Re: [Discuss-gnuradio] Debug IO pins

[Eric Blossom]

On Sat, Aug 19, 2006 at 11:14:33PM -0700, Oussama Sekkat wrote:
> Hi,
> I generated a signal using the usrp_siggen.py function and tried to use the
> IO_pins on the basic TX board to monitor the digital output on a logic
> analyzer but it seems that no signal goes to those pins.
> Is there somehting I need to change in the verilog code to be able to use
> the debug IO pins?
> Any suggestions on how to observe the output on a logic analyzer?
> 
> Thank you,
> Oussama.

Hi Oussama,

There are two ways to control the i/o pins.  Either from the host, or
from within the FPGA.

To control them from the host no changes are required in the verilog.
>From python you need to tell it to "output enable" the pins you are
interested, and then write whatever values you like to them:

>From gr-usrp/src/usrp1.i:

  /*!
   * \brief Write direction register (output enables) for pins that go to 
daughterboard.
   *
   * \param which_dboard        [0,1] which d'board
   * \param value               value to write into register
   * \param mask                which bits of value to write into reg
   *
   * Each d'board has 16-bits of general purpose i/o.
   * Setting the bit makes it an output from the FPGA to the d'board.
   *
   * This register is initialized based on a value stored in the
   * d'board EEPROM.  In general, you shouldn't be using this routine
   * without a very good reason.  Using this method incorrectly will
   * kill your USRP motherboard and/or daughterboard.
   */
  bool _write_oe (int which_dboard, int value, int mask);

  /*!
   * \brief Write daughterboard i/o pin value
   *
   * \param which_dboard        [0,1] which d'board
   * \param value               value to write into register
   * \param mask                which bits of value to write into reg
   */
  bool write_io (int which_dboard, int value, int mask);

  /*!
   * \brief Read daughterboard i/o pin value
   *
   * \param which_dboard        [0,1] which d'board
   * \returns register value if successful, else READ_FAILED
   */
  int read_io (int which_dboard);


E.g.,

  # Assumes Basic_Tx in slot A.
  # Do not do this blindly!  Output enabing all the i/o pins
  # on other daughterboards will cause problems (burn up daughterboard
  # and/or FPGA)

  u = usrp.sink_c(0, 64)

  side = 0  # side A
  u._write_oe(side, 0xffff, 0xffff)     # set all i/o pins as outputs
  counter = 0
  while 1:
    u.write_io(side, counter, 0xffff)
    counter = (counter + 1) & 0xffff


If however, you're trying to control the debug pins from the FPGA
you'll need to output enable them from the host, and enable them as
debug outputs.  You do the last step by writing to the FR_DEBUG_ENABLE
FPGA register:

>From usrp/firmware/include/fpga_regs_common.h:

// If the corresponding bit is set, internal FPGA debug circuitry
// controls the i/o pins for the associated bank of daughterboard
// i/o pins.  Typically used for debugging FPGA designs.

#define FR_DEBUG_EN             14
#  define bmFR_DEBUG_EN_TX_A           (1 << 0)        // debug controls TX_A 
i/o
#  define bmFR_DEBUG_EN_RX_A           (1 << 1)        // debug controls RX_A 
i/o
#  define bmFR_DEBUG_EN_TX_B           (1 << 2)        // debug controls TX_B 
i/o
#  define bmFR_DEBUG_EN_RX_B           (1 << 3)        // debug controls RX_B 
i/o

These defines are available in python like this:

from usrp_fpga_regs import *

  u = usrp.sink_c(0, 64)
  u._write_oe(0, 0xffff, 0xffff)
  u._write_fpga_reg(FR_DEBUG_EN, bmFR_DEBUG_EN_TX_A)


Eric