People,
I have always seen references about how to use a SPI interface to operate a SD memory card.
This is not what I want. I need to do exactly the opposite.
I want to be able to use the SDIO controller (through SD slot) in my "host" (any PC having a SD-card interface) to talk to my devices (basically microcontrollers) that can only "speak" SPI.
If my understanding is not too wrong, I cannot simply tell my SD controller to talk in a raw SPI mode but I can teach my microcontrollers to behave as a SDIO device that can be controlled by my host.
This way I still have two challenges left:
Correctly implement a generic SDIO device in my microcontroller.
Implement/configure the correct drivers in the host to be able to interact with my devices.
Implement the SDIO device seems to be a matter of following the spec.
The host-side driver, though, is something I hope I can accomplish with a user-space driver in Linux using some already existing kernel-space driver to SDIO.
That's the point that I come to ask for help.
Can anyone please point me any samples, documents or any kind of resources that can help me in my task?
On the PC side, this is all you need: http://sourceforge.net/projects/sdio-linux/
This may be useful for reference: http://www.varsanofiev.com/inside/WritingLinuxSDIODrivers.htm (although, I don't think you would be writing a driver)
On the microcontroller side, use "bit-banging" to implement the SDIO spec.
However, first consider why do this. SDIO and SPI are just serial protocols, so is USB; wouldn't you rather make an SPI-to-USB bridge? USB is much more user-friendly on the host side, as well as being more standard/more common. And if you do want a SPI-to-USB bridge, turns out it already exists, the SPI Shortcut (probably other options, this is just the first one that comes to mind)
EDIT Or, you could bit-bang I2C on the micro, if the host supports I2C (many do). Actually, go through every serial protocol the host supports, and see if you can support it easily from the micro side (by bit banging, since the micro is likely to not have a slave mode for that protocol built-in). RS232 (with level shifter), I2C, and SPI are likely to be the preferred choices. SDIO is pretty much the last choice, I think.
SDIO is very tightly specified. Unless your microcontroller has an SDIO block that is designed to act as a device rather than host, I don't think this will be possible. I know of a few special purpose communications controllers that implement an SDIO device, but I haven't come across any general purpose microcontrollers.
You would need a fairly fast microcontroller to be able to bit-bang SDIO initialization at up to 400 kHz. If running an STM32F4 at 180 MHz, this gives you only microcontroller cycles between SDIO clock cycles. If the host turns up the clock speed to the maximum of 25 MHz after initialization, then you're down to 7 cycles between SDIO clocks.
For perspective on the SDIO spec, the one you linked is a simplified spec that doesn't cover the signalling and timing of the bus. The full spec is many times larger.
As Alex I mentioned, there may be better alternatives for what you need. If your SDIO host supports SPI mode, most microcontrollers do have SPI peripherals that can act as slaves rather than hosts, so this may be an avenue without a peripheral. If your data rates are low enough, a simple UART may suffice (you can reasonably hit 1 Mbit over short distances).
Related
I have a hardware device that consists of 3 separate chips on an I2C bus. I would like to group them together and expose them to userland as one logical device. The user would see the logical device represented by a single directory somewhere in /sys as well as the nodes you'd expect from the I2C chips under /sys/class/i2c-adapter/i2c-?/*.
One of the chips is an MCP23017 which as far as I can tell already has a driver (drivers/gpio/gpio-mcp23s08.c) and I'd like to reuse it. Another of the chips is a PCA9685 and I would like to contribute a driver for this chip that uses the PWM system in include/linux/pwm.h. The third chip is an MCU running custom firmware.
How should I structure the set of drivers? One idea I had is to register a platform driver to present the logical device, and use I2C drivers from within that. Is this a good way to go? Are there better ways?
The logical device is a motor driver board and IR receiver. I have a simple diagram of its structure.
I'm looking to create two interfaces. The first similar to /sys/class/gpio where motors can be 'exported' and then accessed via reading and writing attributes. This would be useful for shell script access and quick debugging of the mechanical parts of the system attached to the motors. The second a character device node in /dev where data can be read or written in binary format, more useful for application control.
it seems not usual design, are you sure you have access to I2C bus of all chips ?
I think you should be able to talk only to MCU, and MCU should manage other devices.
Otherwise, why MCU is there ?
However, I cannot see your diagram, perhaps link is wrong.
In Linux, HAL provides hardware abstraction and device driver too provide hardware abstraction. Can you please clarify me the difference between two ?
The device driver communicates with a specific device at a specific buffer and control flag block location. A hardware abstraction layer abstracts away the details of how specific devices work. For example, the driver for a USB mouse is very different from the driver for a PS2 mouse but at the HAL layer they are both mice and can be treated interchangeably.
I would say that HAL provides hardware abstraction using device drivers. From a certain point of view, no device can work without a driver. HAL goes one step ahead, offering a uniform (or, "easier") API for the application.
You can bypass HAL and talk directly to the device driver, but you can not bypass the device driver and talk directly to the hardware (this last sentence is more or less valid in general, depending on OS and environment).
The main difference is what they provide abstraction for. HAL abstracts processors, device drivers abstract different devices. So in a sense HAL is the "device" driver of the processor or the motherboard in PCs.
Back in the day, every programmer who coded an app also codes drivers for the various hardware that they wanted to support. So, if you have an idea to develop an app which needs to use network capabilities, you also needed to know how to program hardware drivers for the network card. Then came in the HAL.
So instead of having your software and OS directly reaching out to the hardware, there is now a layer in between called the HAL. The HAL lies underneath the operating system layer or within.
Now nobody is allowed to access the hardware, except that they do it through and by the hardware abstraction layer(HAL). Just the HAL is allowed to access the hardware.
Now it's something which is standard. All Devs have to do is make the game/app work with the HAL.
Now we have the drivers. The drivers tell the HAL how to access the actual hardware.
So whoever makes the sound card, they just make a driver that tells the HAL how to access that sound card.
So overall, our software interacts with the HAL, The HAL uses drivers to interact with the hardware. We are telling the HAL how to access that sound card or network card etc. with the use of the drivers.
I want to implement a driver in Linux, that has a Ethernet stack but the data going out on hardware will be a serial port. Basically, I want to register my serial port as a Ethernet driver. Does anyone have any idea if this is possible?
I want to be able to push IPv6 and/or UDP packets out of the serial port and in a similar way receive the packets via a serial port and pass it up the Ethernet stack.
I do not want to use the solution of serial-to-ethernet convertors(external hardware that convert a serial port to a ethernet port) but have that in my PC itself.
I tried PPP over the serial port and it works well. I am also told that I can do FTP, HTTP etc using the PPP. Reference to this - http://www.faqs.org/docs/Linux-HOWTO/Serial-Laplink-HOWTO.html
I have tried to hack the code from a RealTek Ethernet driver with a serial driver but not able to gain much success. Rather I do not know the stack of either to actually do anything meaningful. Any advice, guidance or tutorials would be helpful.
Thanks
Aditya
You need to get back to de basics on networking, the way I understand you question is: "I have a serial port and I want to use is an Ethernet link". Sorry to crush your dreams but you don't have the real hardware to do so, I'll elaborate on it.
A serial connection is a physical connection that requires 3 wires (at least) tx, rx and ground. On the logical side you have an IC that coverts binary data into signals that are represented by discrete voltage ranges.
Ethernet is a layer 2 protocol, the layer 1 is provided by the technology used to transmit the signals (coax, up, fiber etc.) As you might see by now, you need a different set of hardware to convert the logical Ethernet frames into a stream of digital numbers, in fact this is call framing.
Since Ethernet has been an easy to use protocol it has been implemented as e preferred protocol for many network operators, of course one of the biggest is PPPoE where you have a PPP session over an Ethernet link. Of course this won't work with your example neither since you're trying the opposite.
If you're just learning and have all the time in the world you can attempt to write your own Ethernet framer over serial lines. This means you need to implement IEEE802.3 into the driver and then you need to serialize the data to push it as a stream of bits over the serial line. Of course note the following drawbacks:
Your driver won't be able to fully support Ethernet, you need some support at hardware level to implement some signaling (example, auto negotiation, CSMA/CD, etc)
You driver will be pretty much useless unless you back in time where 115.2kbps is top speed in data transfers
IMHO there are more exciting projects that you can pick up in the networking field for device drivers. You can for example attempt to buy a NIC and develop the device driver for it from scratch and you can optimize certain areas. Finally, remember that most of the Ethernet implementations are now done in hardware so you don't have to do anything but filling a few registers on the MAC and voila!
SLIP and PPP do already what you want.
I'm looking to implement the Bluetooth protocol over a physical Wi-Fi based transport, if that makes sense.
Basically my phone has Bluetooth, and my laptop has a Wi-Fi card (802.11a/b/g).
I know that Wi-Fi operates over the range 2.412 GHz - 2.472 GHz, and that Bluetooth operates over the range 2.402 GHz - 2.480 GHz.
I couldn't help but notice the overlap here. So my questions are:
What sort of low-level APIs would I need (preferably in C, on Windows) in order to send a signal out at certain frequencies on the Wi-Fi card?
Would I be able to implement a Bluetooth stack on top of this?
So basically, can I transmit Bluetooth using my Wi-Fi card as essentially a radio transmitter?
Thanks
Implementing the Bluetooth protocol over a physical Wi-Fi based transport does make sense!
Bluetooth high speed (v3.0) defines the possibility to use alternate MAC/PHY layers, known as AMP feature. The L2CAP and higher layer protocols from Bluetooth can be transmitted over a Wi-Fi MAC/PHY layer rather than a Bluetooth MAC/PHY layer with a resulting higher throughput. Some products are on the marked supporting this - look for 'Bluetooth High Speed', AMP or Bluetooth v3.0 support.
No, you can't do this. Bluetooth devices are typically wrapped up all in one chip. Plus, they use completely different modulation techniques. No low-level anything is going to allow you to transmit anything different, unless you are flashing the device. Even then, it may not get you much closer.
Bluetooth Modulation Information:
http://www.palowireless.com/infotooth/tutorial/radio.asp and http://classes.engr.oregonstate.edu/eecs/spring2003/ece44x/groups/g9/jon_gillen/white_paper_jon.pdf
About the only thing you can share between WiFi and Bluetooth devices is the antenna. (Assuming only one device is using it at a time... don't blast 32mW into the receiver of the other radio!) The radio itself is all wrapped up into the same chip. The same is generally true for WiFi.
Bluetooth and Wifi have different phy layer protocols and thats what is coded into their chips, hence you can't use one chip to transmit packets of the other protocol.
Moreover most of the chip vendors, do not expose any RF logic.
Technically yes but there are some things to consider such as the pre existing coding on the chip and if the chip can support Bluetooth coding as well as wifi coding, I mean if you have two separate wifi chips go ahead and try but be warned I tried and nearly killed my computer because of preexisting copyright protection coding on other parts of my pc that prevented any programs on the chip from starting until I reset the chip to factory defalts.
Does anyone know how a bluetooth device could pick up the discoverable devices' device IDs in range?
I am ideally looking for the simplest solution that involves the smallest implimentation of the bluetooth protocols.
A starting point would be good, I just wish to create a device that can store all the device ids of nearby bluetooth devices with minimal power consumption, preferably just using radio frequencies and not SDP and whatever else.
If you can't help me with this, please can you help me find good reading material for low level bluetooth (step by step) communication. The reading online is so high level that I cant work out what is actually sent, when.
Laalto nailed the answer from the Bluetooth spec/stack POV, but your question implies your looking for a stand-alone Bluetooth device - not just a laptop app scanning surrounding devices.
I can only speak for the BT chips that the company I work for manufactures (Cambridge Silicon Radio - CSR) but our chips can do that pretty much out of the box. Our chips have an on-board Virtual Machine sandbox that allows access to the firmware functions and Bluetooth stack of the chip. You can easily write a C code app to run in the virtual machine sandbox, on chip, that periodically scans for discoverable devices around, grab their ids and then download them when connected via USB or Serial, or maybe over BT when a device connects to the listener directly.
www.csr.com and www.csrsupport.com for chips, dev-kits, design references, etc.. etc...
You probably want a module with the extra HW (UARTs, USB etc...) as well as just the chip but you could implement this with something the size of a BlueTooth USB or probably smaller.
It would really help to know more about what your trying to achieve, why you want something that just scans the surrounding bluetooth devices and how big the device needs to be.
Sorry if this sounds like advertising. For balance: Broadcom make BT chips too!
The Bluetooth specs from http://www.bluetooth.org are a good starting place for low-level information. You need an account to access the specs, but you can create one for free.
Basically what you need to do is to go into Inquiry mode periodically and grab the response packets as they arrive. The more time you spend in Inquiry mode, the more likely you will discover devices in range: discoverable devices enter the Inquiry Scan mode only relatively rarely; it takes some time (10.24s at least with older Bluetooth versions) to scan all the possible frequencies in the Inquiry/Inquiry Scan frequency hopping schemes. And even then you can have suboptimal radio conditions.
For implementation I suggest you at least start with existing Bluetooth libraries such as BlueZ and do not attempt to create your own from scratch.