We are doing research into running a server on a Pi, and communicating with it via a webapp (over a local network) to control 2-3 servos. It appears that the Rpi has only one hardware configured PWM pin, but this can be worked around via servoblaster. However, since Servoblaster utilizes the Rpi's DMA, will it interfere with the Pi's ability to operate a web server? I apologize if this question is unclear i am somewhat unfamiliar with the software/network concepts involved. Additionally, is there a good resource for understanding the DMA function further?
Thanks in advance for any help.
You can control Servos using Software PWM, which will not require any further hardware or using DMA
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I am working on edge computing for IoT applications and expected to create a system that acts as a near edge computer with the use of a raspberry pi hooked up to a dht11 sensor. How do I send this data over to a computer that is at the edge? Ideally I want to use my PC as this device but I have no clue how to send this data over in real time.
So far I have created the circuit and can view the temperature and humidity readings on the raspberry pi in python. Unsure of what the next steps are - I don't want to send this data over to the cloud just yet.
Side note: I believe i may be missing knowledge regarding this but is the raspberry pi an edge device because it is hooked up to the sensor directly?
Any help is greatly appreciated.
You need to think this through a bit more. What will you do with the temperature and humidity data that you receive?
For example, if you're just experimenting and want to just see the readings in a console on your PC, you can use netcat to send the console output of your Python program from the RPi to PC. No SW development needed, they just have to be in the same network. Not particularly useful for anything else, either.
Otherwise you need to set up some client-server solution between the RPi and your PC. There's a ton of possible solutions, all depending on what you plan to do with the data. You can use MQTT, HTTP, a straight database connection (MySQL, PostgreSQL), etc. You have to supply both sides of the connection. The Python code on client side which connects and sends data; and the server side thing that accepts the samples and stores them somewhere. Plus all the networking, authentication etc.
Or you can just download the Python client libraries for your favourite cloud solution and set that up according to a tutorial. TBH, this sounds a lot less work to me.
I want to make a network camera, stm32 through the camera to collect images, and then sent to the server through the WIFI module. As 1 second need to transfer a lot of data, so I would like to use the USB interface wifi module program to achieve. Or what better solution to achieve.
Thank you!
I think that you have no idea how the USB works.
You have a couple solutions.
Use a wifi module with SPI interface.
Use a SOC like CC3200.L
Use ESPxxxx module or similar (RTL8710)
You can of course try to use STM with host usb interface, but you will have to implement the USB host stack + driver for USB wifi module + network stack (eg TCP/IP stack). But it is quite complicated as the STM ones are not very good, there are some better paid ones - but expensive. USB host is not easy to implement.
If you want to go along the "networking over USB" path on STM32 (and I'm assuming you're not planning to buy any commercial drivers) it's going to be rough for you.
When it comes to USB, vast majority of the WiFi dongle drivers are proprietary and unless you're on an operating system such as Windows or Linux you're out of luck, unless you want to for the reverse engineering or porting at least parts of the drivers from Linux. With the USB you can think of using the USB-ECM (ethernet over USB) class, but two things here. One - ST doesn't provide any free implementations of this class so you're down do searching for it or implementing it yourself. After a bit of googling I've found one instance of this on githbu, although I havent tested it myself. Second thing - this is no longer wireless as you'll need to be connected to some kind of host providing internet connection, at which point it's probably better to not use USB-ECM and networking at all and just send data using a class that can be implemented easily (USB-CDC or USB-HID). I'm a bit worried about the throughput here.
You can also try to find WiFi modules that are connected over other interface. Generally those modules are connected over UART, some over SPI. This way, integrating it with the TCP/IP stack will also be up to you, at least when it comes to implementing the WiFi module protocol (most likely AT-commands) and implementing network interface so that the stack can "talk" to it. In this approach, I'm almost sure that you'll lack the throughput required for your application.
Personally I'd strongly suggest trying Ethernet if that's an option for you. It's going to be highest bandwidth (which you're going to need), plus it's most "out of the box". There's multiple projects implementing various applications using a free LWIP stack over this interface, including examples generated by ST's CubeMX.
How to reset PC(motherboard) from FPGA on PCI board (without BIOS manipulations)
Subj.
You are probably not going to find a scheme that works with all motherboards, if you even find any. Intel and AMD do this differently too. If you're lucky to find a motherboard where the PCI reset signals are open drain you might be able to drive it and cause some bad stuff to happen and cause a reset. If the motherboard drives those signals then you are out of luck (you could damage the driver).
You could also try to crash the system that would cause a reset, although that's getting harder nowadays with PCIe. Operating systems seem to be able to survive bad PCI devices due to better error handling and timeouts, etc.
Is this to implement some sort of watchdog? Probably easier to do this using IPMI and some sort of heart beat.
I need a product to simulate network latency for testing mobile applications (in particular iphone and android). I plan to set up a wifi router connected to a linux box, and write a number of scripts to approximate different types of connectivity issues.
So far, I've taken a cursory look at Netem and ns-2 (or its offspring ns-3). Netem looks very easy to deploy and configure, but they both look like they'll require some in-depth investigation.
Does anyone have positive/negative experiences with either of those solutions that they could share? Or maybe used a different solution for this problem?
If anyone comes here looking for tips, I've found a solution that seems to work well.
Ubuntu comes with Netem installed, so I went ahead and just made use of that. Basically, I got a computer with two ethernet ports, forwarded one to the other and applied Netem latency settings to the connection. Then I attached a wireless router to one, and LAN to the other. Netem lets me play with all kinds of latency and packet loss settings.
Btw, I also tried to use a few different laptops and set the internal wireless card up as an ad-hoc wireless router. I got it working for the most part, but finding a laptop with an internal wireless card that plays nice with ad-hoc in Linux is tricky at best... can't recommend it.
I have a NIC card and a HDD both connected on PCIe slots in a Linux machine. Ideally, I'd like to funnel incoming packets to the HDD without involving the CPU, or involving it minimally. Is it possible to set up direct communication along the PCI bus like that? Does anyone have pointers as to what to read up on to get started on a project like this?
Thanks all.
Not sure if you are asking about PCI or PCIe. You used both terms, and the answer is different for each.
If you are talking about a legacy PCI bus: The answer is "yes". Board to board DMA is doable. Video capture boards may DMA video frames directly into your graphics card memory for example.
In your example, the video card could DMA directly to a storage device. However, the data would be quite "raw". Your NIC would have no concept of a filesystem for example. You also need to make sure you can program the NIC's DMA engine to sit within the confines of your SATA controller's registers. You don't want to walk off the end of the BAR!
If you are talking about a modern PCIe bus: The answer is "typically no, but it depends". Peer-to-peer bus transactions are a funny thing in the PCI Express Spec. Root complex devices are not required to support it.
In my testing, peer-to-peer DMA will work, if your devices are behind a PCIe switch (not directly plugged into the motherboard). However, if your devices are connected directly to the chipset (Root Complex), peer-to-peer DMA will not work, except in some special cases. The most notable special case would be the video capture example I mentioned earlier. The special cases are mentioned in the chipset datasheets.
We have tested the peer-to-peer PCIe DMA with a few different Intel and AMD chipsets and found consistent behavior. Have not tested the most recent generations of chipsets though. (We have discussed the lack of peer-to-peer PCIe DMA support with Intel, not sure if our feedback has had any impact on their Engineering dept.)
Assuming that both the NIC card and the HDD are End Points (or Legacy Endpoints) you cannot funnel traffic without involving the Root Complex (CPU).
PCIe, unlike PCI or PCI-X, is not a bus but a link, thus any transaction from an Endpoint device (say the NIC) would have to travel through the Root Complex (CPU) in order to get to another branch (HDD).