I have written a simple character driver.Now I want to write a UART driver for a omap 4460
processor.
In what way I should start ie how should I relate it with the character driver?
I dont know where to start.I have gone through the manual of the processor and know the functionality of the driver.Please provide me some steps
Related
I have a task to write a serial driver for uart and tty_uart driver too on Zephyr (It's my first time in developing drivers).
1.So what is the difference between a serial driver and a tty driver?
Is there any interdependence relation between them? I mean to write a tty driver should I write by first a serial driver, that will be a base to the tty driver or what?
So what is the difference between a serial driver and a tty driver?
A serial driver makes no assumption about the kind of device attached, it merely sends and receives raw "bytes" (see note), and probably offers some way to configure the communication (which baud rate, how many data bits, what kind of parity scheme, what kind of flow control, etc). The device attached to the serial port could be a serial mouse, or a bar code scanner, or a printer, or ... - the serial driver doesn't care.
Note: "byte" might not be a synonym for "octet" - e.g. it could be a group of 7 bits.
A TTY driver is tied to the assumption that the device is an type writer with a keyboard. Note: For the history; before computers existed we went from "people waving flags at each other" (semaphores) to "morse code with a single key" (telegraph) to teleprinters/teletypewriter (see https://en.wikipedia.org/wiki/Teleprinter ); and when computers got invented the (mechanical/electric) teleprinters were simply replaced with (computerized) dumb terminals.
Mostly; TTY is all about what bytes mean (and doesn't care much how the bytes are sent/received); and a serial driver is all about how bytes are sent/received (and doesn't care what the bytes mean).
Is there any interdependence relation between them? I mean to write a tty driver should I write by first a serial driver, that will be a base to the tty driver or what?
Crudely; a TTY driver has IO in 4 directions - getting key press info from local keyboard, sending bytes to remote whatever, receiving bytes from remote whatever, and putting characters on the local screen. For sending/receiving bytes with "remote whatever" you can use a serial driver; but (especially during development/testing) you could use anything else (TCP/IP stream, pipes, file IO, ...) instead - you don't necessarily need to implement the serial driver first.
Regarding your questions:
So what is the difference between a serial driver and a tty
driver? Is there any interdependence relation between them? I
mean to write a tty driver should I write by first a serial driver,
that will be a base to the tty driver or what?
It all depends on your operating system.
Previous answers relate mostly to Linux/Windows. You don't provide more points about it, but I'm assuming your question relates to Zephyr RTOS Project. I also assume you're developing a BSP for a custom board not yet fully supported by the RTOS.
The device driver model in Zephyr is different from Linux's or Window's driver models. You can take a look at the board porting guide and architecture porting guide.
The documentation contains a lot of samples, including quite a few of driver samples.
You'll also find more information here covering how to have access to support from the community.
I am trying to learn Linux by following instructions in "Mastering Embedded Linux Programming" by Chris Simmonds. By following the book and with some help from Stack_Overflow_1, i was able to build the MLO and u-boot.img.
However, when i connect USB cable to my PC and execute the ls /dev/tty* command, i cannot find any device with /dev/ttyUSB. All i can see are devices with /dev/tty0-63, /dev/ttyS0-31 and one /dev/ttyprintk.
Also, when i press down the S2 button and connect the USB cable, i can only see the power led glowing and nothing else.
I have properly built the u-boot (three attempts to get it right).
Also, as per the instructions in the book, i am only testing the u-boot stuff and yet to reach the kernal part.
If i remove the sd card and connect the USB, im an able to talk to my BBB over ssh (192.168.7.2).
How to i get the u-boot to work? Thank you!
If you don't have one yet, I'd recommend to get a USB-to-serial device (3.3V Vref). You connect it to the debug UART (J1) which is located next to the P9 side. Nowadays those are very cheap and can cost below 1$. Ones that feature a genuine FTDI part will be 5-10$ at least.
The serial port you are referencing is only available once the device has passed through U-Boot, booted the kernel and finally userspace has set up the communications.
Especially when working with U-Boot and the Kernel, low level UART access is crucial.
As a further note, could it be that the Book refers to the (white) original Beaglebone? That has a FTDI USB-to-UART chip on board and will allow you even U-Boot access. You can do the same things if you have the above mentioned USB device.
https://groups.google.com/g/beagleboard/c/eNDjK05spY8/m/GPvhcP52BAAJ shows that one needs to hold the space key to enter u-boot.
Also, the info. here might be more up to date compared to the book.
https://www.digikey.com/eewiki/display/linuxonarm/BeagleBone+Black
There is no way to copy and paste everything from the eewiki. I just left you the link. Enjoy!
I am programming a MAX32 Micro controller in MPLAB. I want to use the UART protocol to interact with my terminal (I am developing on a mac). Is this possible? Can someone point me in the right direction to get started?
Read Wikipedia UART Article
Read Reference Manual of your µC, Chapter "...UART..."
Get example Code for this issue from your Reference Manual or Programming Manual or Internet Articles
Program your board
Connect your Board with your PC via Cable (USB, RS232 to USB (virtual RS232) or UART to USB)
Open Terminal Program i.e. TeraTerm
Check your Settings i.e. Baud Rate
Try it
I am a begineer in learning Device Driver.I am practising with simple example to learn device driver. Can anyone suggest me how to start writing uart ,GPIO device driver for raspberry pi,because i started practising with raspberry pi only.
Thanks in advance
Regards,
pradeep
If this is your very first driver, start with something simple. I would take the following steps:
Write a simple character device driver that implements read/write/open/close file ops. That means they can be used with 'cat' and 'echo'.
Based on the initial work from 1, you can write a GPIO driver. This should be simple because all you need to do is write or read a 0 or 1 from a specific memory address.
Now that you have some experience with device drivers you can write a tty driver for your uart. There are lots of examples of tty drivers in linux already.
I am doing IO programming in C in Ubuntu. And I need the base address of the port to write data.
My laptop dont have a parallel port. So I bought a USB to Parallel port connector. I plugged in the device and its getting detected in /dev/usb/lp0
I ran "lsusb" to see the list of devices and I can see the ID also. But how can I get the base address ? For the usual hardware parallel devices, the base address is 0x0378. this address is not getting detected while using USB to Parallel device.
Please help.
A USB parallel port doesn't have a base address - it's not a meaningful concept for USB. I'm afraid the days of doing I/O on PC hardware via in and out instructions ended a few years ago, though lots of old tutorials still survive on the web.
You can write bytes to the parallel port as a character device, and these will appear on the printer port pins. The USB adapter will expect the other end to handshake data exactly like a printer. If you want to do general I/O prototyping, you're probably better off with a simple USB microcontroller like an Arduino.
Further discussion here.
If you are still interested to use this USB-to-parallel-printer device for your own bit-banging, it's important to know that their built-in firmware always allows controlling of D0..D7, INIT (as outputs), /ERR, ONL, PE (as inputs), but never for /ACK, BUSY (inputs), /STB, /AF, /SEL (outputs) pins.
And you need an 8-bit latch (e.g. 74HCT574) for catching data while strobing.
See here (https://www-user.tu-chemnitz.de/~ygu/bastelecke/PC/USB2LPT/faq#DIY)
especially for possible data rates.
Accessing from software side is a bit complicated but possible, and you may have to re-structure your software and hardware for making such adapters useable. I don't know for Linux case how to access, but IMHO you don't need to write a kernel-mode driver.