Currently, I am developing my Own Video Frame Buffer Driver with help of Linux PCIe and Virtual Frame Buffer Driver.
My Custom Driver works fine on 720X480P Video Resolution but getting some slow on 720P Video Resolution.
I have just directly mapped frame buffer memory with DDR2 Memory coming with PCIe Interface on FPGA System.
DMA Controller Stuffs are implemented in FPGA System.
How can I develop DMA Read/Write Operation in my own frame buffer driver to solve my slow frame rate issue?
Please let me know if anyone has idea about this.
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I am studying Operating Systems, and came across divice controllers.
I gathered that a device controller is hardware whereas a device driver is software.
I also know that a HDD and a SSD both have a small PCB buit into them and I assume those PCB's are the device controllers.
Now what I want to know is if there is another device controller on the PC/motherboard side of the bus/cable connecting the HDD/SSD to the OS?
Is the configuration: OS >> Device Driver >> Bus >> Device Controller >> HDD/SSD
Or is it: OS >> Device Driver >> Device Controler >> Bus >> Device Controller >> HDD/SSD
Or is it some other configuration?
Sites I visited for answers:
Tutorialspoint
JavaPoint
Idc online
Quora
Most hard-disks on desktop are SATA or NVME. eMMC is popular for smartphones but some might use something else. These are hardware interface standards that describe the way to interact electrically with those disks. It tells you what voltage at what frequency and for what amount of time you need to apply (a signal) to a certain pin (a bus line) to make the device behave or react in a certain way.
Most computers are separated in a few external chips. On desktop, it is mostly SATA, NVME, DRAM, USB, Audio Output, network card and graphics card. Even though there is few chips, the CPU would be very expensive if it had to support all those hardware interface standards on the same silicon chip. Instead, the CPU implements PCI/PCI-e as a general interface to interact with all those chips using memory mapped registers. Each of these devices have an external PCI-e controller between the device and the CPU. In the same order as above, you have AHCI, NVME controller, DRAM (not PCI and in the CPU), xHCI (almost everywhere) and Intel HDA (example). Network cards are PCI-e and there isn't really a controller outside the card. Graphics card are also self standing PCI-e devices.
So, the OS detects the registers of those devices that are mapped in the address space. The OS writes at those locations, and it will write the registers of the devices. PCI-e devices can read/write DRAM directly but this is managed by the CPU in its general implementation of the PCI-e standard most likely by doing some bus arbitration. The CPU really doesn't care what's the device that it is writing. It knows that there is a PCI register there and the OS instructs to write it with something so it does. It just happens that this device is an implementation of a standard and that the OS developers read the standard so they write the proper values in those registers and the proper data structures in DRAM to make sure that the device knows what to do.
Drivers implement the standard of the software interface of those controllers. The drivers are the ones instructing the CPU on values to write and writing the proper data structures in DRAM for giving commands to the controllers. The user thread simply places the syscall number in a conventionnal register determined by the OS developers and they call an instruction to jump into the kernel at a specific address that the kernel decides by writing a register at boot. Once there, the kernel looks at the register for the number and determines what driver to call based on the operation.
On Linux and some place else, it is done with files. You call syscalls on files and the OS has a driver attached to the file. They are called virtual files. A lot of transfer mechanisms are similar to the reading/writing files pattern so Linux uses that to make a general driver model where the kernel doesn't even need to understand the driver. The driver just says create me a file there that's not really on the hard disk and if someone opens it and calls an operation on it then call this function that's there in my driver. From there, the driver can do whatever it wants because it is in kernel mode. It just creates the proper data structures in DRAM and writes the registers of the device it drives to make it do something.
I have little background on how these hardware actually works, but now I'm required to learn how to write a Linux frame buffer driver for Android devices.
I'm confused by Linux graphics stack. From what I understand, on a desktop computer the compositing window manager interacts with DRM, which then sends data to specific video card driver. On the other hand there are some kind of controllers retrieving data from GPU's memory through DMA and send it to the monitor, as suggested by the answer here .
Also by diagram at page 29 of this book, I figured that a frame buffer driver is on top of actual graphic devices, so it must need to interact with specific video card driver, for example, an nVidia driver.
But when I google writing a frame buffer driver for an embedded device, the results show that as if the driver is directly responsible for contacting with the LCD, so it looks like it's even below a video card driver.
So is a frame buffer driver actually a video card driver?
A framebuffer driver provides an interface for
Modesetting
Memory access to the video buffer
Basic 2D acceleration operations (e.g. for scrolling)
To provide this interface, the framebuffer driver generally talks to the hardware directly.
For example, the vesafb framebuffer driver will use the VESA standard interface to talk to the video hardware. However, this standard is limited, so there isn't really much hardware acceleration going on and drawing is slow.
Another example is the intelfb framebuffer driver. It talks to some intel hardware using a proprietary interface, that exposes more acceleration facilities, so it is faster.
Nowadays, KMS drivers are used instead for most hardware. They do both expose a framebuffer and also access to other GPU functionality, e.g. OpenGL, through DRM.
Your confusion seems to arise from the fact, that the framebuffer driver and the X11 GPU driver are in fact competing! This is why, if you have a KMS system, the switch between graphical and text consoles is instant, however, with a non-KMS system, it is slow, as both the fb driver and the X11 driver need to re-initialize the video hardware on console switch.
Find more information in the comprehensive talk Linux Graphics Demystified by Martin Fiedler:
http://keyj.emphy.de/files/linuxgraphics_en.pdf
I am trying to use DMA to program an FPGA connected to an OMAP-L138's SPI bus, but without success.
Currently, I am using the stock davinci-spi driver (drivers/spi/spi-davinci.c)that comes with linux 3.19. FPGA configuration is successful (without DMA enabled), but it is very slow. I am using a device tree to configure the SPI interface.
I would like to use DMA to improve performance, however from looking at the spi-davinci.c source code and its device tree bindings, the driver does not appear to support DMA when configured with device tree. Is my understanding correct? If so, are there any plans to support DMA transfers using davinci's SPI driver when also using device tree?
Here are a few guidelines to achieve your goal:
First, check if the SPI has it's own DMA engine. If it doesn't, perhaps there's a generic DMA controller on board. You can check this by looking at the SPI datasheet and looking at the board interconnect schematics.
If none of the above are true, then you can't use DMA with the SPI.
If the SPI has its own DMA, you'll need to write a driver for that.
If there's a DMA on board, it's probably utilized by other components, search for dma_dngine driver for that particular device. Then you'll need to create a DMA client for that particular DMA engine.
Please read:
DMA Provider
DMA Client
Good luck
I am writing a device driver on Xillinux that will read and write data to an FPGA application over Xillybus.
Basically I want to create device nodes such as /dev/pe1, and when I write to the nodes my device driver will form packets of data and then write the packets into the xillybus nodes eg. /dev/xillybus_write_32
Is it possible to simply open an existing /dev node inside a kernel module, and then perform I/O operations on it? Or is it better to just write a userspace driver?
After reading LDD3 and some other articles on kernel development, I've decided to abandon the idea of writing my custom device driver and put the logic in runtime instead. Thanks for the advice goldilocks.
I need to transfer video data to and from an FPGA device over PCI in a linux environment. I'm using a third party PCI master core on the FPGA. So far, I've implemented a simple DMA controller on the FPGA to transfer data from the FPGA to the CPU, using consecutive PCI write bursts.
Next, I need to transfer video data from the CPU to the FPGA. What is the best way to go about this?
Should I implement a module on the FPGA which performs a whole bunch of burst reads over PCI. Or is there a way to get the CPU to efficiently write data into the FPGA's memory using PCI write bursts?
My bandwidth requirements are around 30 MB/s in both directions.
Thanks.
You could do posted writes from CPU like what video card drivers do but you'll need to have some driver magic such as setting MTRR (which means you might have some architectural dependency). If you want to be safe DMA read from FPGA is a better way to go. 30MB/s isn't much.
Sounds to me the FPGA should master both reads and writes. Otherwise you would hog the host CPU. That's a classic task for a DMA (and you cannot guarantee a DMA exists on every host).