4.15 HDMI

本例程演示通过linux的libdrm库提供的接口来访问内核DRM显示框架，实现HDMI接口屏的显示。

测试硬件环境：

  • MYD-C437X-EVM 开发板一块

  • HDMI连接线一根，HDMI接口的显示器一台

  • USB转TTL调试串口一根，连接MYD-C437X-EVM J16和PC, PC端波特率设置115200-8-n-1

测试软件环境：

  • Linux Kernel 4.1.18

  • modetest应用程序

测试过程：

  • 编译modetest应用程序，进入到Buildroot所在目录，执行make menuconfig进入如所示的配置界面

选中Install test programs 保存配置退出。

 /home/qinlh/builtroot/myir-buildroot/.config - Buildroot 2017.02-git-g92c215a C
o> Target packages > Libraries > Graphics > libdrm ----------------------------
  +-------------------------------- libdrm ---------------------------------+
  |  Arrow keys navigate the menu.  <Enter> selects submenus ---> (or empty |  
  |  submenus ----).  Highlighted letters are hotkeys.  Pressing <Y>        |  
  |  selectes a feature, while <N> will exclude a feature.  Press           |  
  |  <Esc><Esc> to exit, <?> for Help, </> for Search.  Legend: [*] feature |  
  | +---------------------------------------------------------------------+ |  
  | |    --- libdrm                                                       | |  
  | |    [ ]   radeon                                                     | |  
  | |    [ ]   amdgpu                                                     | |  
  | |    [ ]   nouveau                                                    | |  
  | |    -*-   omap (experimental)                                        | |  
  | |    [ ]   etnaviv (experimental)                                     | |  
  | |    [ ]   exynos (experimental)                                      | |  
  | |    [ ]   freedreno                                                  | |  
  | |    [ ]   tegra (experimental)                                       | |  
  | |    [ ]   vc4                                                        | |  
  | |    [*]   Install test programs                                      | |  
  | +---------------------------------------------------------------------+ |  
  +-------------------------------------------------------------------------+  
  |        <Select>    < Exit >    < Help >    < Save >    < Load >         |  
  +-------------------------------------------------------------------------+

执行make命令等待一段时间，编译好的modetest应用程序位于<WORKDIR>/Filesystem/myir-buildroot/output/build/libdrm-2.4.74/tests/modetest/modetest

  • 修改启动要加载的设备树为myd_c437x_evm_hdmi.dtb：

SD卡启动：编辑位于SD中的uEnv_ramdisk.txt的内容，编辑完成后将文件名改为uEnv.txt。内容改为如下所示：

# This uEnv.txt file can contain additional environment settings that you
# want to set in U-Boot at boot time.  This can be simple variables such
# as the serverip or custom variables.  The format of this file is:
#    variable=value
# NOTE: This file will be evaluated after the bootcmd is run and the
#       bootcmd must be set to load this file if it exists (this is the
#       default on all newer U-Boot images.  This also means that some
#       variables such as bootdelay cannot be changed by this file since
#       it is not evaluated until the bootcmd is run.
#optargs=video=HDMI-A-1:800x600

# Uncomment the following line to enable HDMI display and disable LCD display.
#fdtfile=myd_c437x_evm.dtb
fdtfile=myd_c437x_evm_hdmi.dtb
devtype=mmc
devnum=0
bootdir=/
bootpart=0:1
uenvcmd=if run loadimage; then run loadfdt; run loadramdisk; echo Booting from mmc${mmcdev} ...; run ramargs; print bootargs; bootz ${loadaddr} ${rdaddr} ${fdtaddr}; fi

EMMC启动和NFS启动：uboot启动阶段进入控制台，设置环境变量

MYIR># setenv fdtfile myd_c437x_evm_hdmi.dtb
MYIR># saveenv
Saving Environment to FAT...
Card did not respond to voltage select!
** Bad device mmc 0 **
MYIR># reset

  • 上述启动方式的设备树文件修改完毕后，上电进入到开发板，将之前编译好的modetest应用程序拷贝到开发板的/usr/bin目录下

  • 把HDMI连接线一端插入到开发板的J9 (HDMI)接口，另一端接入到显示器的HDMI接口，执行应用程序：

# modetest -s 25@27:1024x768
trying to open device 'i915'...failed
trying to open device 'amdgpu'...failed
trying to open device 'radeon'...failed
trying to open device 'nouveau'...failed
trying to open device 'vmwgfx'...failed
trying to open device 'omapdrm'...done
setting mode 1024x768-60Hz@XR24 on connectors 25, crtc 27

显示屏上即可看到画面。

  • MYIR AM437X系列其它板型HDMI测试可以参照本例程进行。