DMCC

Open issues:

• status bits always 0
• power can't be read (always 0)
• PID w/ integral term doesn't track, especially velocity
• position PID always at full power, needs option to limit

Wiring:

Battery, dual MicroFit connector in center:

• 2x Top : GND
• 2x Bot : V_Bat (closest to board)

The top and bottom pairs are electrically joined, and do not go to specific motors. The extra wires are there simply to create a higher effective gauge.

Polou Connector (Power + QEI):

(ref: http://www.pololu.com/product/2275)

  Re: Motor power
  Bk: Motor GND
  Gr: Encoder GND
  Bu: Encoder Vcc (3.3V - 20V)
  Ye: Encoder Out A
  Wh: Encoder Out B

DMCC QEI (left to right from BB-P8 to P9):

  QEI1-1 (Re)  5V
  QEI1-2 (Gr)  QEI1_A?
  QEI1-3 (Bk)  GND
  QEI1-4 (Ye)  QEI1_B?

  QEI2-1 (Re)  5V
  QEI2-2 (Gr)  QEI2_A?
  QEI2-3 (Bk)  GND
  QEI2-4 (Ye)  QEI2_B?

Wire reassignment when connecting from DMCC to Pololu encoders (which are also reordered from stock):

  (Wh/Ye tape side)     (encoder wire colors, not the physical order)
    Re  5V         -->        Bl
    Ye  QEI        -->  QEI_B Wh
    Gr  QEI        -->  QEI_A Ye
    Bk  GND        -->        Gr
  (non-tape side)

PIC controller

Each motor can be in 1 of 4 modes:

• 00 - power (static power setting)
• 01 - PID position
• 10 - PID velocity
• 11 - Fault

I2C

All capes are on the BBB I2C2 bus (P19,P20), which is i2c-1 on linux

  Cape EEPROMs map 1-to-1 to DMCC address:
    Cape EEprom   DMCC I2c    DMCC Board  DMCC Switch
    1-0x54        1-0x2c        0
    1-0x55        1-0x2d        1         1-ON 2-OFF
    1-0x56        1-0x2e        2
    1-0x57        1-0x2f        3

EEPROMs show up as UU since they are registered with a kernel device driver DMCC PIC chip is not registered, so shows up by number as an unbound device

root@arm:~# i2cdetect -y -r 1

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
     00:          -- -- -- -- -- -- -- -- -- -- -- -- --
     10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
     20: -- -- -- -- -- -- -- -- -- -- -- -- -- 2d -- --
     30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
     40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
     50: -- -- -- -- UU UU UU UU -- -- -- -- -- -- -- --
     60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
     70: -- -- -- -- -- -- -- --

EEPROM dump:

# od -c /sys/bus/i2c/devices/1-0055/eeprom
0000000 252   U   3 356   A   0   D   M   C   C       (   D   u   a   l
0000020       M   o   t   o   r       C   o   n   t   r   o   l       C
0000040   a   p   e   )  \0  \0   M   k   0   6   E   x   a   d   l   e
0000060   r   .   c   o   m  \0  \0  \0  \0  \0   D   M   C   C       M
0000100   k   .   0   6  \0  \0  \0  \0  \0  \0  \0  \0   0   0   0   2
0000120   9  \n  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0

WARNING: All reads are single bytes (8-bits). Executing 16-bit reads will cause the DMCC to lock up the i2c bus and require power cycle

Commands:

  i2cget -y 1 0x2[cdef] <register addy>
  i2cdump -y -r 0x00-0xef 1 0x2[cdef]

Testing based on Exadler protocol document:

 Motor status: ??

      0x00  R   Status     Always returns 0x00 ??
      0x01  R?  Polarity   Always returns 0x00 ??

  Power values:
      [-10000,10000] (two's compliment)
      Settings take effect only after writing to 0xff (see 0xff for values)

      0x02  RW  M1 Power low bit
      0x03  RW  M1 Power high bit
      0x04  RW  M2 Power low bit
      0x05  RW  M2 Power high bit

  QEIs: 32-bit, only correct after refresh

      0x10  R   QEI1 Pos low bit
      0x11
      0x12
      0x13  R   QEI1 Pos high bit

      0x14  R   QEI2 Pos low bit
      0x15
      0x16
      0x17  R   QEI2 Pos high bit

      0x18  R   QEI1 Vel low bit
      0x19  R   QEI1 Vel high bit

  Targets:
      0x20
      0x2b

  PID Error:
      0x2e  ???
      0x2f

  PID values
      Docs say these values are *256 for the sake of integer calcs, but it seems
      that is completely internal to the PIC firmware

      0x30  RW  M1 Pos Kp low bit
      ...
      0x4b  RW  M2 Vel Kd high bit

  Cape version "DMCC Mk.06"
      0xe0
      ..
      0xef

Refresh: i2cset -y 1 0x2d 0xff 0x00

Exadler Python interface:

  import DMCC    # DMCC.so should be in path

  # dmcc_id:[0,3], motor_id:[1,2]

  # sets motor power: [-10000,10000]
  #   motor indicator light will be green when +, red when -
  DMCC.setMotor(dmcc_id, motor_id, powe0x2dcr)

  # Battery voltage in volts
  DMCC.getMotorVoltage(dmcc_id)

  # Battery voltage in millivolts (integer)
  DMCC.getMotorVoltageInt(dmcc_id)

  # returns QEI position (at least [-1M, +1M], probably 32-bit)
  DMCC.getQEI(dmcc_id,motor_id)

  # returns QEI velocity [-X,+X]
  DMCC.getQEIVel(dmcc_id,motor_id)

  # PID values are [-32768,32767]
  # pos_or_vel: Pos = 0 , Vel = 1
  #
  # NB: each mode (pos/vel) has its own set of PID constants
  #
  # Example constants from sample program: -5248 -75 -500  (for position, seem reasonable)
  # If velocity doesn't reach target, increase I to eliminate SSE
  #    (-20000,-30000, 000) almost track but has massive overshoot, especially when slowing
  #     can't track vel=0 with such a high I
  DMCC.setPIDConstants(dmcc_id, motor_id, pos_or_vel, kp, ki, kd)

  # these need PID set before they work
  DMCC.setTargetPos(1,1,position)
  DMCC.setTargetVel(1,1,velocity)

MISC NOTES

Control theory notes SSE of P controller: error = Input/(1+Kp)

Test motor's max vel: ~ [-275,280]

Convert signed hex: unpack('h',pack('H',0xec78)) # MSB to LSB

Decode hex: '444d4343204d6b2e3036'.decode('hex')