spi interface lcd module free sample

LCD, or Liquid Crystal Displays, are great choices for many applications. They aren’t that power-hungry, they are available in monochrome or full-color models, and they are available in all shapes and sizes.

Waveshare actually has several round LCD modules, I chose the 1.28-inch model as it was readily available on Amazon. You could probably perform the same experiments using a different module, although you may require a different driver.

Another difference is simply with the labeling on the display. There are two pins, one labeled SDA and the other labeled SCL. At a glance, you would assume that this is an I2C device, but it isn’t, it’s SPI just like the Waveshare device.

Open the Arduino folder. Inside you’ll find quite a few folders, one for each display size that Waveshare supports. As I’m using the 1.28-inch model, I selected theLCD_1inch28folder.

Once you do that, you can open your Arduino IDE and then navigate to that folder. Inside the folder, there is a sketch file namedLCD_1inch28.inowhich you will want to open.

The error just seems to be with a couple of the Chinese characters used in the comments of the sketch. You can just ignore the error, the sketch will compile correctly in spite of it.

Unfortunately, Waveshare doesn’t offer documentation for this, but you can gather quite a bit of information by reading theLCD_Driver.cppfile, where the functions are somewhat documented.

Here is the hookup for the ESP32 and the GC9A01 display.  As with most ESP32 hookup diagrams, it is important to use the correct GPIO numbers instead of physical pins. The diagram shows the WROVER, so if you are using a different module you’ll need to consult its documentation to ensure that you hook it up properly.

The TFT_eSPI library is ideal for this, and several other, displays. You can install it through your Arduino IDE Library Manager, just search for “TFT_eSPI”.

The Animated Eyes sketch can be found within the sample files for the TFT_eSPI library, under the “generic” folder.  Assuming that you have wired up the second GC9A01 display, you’ll want to use theAnimated_Eyes_2sketch.

The GC9A01 LCD module is a 1.28-inch round display that is useful for instrumentation and other similar projects. Today we will learn how to use this display with an Arduino Uno and an ESP32.

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The parallel interface typically controls the LCD via 8 data pins and 3 control lines. The control lines used are Enable (E), Register Select (RS), and Read/Write (R/W). RS tells the LCD module if the information being sent is an Instruction or Data. The Enable tells the LCD module that the data or instruction in the register is ready to be interpreted by the LCD Module. Some controllers may have more than one Enable Control Line. The Read/Write tells the module whether to write data or read data from the register.

Serial LCD controllers typically have one Serial Data Line that writes data and cannot read. Normally, a Register Select Line(Sometimes designated A0) is used to tell the controller whether the incoming data is display information or a controller command

SPI, or Serial Peripheral Interface bus, is a synchronous (data is synchronized to the clock) serial data link standard that operates in full duplex mode, which means that devices that can communicate with one another simultaneously. To do this, two data lines are required. With this standard, devices communicate in a master/slave mode, where the master device (host processor) initiates the data and the clock. The LCD module is the (or one of the) peripheral slave device(s) attached to the data bus. Multiple peripherals (display modules and other devices) are addressed on the same serial data bus. However, the LCD module will only listen to the data it sees when the Chip Select line is active (usually low). If the Chip Select line is inactive (usually High), the LCD module listens to the data on the bus, but ignores it. The SDO line is not active when this state occurs. The SPI bus is comprised of four logic signals, two control lines and two data lines and is commonly referred to as SPI (4 wire).

Occasionally, SDI (serial data in) may be called out as MOSI (Master Out Slave In) from Motorola"s original name for these lines and MISO (Master In Slave Out) for SDO. The chip select line may be alternatively labeled SS (Slave-Select), or STE (Slave Transmit Enable). SPI is sometimes referred to as National Semiconductor"s trademark Microwire, which is essentially a predecessor of SPI, which only supports half duplex.

With CS (Chip-Select) the corresponding peripheral device is selected by the LCD Controller. This pin is mostly active-low. In the unselected state the SDO lines are hi-impedance and therefore inactive. The clock line SCL is brought to the device whether it is selected or not. The clock serves as synchronization of the data communication.

The chip select signal CS is optional for a single device system, because you could tie the CS input at the LCD Module low, if the other lines are dedicated to SPI use. This is sometimes called a 3 Wire SPI Interface.

SPI Data transmissions usually involve two shift registers. Most display module applications normally use 8-bit words. However, different size words, such as 12 bit, are also used. By convention, the most significant bit is shifted out of one shift register while the least significant bit is shifted in. The word is then written into memory if the CS (chip-select) is low (active). If not, the data is ignored.

Since the SPI interface protocol is a de facto standard, many variations of the standard protocol are used. For instance, chip manufacturers may use some of the parallel data lines when configuring the IC driver chip for serial communication. chip manufacturers may use some of the parallel data lines when configuring the IC driver chip for serial communication.

I2C uses only two bi-directional lines, Serial Data Line (SDA) and Serial Clock (SCL), which are both typically pulled up with resistors. Typical voltages used are +5 V or +3.3 V. One of the strengths of the I2C interface is that a micro can control multiple devices with just the two I/O pins and software. Because of the I2C design, it is only half-duplex. The interface generally transmits 8-bit words, sending the most significant bit first.

Connector ports for devices such like cameras, displays, basebands, and RF interfaces are standardized under MIPI Alliance specifications. These specifications include design, manufacturing costs, structural complexity, power consumption and degree of EMI.

SPI stands for Serial Peripheral Interface. SPI is a simple serial bus that is often used by LCD or OLED controllers. SPI as implemented for OLED and LCD controllers typically uses a “3-wire SPI” or “4-wire SPI” scheme.

SPI is not addressed, so each slave must have its own SS line. For example, in order for one master to talk to 6 slaves, the master will need 1 input (MISO) and 8 outputs (MOSI, SCK, and the 6 slave selects).

Traditionally, we are urged to think of SPI as a 16-bit shift register, with 8 bits in the master, and 8 bits in the slave. The master loads its message destined for the slave, the slave loads its data for the master, the master gives 8 clocks, and the data shifts simultaneously from the master to the slave (over MOSI) and from the slave to the master (over MISO).

A SPI master can be implemented by GPIO under software control, or it may be implemented in hardware. SPI slaves are almost always implemented in hardware.

Now you should have been expecting the fourth line to be MISO, so you could read data back from the display–but with LCD controllers, there is a twist.

We need some history to understand the 4th line as used in SPI displays. Traditionally, parallel interface LCD controllers had two registers, a Command register and a Data register. You would write the command to the Command register, then write the appropriate data to the Data register. To select between them, there was a C/D (or A0) line. Set the line to 1=Command or 0=Data then the write the 8 bits of data.

Now back to “4-wire SPI,” the 4th wire is “C/D.” So you can either make an 8-bit SPI write to the display controller’s Command register or an 8-bit SPI write its Data register depending on the state of the C/D line.

There are some controllers that use the “3-wire SPI” transfer format (encoding C/D and R/W as additional bits in the SPI transfer), but also have a MISO pin that can be used for reading data back from the display. So these displays use 4 physical wires, but have the a data encoding similar to the “3-wire SPI”.

Initially “3-wire SPI” seems like a better solution, less wires, same function, what is there not to like? Well, the same history that gave us the extra C/D line now gives us an extra C/D bit–instead of using 8-bit transfers “3-wire SPI” uses 9-bit (!) transfers.

If you are using software and GPIO to implement the SPI master, then it is no problem to modify the code to make it transfer 9 bits at a time. However, making 9-bit transfer with SPI hardware implementations may be difficult or impossible. Some of the newer and more innovative processors have more flexible hardware SPI implementations that may allow 9-bit transfers.

There is another non-SPI-standard thing that some SPI display controllers do, and that is they use their single data line bidirectionallly–for both writing and reading. Typically you would write the “read command” bits, then make the data line an input, then read back some number of bits from the display. Some controllers go a bit (sorry) further and encode the traditional Read/Write line from the old parallel interface into a 10th R/W bit. These use a 10-bit SPI transfer, with a bi-directional data line.

Each LCD/OLED controller IC that supports SPI will include its specific SPI transfer format, and list the formats for its read and write commands. You will want to look at the format of the controller’s SPI interface and evaluate whether you can use the hardware SPI Master that is part of your microcontroller, or if you need to write your own software SPI master.

The purpose of this guide is to get your 0.96″ color LCD display successfully operating with your Arduino, so you can move forward and experiment and explore further types of operation with the display. This includes installing the Arduino library, making a succesful board connection and running a demonstration sketch.

The display uses the SPI data bus for communication, and is a 3.3V board. You can use it with an Arduino or other 5V board as the logic is tolerant of higher voltages.

The ST7789 TFT module contains a display controller with the same name: ST7789. It’s a color display that uses SPI interface protocol and requires 3, 4 or 5 control pins, it’s low cost and easy to use. This display is an IPS display, it comes in different sizes (1.3″, 1.54″ …) but all of them should have the same resolution of 240×240 pixel, this means it has 57600 pixels. This module works with 3.3V only and it doesn’t support 5V (not 5V tolerant).

The ST7789 display module shown in project circuit diagram has 7 pins: (from right to left): GND (ground), VCC, SCL (serial clock), SDA (serial data), RES (reset), DC (or D/C: data/command) and BLK (back light).

As mentioned above, the ST7789 TFT display controller works with 3.3V only (power supply and control lines). The display module is supplied with 3.3V (between VCC and GND) which comes from the Arduino board.

To connect the Arduino to the display module, I used voltage divider for each line which means there are 4 voltage dividers. Each voltage divider consists of 2.2k and 3.3k resistors, this drops the 5V into 3V which is sufficient.

In these videos, the SPI (GPIO) bus is referred to being the bottleneck. SPI based displays update over a serial data bus, transmitting one bit per clock cycle on the bus. A 320x240x16bpp display hence requires a SPI bus clock rate of 73.728MHz to achieve a full 60fps refresh frequency. Not many SPI LCD controllers can communicate this fast in practice, but are constrained to e.g. a 16-50MHz SPI bus clock speed, capping the maximum update rate significantly. Can we do anything about this?

Given that the SPI bus can be so constrained on bandwidth, how come fbcp-ili9341 seems to be able to update at up to 60fps? The way this is achieved is by what could be called adaptive display stream updates. Instead of uploading each pixel at each display refresh cycle, only the actually changed pixels on screen are submitted to the display. This is doable because the ILI9341 controller, as many other popular controllers, have communication interface functions that allow specifying partial screen updates, down to subrectangles or even individual pixel levels. This allows beating the bandwidth limit: for example in Quake, even though it is a fast pacing game, on average only about 46% of all pixels on screen change each rendered frame. Some parts, such as the UI stay practically constant across multiple frames.

A hybrid of both Polled Mode SPI and DMA based transfers are utilized. Long sequential transfer bursts are performed using DMA, and when DMA would have too much latency, Polled Mode SPI is applied instead.

Undocumented BCM2835 features are used to squeeze out maximum bandwidth: SPI CDIV is driven at even numbers (and not just powers of two), and the SPI DLEN register is forced in non-DMA mode to avoid an idle 9th clock cycle for each transferred byte.

Good old interlacing is added into the mix: if the amount of pixels that needs updating is detected to be too much that the SPI bus cannot handle it, the driver adaptively resorts to doing an interlaced update, uploading even and odd scanlines at subsequent frames. Once the number of pending pixels to write returns to manageable amounts, progressive updating is resumed. This effectively doubles the maximum display update rate. (If you do not like the visual appearance that interlacing causes, it is easy to disable this by uncommenting the line #define NO_INTERLACING in file config.h)

The result is that the SPI bus can be kept close to 100% saturation, ~94-97% usual, to maximize the utilization rate of the bus, while only transmitting practically the minimum number of bytes needed to describe each new frame.

This program neither utilizes the default SPI driver, so a line such as dtparam=spi=on in /boot/config.txt should also be removed so that it will not cause conflicts.

-DPIRATE_AUDIO_ST7789_HAT=ON: If specified, targets a Pirate Audio 240x240, 1.3inch IPS LCD display HAT for Raspberry Pi with ST7789 display controller

-DKEDEI_V63_MPI3501=ON: If specified, targets a KeDei 3.5 inch SPI TFTLCD 480*320 16bit/18bit version 6.3 2018/4/9 display with MPI3501 display controller.

-DGPIO_TFT_DATA_CONTROL=number: Specifies/overrides which GPIO pin to use for the Data/Control (DC) line on the 4-wire SPI communication. This pin number is specified in BCM pin numbers. If you have a 3-wire SPI display that does not have a Data/Control line, set this value to -1, i.e. -DGPIO_TFT_DATA_CONTROL=-1 to tell fbcp-ili9341 to target 3-wire ("9-bit") SPI communication.

fbcp-ili9341 always uses the hardware SPI0 port, so the MISO, MOSI, CLK and CE0 pins are always the same and cannot be changed. The MISO pin is actually not used (at the moment at least), so you can just skip connecting that one. If your display is a rogue one that ignores the chip enable line, you can omit connecting that as well, or might also be able to get away by connecting that to ground if you are hard pressed to simplify wiring (depending on the display).

-DSPI_BUS_CLOCK_DIVISOR=even_number: Sets the clock divisor number which along with the Pi core_freq= option in /boot/config.txt specifies the overall speed that the display SPI communication bus is driven at. SPI_frequency = core_freq/divisor. SPI_BUS_CLOCK_DIVISOR must be an even number. Default Pi 3B and Zero W core_freq is 400MHz, and generally a value -DSPI_BUS_CLOCK_DIVISOR=6 seems to be the best that a ILI9341 display can do. Try a larger value if the display shows corrupt output, or a smaller value to get higher bandwidth. See ili9341.h and waveshare35b.h for data points on tuning the maximum SPI performance. Safe initial value could be something like -DSPI_BUS_CLOCK_DIVISOR=30.

-DSINGLE_CORE_BOARD=ON: Pass this option if you are running on a Pi that has only one hardware thread (Pi Model A, Pi Model B, Compute Module 1, Pi Zero/Zero W). If not present, autodetected.

-DDISPLAY_CROPPED_INSTEAD_OF_SCALING=ON: If set, and source video frame is larger than the SPI display video resolution, the source video is presented on the SPI display by cropping out parts of it in all directions, instead of scaling to fit.

-DDISPLAY_BREAK_ASPECT_RATIO_WHEN_SCALING=ON: When scaling source video to SPI display, scaling is performed by default following aspect ratio, adding letterboxes/pillarboxes as needed. If this is set, the stretching is performed breaking aspect ratio.

If the above does not work, try specifying -DSPI_BUS_CLOCK_DIVISOR=8 or =10 to make the display run a little slower, or try with -DUSE_DMA_TRANSFERS=OFF to troubleshoot if DMA might be the issue. If you are using another display controller than ILI9341, using a much higher value, like 30 or 40 may be needed. When changing CMake options, you can reissue the CMake directive line without having to reclone or recreate the build directory. However you may need to manually delete file CMakeCache.txt between changing options to avoid CMake remembering old settings.

If the size of the default HDMI output /dev/fb0 framebuffer differs from the resolution of the display, the source video size will by default be rescaled to fit to the size of the SPI display. fbcp-ili9341 will manage setting up this rescaling if needed, and it will be done by the GPU, so performance should not be impacted too much. However if the resolutions do not match, small text will probably appear illegible. The resizing will be done in aspect ratio preserving manner, so if the aspect ratios do not match, either horizontal or vertical black borders will appear on the display. If you do not use the HDMI output at all, it is probably best to configure the HDMI output to match the SPI display size so that rescaling will not be needed. This can be done by setting the following lines in /boot/config.txt:

These lines hint native applications about the default display mode, and let them render to the native resolution of the TFT display. This can however prevent the use of the HDMI connector, if the HDMI connected display does not support such a small resolution. As a compromise, if both HDMI and SPI displays want to be used at the same time, some other compatible resolution such as 640x480 can be used. See Raspberry Pi HDMI documentation for the available options to do this.

The refresh speed of the display is dictated by the clock speed of the SPI bus that the display is connected to. Due to the way the BCM2835 chip on Raspberry Pi works, there does not exist a simple speed=xxx Mhz option that could be set to define the bus speed. Instead, the SPI bus speed is derived from two separate parameters: the core frequency of the BCM2835 SoC in general (core_freq in /boot/config.txt), and the SPI peripheral CDIV (Clock DIVider) setting. Together, the resulting SPI bus speed is then calculated with the formula SPI_speed=core_freq/CDIV.

Adjust the CDIV value by passing the directive -DSPI_BUS_CLOCK_DIVISOR=number in CMake command line. Possible values are even numbers 2, 4, 6, 8, .... Note that since CDIV appears in the denominator in the formula for SPI_speed, smaller values result in higher bus speeds, whereas higher values make the display go slower. Initially when you don"t know how fast your display can run, try starting with a safe high setting, such as -DSPI_BUS_CLOCK_DIVISOR=30, and work your way to smaller numbers to find the maximum speed the display can cope with. See the table at the end of the README for specific observed maximum bus speeds for different displays.

Ensure turbo speed. This is critical for good frame rates. On the Raspberry Pi 3 Model B, the BCM2835 core runs by default at 400MHz (resulting in 400/CDIV MHz SPI speed) if there is enough power provided to the Pi, and if the CPU temperature does not exceed thermal limits. If the CPU is idle, or voltage is low, the BCM2835 core will instead revert to non-turbo 250MHz state, resulting in 250/CDIV MHz SPI speed. This effect of turbo speed on performance is significant, since 400MHz vs non-turbo 250MHz comes out to +60% of more bandwidth. Getting 60fps in Quake, Sonic or Tyrian often requires this turbo frequency, but e.g. NES and C64 emulated games can often reach 60fps even with the stock 250MHz. If for some reason under-voltage protection is kicking in even when enough power should be fed, you can force-enable turbo when low voltage is present by setting the value avoid_warnings=2 in the file /boot/config.txt.

Perhaps a bit counterintuitively, underclock the core. Setting a smaller core frequency than the default turbo 400MHz can enable using a smaller clock divider to get a higher resulting SPI bus speed. For example, if with default core_freq=400 SPI CDIV=8 works (resulting in SPI bus speed 400MHz/8=50MHz), but CDIV=6 does not (400MHz/6=66.67MHz was too much), you can try lowering core_freq=360 and set CDIV=6 to get an effective SPI bus speed of 360MHz/6=60MHz, a middle ground between the two that might perhaps work. Balancing core_freq= and CDIV options allows one to find the maximum SPI bus speed up to the last few kHz that the display controller can tolerate. One can also try the opposite direction and overclock, but that does then of course have all the issues that come along when overclocking. Underclocking does have the drawback that it makes the Pi run slower overall, so this is certainly a tradeoff.

The main option to control CPU usage vs performance aspect is the option #define ALL_TASKS_SHOULD_DMA in config.h. Enabling this option will greatly reduce CPU usage. If this option is disabled, SPI bus utilization is maximized but CPU usage can be up to 80%-120%. When this option is enabled, CPU usage is generally up to around 15%-30%. Maximal CPU usage occurs when watching a video, or playing a fast moving game. If nothing is changing on the screen, CPU consumption of the driver should go down very close to 0-5%. By default #define ALL_TASKS_SHOULD_DMA is enabled for Pi Zero, but disabled for Pi 3B.

The CMake option -DUSE_DMA_TRANSFERS=ON should always be enabled for good low CPU usage. If DMA transfers are disabled, the driver will run in Polled SPI mode, which generally utilizes a full dedicated single core of CPU time. If DMA transfers are causing issues, try adjusting the DMA send and receive channels to use for SPI communication with -DDMA_TX_CHANNEL= and -DDMA_RX_CHANNEL= CMake options.

If your SPI display bus is able to run really fast in comparison to the size of the display and the amount of content changing on the screen, you can try enabling #define UPDATE_FRAMES_IN_SINGLE_RECTANGULAR_DIFF option in config.h to reduce CPU usage at the expense of increasing the number of bytes sent over the bus. This has been observed to have a big effect on Pi Zero, so is worth checking out especially there.

If the SPI display bus is able to run really really really fast (or you don"t care about frame rate, but just about low CPU usage), you can try enabling #define UPDATE_FRAMES_WITHOUT_DIFFING option in config.h to forgo the adaptive delta diffing option altogether. This will revert to naive full frame updates for absolutely minimum overall CPU usage.

Interestingly, fbcp-ili9341 is about ~33msecs faster than a cheap 3.5" KeDei HDMI display. I do not know if this is a result of the KeDei HDMI display specifically introducing extra latency, or if all HDMI displays connected to the Pi would have similar latency overhead. An interesting question is also how SPI would compare with DPI connected displays on the Pi.

Unfortunately a limitation of SPI connected displays is that the VSYNC line signal is not available on the display controllers when they are running in SPI mode, so it is not possible to do vsync locked updates even if the SPI bus bandwidth on the display was fast enough. For example, the 4 ILI9341 displays I have can all be run faster than 75MHz so SPI bus bandwidth-wise all of them would be able to update a full frame in less than a vsync interval, but it is not possible to synchronize the updates to vsync since the display controllers do not report it. (If you do know of a display that does actually expose a vsync clock signal even in SPI mode, you can try implementing support to locking on to it)

Having no vsync is not all bad though, since with the lack of vsync, SPI displays have the opportunity to obtain smoother animation on content that is not updating at 60Hz. It is possible that content on the SPI display will stutter even less than what DPI or HDMI displays on the Pi can currently provide (although I have not been able to test this in detail, except for the KeDei case above).

If USE_GPU_VSYNC is disabled, then a busy spinning GPU frame snapshotting thread is used to drive the updates. This will produce smoother animation in content that does not maintain a fixed 60Hz rate. Especially in OpenTyrian, a game that renders at a fixed 36fps and has slowly scrolling scenery, the stuttering caused by USE_GPU_VSYNC is particularly visible. Running on Pi 3B without USE_GPU_VSYNC enabled produces visually smoother looking scrolling on an Adafruit 2.8" ILI9341 PiTFT set to update at 119Hz, compared to enabling USE_GPU_VSYNC on the same setup. Without USE_GPU_VSYNC, the dedicated frame polling loop thread "finds" the 36Hz update rate of the game, and then pushes pixels to the display at this exact rate. This works nicely since SPI displays disregard vsync - the result is that frames are pushed out to the SPI display immediately as they become available, instead of pulling them at a fixed 60Hz rate like HDMI does.

The codebase captures screen framebuffers by snapshotting via the VideoCore vc_dispmanx_snapshot() API, and the obtained pixels are then routed on to the SPI-based display. This kind of polling is performed, since there does not exist an event-based mechanism to get new frames from the GPU as they are produced. The result is inefficient and can easily cause stuttering, since different applications produce frames at different paces. Ideally the code would ask the VideoCore API to receive finished frames in callback notifications immediately after they are rendered, but this kind of functionality does not exist in the current GPU driver stack. In the absence of such event delivery mechanism, the code has to resort to polling snapshots of the display framebuffer using carefully timed heuristics to balance between keeping latency and stuttering low, while not causing excessive power consumption. These heuristics keep continuously guessing the update rate of the animation on screen, and they have been tuned to ensure that CPU usage goes down to 0% when there is no detected activity on screen, but it is certainly not perfect. This GPU limitation is discussed at raspberrypi/userland#440. If you"d like to see fbcp-ili9341 operation reduce latency, stuttering and power consumption, please throw a (kind!) comment or a thumbs up emoji in that bug thread to share that you care about this, and perhaps Raspberry Pi engineers might pick the improvement up on the development roadmap. If this issue is resolved, all of the #define USE_GPU_VSYNC, #define SAVE_BATTERY_BY_PREDICTING_FRAME_ARRIVAL_TIMES and #define SELF_SYNCHRONIZE_TO_GPU_VSYNC_PRODUCED_NEW_FRAMES hacks from the previous section could be deleted from the driver, hopefully leading to a best of all worlds scenario without drawbacks.

The speed of the SPI bus is linked to the BCM2835 core frequency. This frequency is at 250MHz by default (on e.g. Pi Zero, 3B and 3B+), and under CPU load, the core turbos up to 400MHz. This turboing directly scales up the SPI bus speed by 400/250=+60% as well. Therefore when choosing the SPI CDIV value to use, one has to pick one that works for both idle and turbo clock speeds. Conversely, the BCM core reverts to non-turbo speed when there is only light CPU load active, and this slows down the display, so if an application is graphically intensive but light on CPU, the SPI display bus does not get a chance to run at maximum speeds. A way to work around this is to force the BCM core to always stay in its turbo state with force_turbo=1 option in /boot/config.txt, but this has an unfortunate effect of causing the ARM CPU to always run in turbo speed as well, consuming excessive amounts of power. At the time of writing, there does not yet exist a good solution to have both power saving and good performance. This limitation is being discussed in more detail at raspberrypi/firmware#992.

By default fbcp-ili9341 builds with a statistics overlay enabled. See the video fbcp-ili9341 ported to ILI9486 WaveShare 3.5" (B) SpotPear 320x480 SPI display to find details on what each field means. Build with CMake option -DSTATISTICS=0 to disable displaying the statistics. You can also try building with CMake option -DSTATISTICS=2 to show a more detailed frame delivery timings histogram view, see screenshot and video above.

The fbcp part in the name means framebuffer copy; specifically for the ILI9341 controller. fbcp-ili9341 is not actually a framebuffer copying driver, it does not create a secondary framebuffer that it would copy bytes across to from the primary framebuffer. It is also no longer a driver only for the ILI9341 controller. A more appropriate name might be userland-raspi-spi-display-driver or something like that, but the original name stuck.

Edit the file config.h and comment out the line #define DISPLAY_OUTPUT_LANDSCAPE. This will make the display output in portrait mode, effectively rotating it by 90 degrees. Note that this only affects the pixel memory reading mode of the display. It is not possible to change the panel scan order to run between landscape and portrait, the SPI displays typically always scan in portrait mode. The result is that it will change the panel vsync tearing mode from "straight line tearing" over to "diagonal tearing" (see the section About Tearing above).

Enable the option #define DISPLAY_ROTATE_180_DEGREES in config.h. This should rotate the SPI display to show up the other way around, while keeping the HDMI connected display orientation unchanged. Another option is to utilize a /boot/config.txt option display_rotate=2, which rotates both the SPI output and the HDMI output.

I don"t know, I don"t currently have any to test. Perhaps the code does need some model specific configuration, or perhaps it might work out of the box. I only have Pi 3B, Pi 3B+, Pi Zero W and a Pi 3 Compute Module based systems to experiment on. Pi 2 B has been reported to work by users (#17).

If the display controller is one of the currently tested ones (see the list above), and it is wired up to run using 4-line SPI, then it should work. Pay attention to configure the Data/Control GPIO pin number correctly, and also specify the Reset GPIO pin number if the device has one.

If fbcp-ili9341 does not support your display controller, you will have to write support for it. fbcp-ili9341 does not have a "generic SPI TFT driver routine" that might work across multiple devices, but needs specific code for each. If you have the spec sheet available, you can ask for advice, but please do not request to add support to a display controller "blind", that is not possible.

Perhaps. This is a more recent experimental feature that may not be as stable, and there are some limitations, but 3-wire ("9-bit") SPI display support is now available. If you have a 3-wire SPI display, i.e. one that does not have a Data/Control (DC) GPIO pin to connect, configure it via CMake with directive -DGPIO_TFT_DATA_CONTROL=-1 to tell fbcp-ili9341 that it should be driving the display with 3-wire protocol.

This has only been tested on my Adafruit SSD1351 128x96 RGB OLED display, which can be soldered to operate in 3-wire SPI mode, so testing has not been particularly extensive.

Yes, fbcp-ili9341 shows the output of the HDMI display on the SPI screen, and both can be attached at the same time. A HDMI display does not have to be connected however, although fbcp-ili9341 operation will still be affected by whatever HDMI display mode is configured. Check out tvservice -s on the command line to check what the current DispmanX HDMI output mode is.

At the moment fbcp-ili9341 has been developed to only display the contents of the main DispmanX GPU framebuffer over to the SPI display. That is, the SPI display will show the same picture as the HDMI output does. There is no technical restriction that requires this though, so if you know C/C++ well, it should be a manageable project to turn fbcp-ili9341 to operate as an offscreen display library to show a completely separate (non-GPU-accelerated) image than what the main HDMI display outputs. For example you could have two different outputs, e.g. a HUD overlay, a dashboard for network statistics, weather, temps, etc. showing on the SPI while having the main Raspberry Pi desktop on the HDMI.

make sure the display is configured to run 4-wire SPI mode, and not in parallel mode or 3-wire SPI mode. You may need to solder or desolder some connections or set a jumper to configure the specific driving mode. Support for 3-wire SPI displays does exist, but it is more limited and a bit experimental.

This suggests that the power line or the backlight line might not be properly connected. Or if the backlight connects to a GPIO pin on the Pi (and not a voltage pin), then it may be that the pin is not in correct state for the backlight to turn on. Most of the LCD TFT displays I have immediately light up their backlight when they receive power. The Tontec one has a backlight GPIO pin that boots up high but must be pulled low to activate the backlight. OLED displays on the other hand seem to stay all black even after they do get power, while waiting for their initialization to be performed, so for OLEDs it may be normal for nothing to show up on the screen immediately after boot.

fbcp-ili9341 runs a clear screen command at low speed as first thing after init, so if that goes through, it is a good sign. Try increasing -DSPI_BUS_CLOCK_DIVISOR= CMake option to a higher number to see if the display driving rate was too fast. Or try disabling DMA with -DUSE_DMA_TRANSFERS=OFF to see if this might be a DMA conflict.

This suggests same as above, increase SPI bus divisor or troubleshoot disabling DMA. If DMA is detected to be the culprit, try changing up the DMA channels. Double check that /boot/config.txt does not have any dtoverlays regarding other SPI display drivers or touch screen controllers, and that it does NOT have a dtparam=spi=on line in it - fbcp-ili9341 does not use the Linux kernel SPI driver.

Double check the Data/Command (D/C) GPIO pin physically, and in CMake command line. Whenever fbcp-ili9341 refers to pin numbers, they are always specified in BCM pin numbers. Try setting a higher -DSPI_BUS_CLOCK_DIVISOR= value to CMake. Make sure no other fbcp programs or SPI drivers or dtoverlays are enabled.

If the colors looks off in some other fashion, it is possible that the display is just being driven at a too high SPI bus speed, in which case try making the display run slower by choosing a higher -DSPI_BUS_CLOCK_DIVISOR= option to CMake. Especially on ILI9486 displays it has been observed that the colors on the display can become distorted if the display is run too fast beyond its maximum capability.

First, make sure the display is a 4-wire SPI and not a 3-wire one. A display is 4-wire SPI if it has a Data/Control (DC) GPIO line that needs connecting. Sometimes the D/C pin is labeled RS (Register Select). Support for 3-wire SPI displays does exist, but it is experimental and not nearly as well tested as 4-wire displays.

In this list, Rated SPI Bus Speed is the maximum clock speed that the display controller is rated to run at. The Obtained Bus Speed column lists the fastest SPI bus speed that was achieved in practice, and the core_freq BCM Core speed and SPI Clock Divider CDIV setting that was used to achieve that rate. Note how most display controllers can generally be driven much faster than what they are officially rated at in their spec sheets.

All the ILI9341 displays work nice and super fast at ~70-80MHz. My WaveShare 3.5" 320x480 ILI9486 display runs really slow compared to its pixel resolution, ~32MHz only. See fbcp-ili9341 ported to ILI9486 WaveShare 3.5" (B) SpotPear 320x480 SPI display for a video of this display in action. Adafruit"s 320x480 3.5" HX8357D PiTFTs is ~64% faster in comparison.

Search around, or ask the manufacturer of the display what the maximum SPI bus speed is for the device. This is the most important aspect to getting good frame rates, but unfortunately most web links never state the SPI speed rating, or they state it ridiculously low like in the spec sheets. Try and buy to see, or ask in some community forums from people who already have a particular display to find out what SPI bus speed it can achieve.

One might think that since Pi Zero is slower than a Pi 3, the SPI bus speed might not matter as much when running on a Pi Zero, but the effect is rather the opposite. To get good framerates on a Pi Zero, it should be paired with a display with as high SPI bus speed capability as possible. This is because the higher the SPI bus speed is, the more autonomously a DMA controller can drive it without CPU intervention. For the same reason, the interlacing technique does not (currently at least) perform well on a Pi Zero, so it is disabled there by default. ILI9341s run well on Pi Zero, ILI9486 on the other hand is quite difficult to combine with a Pi Zero.

Ultimately, it should be noted that parallel displays (DPI) are the proper method for getting fast framerates easily. SPI displays should only be preferred if display form factor is important and a desired product might only exist as SPI and not as DPI, or the number of GPIO pins that are available on the Pi is scarce that sacrificing dozens of pins to RGB data is not feasible.

Displays are generally manufactured to utilize one specific interfacing method, with the exception that some displays have a both I²C and SPI modes that can be configured via soldering.

Tomáš Suk, Cyril Höschl IV, and Jan Flusser, Rectangular Decomposition of Binary Images., a useful research paper about merging monochrome bitmap images to rectangles, which gave good ideas for optimizing SPI span merges across multiple scan lines,

If you would like to help push Raspberry Pi SPI display support further, there are always more things to do in the project. Here is a list of ideas and TODOs for recognized work items to contribute, roughly rated in order of increasing difficulty.

Vote up issue raspberrypi/userland/#440 if you would like to see Raspberry Pi Foundation improve CPU performance and reduce latency of the Pi when used with SPI displays.

Vote up issue raspberrypi/firmware/#992 if you would like to see Raspberry Pi SPI bus to have high throughput even when the Pi CPU is not under heavy CPU load (better SPI throughput with lower power consumption), a performance feature only SDHOST on the Pi currently enjoys.

If you have access to a high frequency scope/logic analyzer (~128MHz), audit the utilization of the SPI MOSI bus to find any remaining idle times on the bus, and analyze their sources.

Implement a kernel module that enables userland programs to allocate DMA channels, which fbcp-ili9341 could use to amicably reserve its own DMA channels without danger of conflicting.

Improve support for 3-wire displays, e.g. for 1) "17-bit" 3-wire communication, 2) fix up SPI_3WIRE_PROTOCOL + ALL_TASKS_SHOULD_DMA to work together, or 3) fix up SPI_3WIRE_PROTOCOL + OFFLOAD_PIXEL_COPY_TO_DMA_CPP to work together.

Port the high performance DMA-based SPI communication technique from fbcp-ili9341 over to another project that uses the SPI bus for something else, for close to 100% saturation of the SPI bus in the project.

If you are knowledgeable with BCM2835 DMA, investigate whether the hacky dance where two DMA channels need to be used to reset and resume DMA SPI transfers when chaining, can be avoided?

If you have contacts with Broadcom, ask them to promote use of the SoC hardware with DMA chaining + mixed SPI & non-SPI tasks as a first class tested use case. Current DMA SPI hardware behavior of BCM2835 is, to say the least, surprising.