I want to write a program to read a status of a GPIO pin (whether it is high or not) specifically using c++. I know that I have to export it by writing a value in sys/class/gpio and then set its direction as "in". Now I am confused on how to access the interrupt generated on a GPIO pin and do some action in my code with respect to that input.. I dont want to use any custom made library functions.
Thank you.
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I just started with microchip world.
I'm about to buy a PicKit3 and i've seen it can outputs from 1.8V to 14V MCLR.
The pic i will use is the PIC16F1829 and it should work with MCLR # 5V.
In the datasheet it seems i would need a zener/shunt to limit the voltage.
First of all isn't there a board ready to play with?
Can i use LVP? If so using MPLab 8 IDE how do i change in LVP?
Is the pin connection the same?
Since i haven't bought it yet i would rather avoid burning a pic
Regards,
Notes at the bottom of page 345 in the PIC16F1829 data sheet (DS40001440E) recommends using a voltage limit circuit when using the ICD2 device programmer.
According to Microchip this is "not required" when using the PICkit3.
Get a few extra PIC16F1829 just in case.
You ask about boards ready to use, take a look at the Curisotiy Nano boards
https://www.microforum.cc/topic/9-microchip-xpress-evaluation-boards
These are ready to use and do not need any programmer. You can simply send a file to these devices over USB. They are also have debugging capability.
In terms of the 14V on MCLR, the device is designed to handle whatever pulse will be generated by the PICkit3, so you do not need any protection for the PIC against that. In fact limiting the voltage on that pin will prevent the device from programming so you definitely do not want to do that. If you are however using this pin to connect to other parts on your board the other parts probably will need protection.
You can most definitely use LVP, just be careful, it is possible to use LVP to disable LVP, and then the only way to get it back on is to use HVP!
Lastly in the IDE under programming options you can change the mode there (Use low voltage programming mode entry)
In the IDE i've set the voltage appropriately and everything went ok on its own.
I didn't have to enable anything fancy
I have been unable to find any documentation regarding using python to change the GPIO outputs, and was wondering whether there was any specific code i could use to change it or if there were any third party programs that allowed me to do so.
You cannot change the current of GPIO pin, that's not how it works.
If you want to know the maximum value of current for GPIO pins, this article says it's 16mA per pin, with maximum of 51mA for all pins.
Coming form this question yesterday, I decided to port this library to my board. I was aware that I needed to change something, so I compiled the library, call it on a small program and see what happens. The 1st problem is here:
// Check for GPIO and peripheral addresses from device tree.
// Adapted from code in the RPi.GPIO library at:
// http://sourceforge.net/p/raspberry-gpio-python/
FILE *fp = fopen("/proc/device-tree/soc/ranges", "rb");
if (fp == NULL) {
return MMIO_ERROR_OFFSET;
}
This lib is aimed for Rpi, os the structure of the system on my board is not the same. So I was wondering if somebody could tell me where I could find this file or how it looks like so I can find it by my self in order to proceed the job.
Thanks.
You don't necessarily want that "file" (or more precisely /proc node).
The code this is found in is setting up to do direct memory mapped I/O using what appears to be a pi-specific gpio-flavored version of the /dev/mem type of device driver for exposing hardware special function registers to userspace.
To port this to your board, you would need to first determine if there is a /dev/mem or similar capability in your kernel which you can activate. Then you would need to determine the appropriate I/O registers for GPIO pins. The pi-specific code is reading the Device Tree to figure this out, but there are other ways, for example you can manually read the programmer's manual of the SoC on which you are running.
Another approach you can consider is adding some small microcontroller (or yes, barebones ***duino) to the system, and using that to collect information from various sensors and peripherals. This can then be forwarded to the SoC over a UART link, or queried out via I2C or similar - add a small amount of cost and some degree of bottleneck, but also means that the software on the SoC then becomes very portable - to a different comparable chip, or perhaps even to run on a desktop PC during development.
I am looking to enable external interrupt on the rising and falling edge of a GPIO pin configured as input on Beagle Bone. How do I go about doing this? I know how to use GPIO's using the /sys/class/gpio and /dev/mem method. Can anyone tell me what piece of code do I need to write to make the code jump to an interrupt handler on a certain input event on the gpio pin?
Thanks!
I am looking into the fpga driver code which will write some value to FPGA device at low level. At top level in user space value is being written to /dev/fpga, now I guess this is the logic how driver gets its value from user-space and exposed file in user space is "/dev/fpga".
But now how actually this value from fpga is reached to device , there must some callback maintained.
But I really could not figure out how it actually happens,Is there any standard way?
Anybody can help me find out this userspace to kernel space link.
It's probably a character device. You can create one in your kernel module, and your callback functions will be called in the kernel when it is opened, something is written to it etc. See:
http://linux.die.net/lkmpg/x569.html
for an explanation how it works and sample code.