Working on original Pi model B with Adafruit 2.8 inch resistive screen

[xunker]

Just a note that I have got your tool working on my original (2011.12) Pi Model B. Thank you for putting all the effort in to making it work!

Test System

• Original (2011.12) Pi Model B (512MB)
• Adafruit 2.8" 320x240 TFT w/ Touch screen for Raspberry Pi
• Raspbian Buster, kernel 5.10.103
• xfce window manager

Video Modes

Here are the video modes I've tested, along with the applicable lines from /boot/config.txt.

512x342 (for Mac Plus/Mini vMac), 10 fps

gpu_mem=32 # optional, just to free up memory
hdmi_cvt=512 342 10 1 0 0 0 # [width] [height] [framerate] [aspect] [margins] [interlace] [rb]
hdmi_group=2
hdmi_mode=87

640x480, 10 fps

gpu_mem=32 # optional, just to free up memory
hdmi_cvt=640 480 10 1 0 0 0 # [width] [height] [framerate] [aspect] [margins] [interlace] [rb]
hdmi_group=2
hdmi_mode=87

800x600

hdmi_group=2
hdmi_mode=9

1024x768

hdmi_group=2
hdmi_mode=16

Build options

Here are the options I used:

# DMA
cmake -DSPI_BUS_CLOCK_DIVISOR=6 -DADAFRUIT_ILI9341_PITFT=ON \
      -DBACKLIGHT_CONTROL=OFF -DSINGLE_CORE_BOARD=ON \
      -DARMV6Z=ON -DSTATISTICS=0 \
      -DUSE_DMA_TRANSFERS=ON -DDMA_RX_CHANNEL=4

# Non-DMA
cmake -DSPI_BUS_CLOCK_DIVISOR=6 -DADAFRUIT_ILI9341_PITFT=ON \
      -DBACKLIGHT_CONTROL=OFF -DSINGLE_CORE_BOARD=ON \
      -DARMV6Z=ON -DSTATISTICS=0 -DUSE_DMA_TRANSFERS=OFF

On my machine, the the default RX DMA channel was used, and 4 was the next channel that worked.

I haven't tried backlight control yet, that the reason for -DBACKLIGHT_CONTROL=OFF.

Installation Notes

I used the systemd install instructions, but needed to do a couple of things extra:

• symlink "/etc/systemd/system/fbcp-ili9341.service" in to "/etc/systemd/system/multi-user.target.wants"
  • cd /etc/systemd/system/multi-user.target.wants; sudo ln -s /etc/systemd/system/fbcp-ili9341.service
• install the executable in the system path
  • sudo install -m 0755 -t /usr/local/sbin fbcp-ili9341

After those two extra steps, fbcp started up properly on boot.

CPU Usage

I watched the CPU usage in 640x480@10fps for one minute with an static screen. Here is the CPU usage I recorded:

• With DMA: 1.3-2.9% cpu usage
• Without DMA: 3.6-5.9% cpu usage

Even without DMA, the CPU usage is 1/3rd of Notro/fbtft with the same resolution and fps! Nice work!