In most example project for embedded system there is a system file in which we can find structures for different peripheral as well as the memory mapping of the peripheral register, in addition there is also a module per peripheral that contains basic function to manipulate the periheral like: periph_enable, periph_write, periph_read; this is the architecture i have in mind when i tackle a new project.
Actually i started to work with a BF609 but now with an embedded linux in it, my task consist in writing a communication driver with another device via UART, as usual i tried to look for the files i used to use but in vain, i can't find the mapping of the different peripheral.
I started to read this book, i undrestand that the kernel see each device like a file and that a driver is mainly the implementation of the open, close, read and writefunctions in these file but i still don't undrestand how these functions communicate with peripheral registers.
My questions:
1) How device drivers recognise the mapping of the peripheral is there sth i missed, is there any example that explain how to implement simple read and write functions via UART for example
2) Where can i find the mapping of the peripheral in the buildroot directory
Thanks in advance
Related
I'm trying to read and write data off i2c in slave mode and have found several examples to do this in userspace including this most relevant one from NXP (I'm using the iMX8MQ):
https://source.codeaurora.org/external/imx/imx-test/tree/test/mxc_i2c_slave_test/mxc_i2c_slave_test.c?h=imx_4.14.78_1.0.0_ga
However, it looks like if I want to read data, it would be a polling based implementation because it looks like i2c-dev does not provide a way to register userspace callbacks when i2c data is available. Not even sure if any Linux device drivers allow doing this at all. Am I correct in assuming that there is no non-blocking and asynchronous way of doing an i2c read from userspace in slave mode?
I'm not very familiar with writing device drivers so even if I wanted to implement my own, similar to this one:
https://github.com/torvalds/linux/blob/master/drivers/i2c/i2c-slave-eeprom.c
is it a good idea to call a userspace function when data became available (for instance when the driver received an I2C_SLAVE_STOP)?
(iMX6 SOC running Linux 3.0)
I need to run a few I2C transactions in my board_init function. I tried calling i2c_get_adapter, then i2c_transfer, those being available in kernel mode, but i2c_get_adapter returns NULL. It's already called imx6q_add_imx_i2c, which is a wrapper around platform_device_register_full, but that isn't enough.
I can manipulate GPIO in board_init by calling gpio_request to obtain access, and gpio_free at the end. Is there something analogous to those functions for i2c?
--- added details ---
I've got a LAN9500A USB 100Base-T Ethernet MAC connected to a LAN9303 3-port switch with a virtual PHY. The MAC has a GPIO reset line that has to be turned off before it will spring to life and enumerate on the USB. That's done in board_init because it's completely nonstandard, so we don't want to patch the stock driver to manipulate some GPIO that's not part of the device.
The problem I'm having is that even though the MAC is permanently attached to the VPHY, it's not noticing it's connected, and an "ip link show eth1" command shows NO-CARRIER. I found I can kickstart it by unmasking the VPHY's Device Ready interrupt via I2C, but I also have to mask it immediately, or I get infinite interrupts. That's not the right solution, but Microchip has been no help in showing me a better way. But we don't want to patch the MAC driver with code to fiddle with the PHY.
There is no PHY driver for this part, and the MII interface to the VPHY doesn't include any interrupt-related registers, so it must be done through I2C. Writing a PHY driver just to flip a bit on and off once seems a lot of trouble, especially for a newbie like me who's never written a driver before.
I can do it in Python in a startup script, but that, too, seems like a heavyweight solution to a lightweight problem.
That's a wrong approach. Board file supposed to register device drivers and pass important information to them, rather than act as a device driver itself. I'm not sure if what you're trying to do is even possible.
If you really need to extract something from your I2C device on a very early stage - do that in the bootloader and pass the data to kernel via cmdline (U-boot, by the way, has I2C support for a quite some time). Then later, kernel might do appropriate actions depending on what you have passed to it.
I have booted a ubuntu on a ZedBoard. I want to transfer data between fpga and linux. For example, I want to write or read a register from linux. What is best way for doing it? I have not any idea.
Thanx.
First of all, you need to specifically say what you want to do, for example. if you want to access the IO signals on the FPGA, you need to first add the GPIO module to your system, synthesize and implement it.
Then you use the Linux GPIO Driver to access the port as it is explained in this page:
Linux GPIO Driver
The GPIO driver fits in the Linux GPIO framework which is not a char
mode driver. Yet it does provide access to the GPIO by user space
through the sysfs filesystem. This allows each GPIO signal to be read
and written in similar manner to a char mode device. The interface is
somewhat documented in the kernel tree at Documentation/gpio.txt. The
following text is aimed to augment, not replace the existing
documentation.
For other, more complex interfaces you need to create your own driver or use one of the drivers that are available and modify it to fit your needs.
I have been trying to understand the mfd framework in linux kernel to write my drivers but there seems to be hardly any documentation and the mfd core itself doesnt seem to have much helpful comments. So, I am trying to understand what the mfd_cell structure describes. That seems to be the basis here. What I m particularly interested in finding out is if this used as a general abstraction for 'x' number of sub-devices or is it intended/useful for a full hierarchy of sub-devices.
An MFD is a device that contains several sub-devices. For instance, in embedded systems a PMIC usually contains a battery manager, a charger and sometimes devices with unrelated functions like a USB PHY, an Audio codec, a Real-Time Clock, ...
A cell is meant to describe a sub-device. The mfd subsystem will use the information registered in that structure to create a platform device for each sub-device, along with the platform_data for the sub-device.
You can specify more advanced things like the resources used by this device and suspend-resume operations (to be called from the driver for the sub-device).
The new platform devices that are created will have the cell structure as their platform data and can access the real platform data through cell->platform_data.
I am a linux newbie, trying to understand Linux Device Model. I had been going through Linux 3.1.6 code base, particularly the driver part and found that
some of the drivers were using (for example i2c-bus device : linux-3.1.6/drivers/i2c/i2c-dev.c) *register_chrdev()* and
few others (for example pci bus : linux-3.1.6/drivers/pci/bus.c) were using *device_register()*.
My question is when to use register_chrdev (yes, I know its for a character device, but why not use device_register) and device_register ?
Does that depend on where does the driver developer wants his device/driver to be listed down, like devfs vs sysfs ? Or the interface exposed to the user space to access the device ?
One function registers a character device association (hooking up major:minors to your function), the other just creates an abstract device object (only), so to speak. The two are complementary. The device object is used for the generation of an event so that udev can, if there is also a cdev association registered, create a node in /dev. (Compare with, for example, drivers/char/misc.c.)
See when you register a device as a character device specifically then following thing happens:
Major Number is given in accordance. If you use any device depending on functionality whose registration is based on character device (like tty, input etc), then those will have their respective major number. Thats why its said that dont assign major number statically if not sure.
And
There are certain file operations which correspond to operations that could be performed on char devices only.
Do ask if any query.