If your HDMI TV or monitor is too sensitive and doesn't display correctly, it is worth to adjust the HDMI PHY on the XU3/XU4.\\
To use this feature, the Kernel version must be be 3.10.82-47 or higher.

**This is a portion of the default boot.ini file comes with the 3.10.82-47 update.**
<code>
#------------------------------------------------------------------------------
#
# HDMI-PHY Parameter Control
#
#------------------------------------------------------------------------------
#------------------------------------------------------------------------------
#
#  TMDS data amplitude control.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to 20 mVdiff amplitude level.
#  tx_amp_lvl : 0 = 760 mVdiff(Min), 31 = 1380 mVdiff(Max)
#
#  Hardkernel default hdmi_tx_amp_lvl = 31(1380 mVdiff);
#------------------------------------------------------------------------------
setenv hdmi_tx_amp_lvl  "31"

#------------------------------------------------------------------------------
#
#  TMDS data amplitude fine control for each channel.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to 20 mVdiff amplitude level.
#  tx_lvl : 0 = 0 mVdiff(Min), 3 = 60 mVdiff(Max)
#
#  Hardkernel default
#      hdmi_tx_lvl_ch0 = 3, hdmi_tx_lvl_ch1 = 3, hdmi_tx_lvl_ch2 = 3,
#------------------------------------------------------------------------------
setenv hdmi_tx_lvl_ch0      "3"
setenv hdmi_tx_lvl_ch1      "3"
setenv hdmi_tx_lvl_ch2      "3"

#------------------------------------------------------------------------------
#
#  TMDS data pre-emphasis level control.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to -0.45dB emphasis level except for 1
#  tx_emp_lvl : 0 = 0 db(Min), 1 = -0.25 db, 2 = 0.7 db, 15 = -7.45 db(Max)
#
#  Hardkernel default hdmi_tx_emp_lvl = 6 (-2.50 db);
#------------------------------------------------------------------------------
setenv hdmi_tx_emp_lvl      "6"

#------------------------------------------------------------------------------
#
#  TMDS clock amplitude control.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to 20 mVdiff amplitude level.
#  clk_amp_lvl : 0 = 790 mVdiff(Min), 31 = 1410 mVdiff(Max)
#
#  Hardkernel default hdmi_clk_amp_lvl = 31 (1410 mVdiff)
#------------------------------------------------------------------------------
setenv hdmi_clk_amp_lvl     "31"

#------------------------------------------------------------------------------
#
#  TMDS data source termination resistor control.
#
#------------------------------------------------------------------------------
#
#  tx_res :
#      0 = Source Termination OFF(Min), 1 = 200 ohm, 2 = 300 ohm, 3 = 120 ohm(Max)
#
#  Hardkernrel default hdmi_tx_res = 0 (Source Termination OFF)
#------------------------------------------------------------------------------
setenv hdmi_tx_res      "0"
</code>


**If you have a display compatibility issue by HDMI signal strength, try this parameters.**
<code>
#------------------------------------------------------------------------------
#
# HDMI-PHY Parameter Control
#
#------------------------------------------------------------------------------
#------------------------------------------------------------------------------
#
#  TMDS data amplitude control.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to 20 mVdiff amplitude level.
#  tx_amp_lvl : 0 = 760 mVdiff(Min), 31 = 1380 mVdiff(Max)
#
#  Hardkernel default hdmi_tx_amp_lvl = 31(1380 mVdiff);
#------------------------------------------------------------------------------
# trial hdmi_tx_amp_lvl = 13(1020 mVdiff);
setenv hdmi_tx_amp_lvl  "13"

#------------------------------------------------------------------------------
#
#  TMDS data amplitude fine control for each channel.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to 20 mVdiff amplitude level.
#  tx_lvl : 0 = 0 mVdiff(Min), 3 = 60 mVdiff(Max)
#
#  Hardkernel default
#      hdmi_tx_lvl_ch0 = 3, hdmi_tx_lvl_ch1 = 3, hdmi_tx_lvl_ch2 = 3,
#------------------------------------------------------------------------------
setenv hdmi_tx_lvl_ch0      "0"
setenv hdmi_tx_lvl_ch1      "0"
setenv hdmi_tx_lvl_ch2      "0"
#or try below parameters
#setenv hdmi_tx_lvl_ch0      "1"
#setenv hdmi_tx_lvl_ch1      "1"
#setenv hdmi_tx_lvl_ch2      "1"


#------------------------------------------------------------------------------
#
#  TMDS data pre-emphasis level control.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to -0.45dB emphasis level except for 1
#  tx_emp_lvl : 0 = 0 db(Min), 1 = -0.25 db, 2 = 0.7 db, 15 = -7.45 db(Max)
#
#  Hardkernel default hdmi_tx_emp_lvl = 6 (-2.50 db);
#------------------------------------------------------------------------------
setenv hdmi_tx_emp_lvl      "6"

#------------------------------------------------------------------------------
#
#  TMDS clock amplitude control.
#
#------------------------------------------------------------------------------
#
#  1LSB corresponds to 20 mVdiff amplitude level.
#  clk_amp_lvl : 0 = 790 mVdiff(Min), 31 = 1410 mVdiff(Max)
#
#  Hardkernel default hdmi_clk_amp_lvl = 31 (1410 mVdiff)
#------------------------------------------------------------------------------
# hdmi_clk_amp_lvl = 16 (1110 mVdiff)
setenv hdmi_clk_amp_lvl     "16"

#------------------------------------------------------------------------------
#
#  TMDS data source termination resistor control.
#
#------------------------------------------------------------------------------
#
#  tx_res :
#      0 = Source Termination OFF(Min), 1 = 200 ohm, 2 = 300 ohm, 3 = 120 ohm(Max)
#
#  Hardkernrel default hdmi_tx_res = 0 (Source Termination OFF)
#------------------------------------------------------------------------------
# 200ohm termination
setenv hdmi_tx_res      "1"
#------------------------------------------------------------------------------
</code>