config.txt (Raspberry Pi) (Rev #5, changes)

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Introduction

The Raspberry Pi boot loader uses the config.txt file to hold configuration parameters relevant at boot time. It is a plain text file, resident in the DOS partition of the boot SD card, alongside bootcode.bin, start.elf and fixup.dat (for more information on these other files, see Software information: Raspberry Pi: Firmware).

It should not be confused with cmdline.txt (which is used to pass parameters to RISC OS at boot time).

Entries required by RISC OS

The following lines are present in the standard config.txt for RISC OS. Note that each parameter appears on a separate line of the file.

fake_vsync_isr=1
framebuffer_swap=0
gpu_mem=64
init_emmc_clock=100000000
ramfsfile=CMOS
ramfsaddr=0x508000
kernel=RISCOS.IMG

These entries have the following meanings:

• fake_vsync_isr=1
  Triggers an SMI interrupt at vertical sync (VSYNC) pulse

• framebuffer_swap=0
  Corrects a problem where red and blue colour channels are swapped on later firmware.

• gpu_mem=64
  Allocates 64MB RAM to the GPU. At present this enumerates the default setting.

• init_emmc_clock=100000000
  Sets the eMMC clock rate to 100MHz. At present this enumerates the default setting.

• ramfsfile=CMOS
  Name of CMOS RAM file to be loaded

• ramfsaddr=0x508000
  Address to load the CMOS RAM. This address is 5MiB after the kernel start address (0×8000) so the RISC OS ROM cannot exceed 5MiB in size.

• kernel=RISCOS.IMG
  Filename of the RISC OS ROM

Optional sound entries

The following two entries are useful if you want to use the 3.5mm audio output jack instead of via the HDMI cable.

• hdmi_ignore_edid_audio=1
  Force the audio to use the stereo audio jack output.

• audio_pwm_mode=2
  Improves the sound quality and reduces annoying hissing.

Optional video entries

• hdmi_blanking=1
  Add this line if you want the monitor to switch to standby when the DPMS screen saver activates. Without this line, the screen will go blank but the monitor will stay “on”.

• hdmi_force_hotplug=1
  Forces video output to use the HDMI connector. Use this if the Pi is having difficulties detecting your HDMI display.

• disable_overscan
  Don’t want those black borders at the edge of the screen? Try adding disable_overscan=1 to get rid of them.

• max_framebuffer_width, max_framebuffer_height, hdmi_pixel_freq_limit
  These parameters are used to specify the maximum screen size. The largest screen size officially supported by the Raspberry Pi is 1920×1200, but it should be possible to increase this to 2560×1440, as explained in the “Display support” section of this page, and there are reports of people squeezing 3840×2160 from a Pi 3.

Optional miscellaneous entries

The following entries may also be useful in certain circumstances:

• boot_delay
  Number of seconds to wait before loading the kernel. Use this if your SD card needs a while to get ready.

• bootcode_delay
  Number of seconds to wait before loading start.elf. Use this if your monitor takes a long time to start up (e.g. if a low-resolution desktop appears on cold boot, but restarting the Pi gives you a 1920×1080 desktop).

External links

• The documentation pages on the Raspberry Pi website contain further information on the parameters mentioned above, and many more besides.
  • Analogue audio options
  • Boot options
  • Video options

• RPIconfig at elinux.org