Data Sheet

ManualsBrands4D Systems ManualsRaspberry Pi Accessories / HATs3.2" Primary Display for Raspberry Pi A+/B+/2

4D SYSTEMS 4DPi-32-II Primary Display – Raspberry Pi Compatible

4DPi

-32

-II Primary Display

– Raspberry

4.5. Change the SPI Freq and Compression

The 4DPi-32-II can be adjusted to work with a range

of SPI Frequencies and levels of compression,

depending on the requirements of the end

product/project.

Increasing the frequency can result in a higher

Frame Rate (FPS), however will use more power

and processor time.

Increasing the level of the compression can also

result in a higher FPS, but may cause the display to

corrupt.

By default, a SPI Frequency of 48Mhz is used, with

a Compression level of 7.

The following parameters are the defaults in the

/boot/cmdline.txt file, and can be edited to adjust

the Frequency and Compression level.

4dpi.sclk=48000000

4dpi.compress=7

Setting compress to be 1 will enable the kernel to

control the level of compression based on the

frequency selected. This however is not guaranteed

to have a good end result, and may require

manually setting the compression level if

corruption on the display is experienced.

If corruption or display anomalies occur at any

given compression level, try to lower it by 1 value

and check if this has improved.

Note, changing the frequency and compression

require a restart of the Raspberry Pi.

4.6. Backlight Control

The backlight is controllable in two possible ways.

One is using simple on/off control, which is done by

sending a GPIO command to the on-board

processor, which then turns the backlight on and

off. The other is using a DMA -PWM output from

the Raspberry PI and controlling the backlight

brightness.

The control of the backlight is selected using the

Jumper J1, selecting ON/OFF or DMA control. For

the simple ON/OFF control GPIO18 is used.

The backlight brightness can be controlled from

the terminal, or from a bash script.

Controlling the backlight using ON/OFF control

requires root access.

$ sudo su

Executing the following command will control the

backlight:

To turn the backlight OFF:

# echo 0 > /sys/class/backlight/4d-

hats/brightness

To turn the backlight ON:

# echo 1 > /sys/class/backlight/4d-

hats/brightness

To control the backlight using DMA-PWM, ensure

that the Jumper J1 is on PWM.

The following command can be used to set the

backlight from 0 to 100%.

# echo 80 > /sys/class/backlight/32-hat-

pwm/brightness

The above will set the backlight to 80%. Simply

change the ‘echo 80’ to be anything from 0 to 100.

4.7. Parameters Listing

The following is a list of all the custom parameters

used by the 4DPi-32-II.

rotate: Screen rotation 0/90/180/270 (int)

compress: SPI compression 0/1/2/3/4/5/6/7 (int)

sclk: SPI clock frequency (long)

Valid SPI Frequency values (4dpi.sclk):

Values can be almost anything. This has been tested

up to 64Mhz. Common values would include

64000000 (64MHz), 48000000 (Default), 32000000,

24000000 etc.

Valid Compression values (4dpi.compress):

0 (compression off)

1 (compression on, auto set based on sclk value)

2 (lowest), 3, 4, 5, 6, 7 (highest compression)

These parameters can be set or read from the

/boot/cmdline.txt file, and they can be read from

the /sys/modules/4dpi/parameters directory.

For example:

$ cat /sys/modules/4dpi/parameters/rotate

Will display the current rotation saved.