


-- change to tt_servo_dm()  ----------------------------------------------------------

   pr_servo must be on (PR_SERVO_PR, PR_SERVO_PRTT)

   if( PR_SERVO_PR )
   {
      tt_delta_drive[a] = tt_sign * ttdm_inverse[a][s] * pr_out[s]
   }
   else 
   {
      //use saved tt_dm[a] from pr_servo_remove_tt()
      tt_delta_drive[a] = TT_DD[a].
   }

-- feedback ----------------------------------------------------------

   PR_SERVO_PR -> pr_servo()
   PR_SERVO_PRTT -> pr_servo_remove_tt()

   TT_SERVO_DM && pr_servo -> tt_servo_dm() 
   TT_SERVO_SA -> tt_servo_sa()