标签: devices

Industrial systems typically require data acquisition and processing in real-time. These systems could range from a simple lighting control system to a large distributed control system comprising of sensors/actuators, gateways, monitoring and processing units. Designing such an embedded system puts forth a lot of challenges for design engineers in terms of striking a balance between low-end microcontrollers to performance oriented processors. This can be addressed in an optimal way if the design is done keeping the complete system and its end goals into consideration. I’ve put forth here a high level approach to overcome these challenges using various system resources to enhance the performance. The System We were designing an industrial data acquisition system and had constraints in terms of the total product cost. We opted to go with a TI-Sitara processor with ADC and DAC connected over the SPI bus. The system also has the Digital IO expander connected over I2C based IO expander.  The system runs on Linux Operating system (with RT patch) with standard BSP Drivers for all on-chip peripherals.  The key aspects of the system are: - ●     System running Modbus client responding to the MODBUS master for read/write of system configuration and real-time data ●     System running Web-Server to allow the control/configuration of the system and monitoring of real-time parameters ●     Capable of handling up to 16 Analog input 16 digital input. ●     ADCs capable of capturing the input signals with the sampling rate of 1 KHz for each channel. ●     Digital input being monitored and state changes being responded within 10 milliseconds. System challenges The single largest challenge determined during the implementation and testing is associated with the capture of the analog input. To be able to capture the analog input at 1KHz for all channels, the ADC has to be configured for higher sampling rate of 16KHz. Since the ADC does not provide the buffering, all the captured data will have to be read immediately to avoid it being overwritten with new data corresponding to different channel. The ADC provides an interrupt after completing the conversion for each channel. The standard driver implementation would register the interrupt and initiate the read of the SPI registers. Incidentally, for reading the SPI registers, there is a need to perform SPI register write (so as to generate the required clock). Due to interrupt latencies of Linux (even with the RT patch incorporated), the ADC capture is being missed. Below is the representative summary of the flow of control and data. 1.    ADC completes the conversion and asserts the End of Conversion (EoC) signal 2.    The Sitara registers this EoC line as interrupt and invokes the Linux GPIO Interrupt handler 3.    The kernel space interrupt handler determines the source to be ADC and then accordingly invokes the ADC drivers 4.    The ADC driver in kernel space issue an SPI bus read and thus reads the conversion value 5.    The value is then given to the user’s space application for further processing. Owing to the large interrupt latencies, context switching time in Linux and the interaction between the kernel space and user’s space components, there was an overall delay. This limits the overall sampling rate. Systems approach Issues like the one stated above are likely to occur while various disciplines are working as islands; i.e., the hardware, BSP applications are working disconnected with each other having fixed interface plans. Instead, if the design is done keeping the complete system and its end goals into consideration, such problems can be solved in much optimal way. This is Illustrated below. The Sitara is a complex SoC having multiple features including DMA engines. These DMA provide multiple features including event based triggering and chaining. These features have been exploited to solve the above problem. Below is the outline of control and data flow. 1.    The EoC signal from the ADC is configured to trigger the DMA for issuing the SPI Write (so as to generate the clock). The clock also causes the ADC to transmit the converted data into the SPI lines all the way into the internal receive shift registers of SPI controller in Sitara 2.    Being full, the internal receive shift register triggers another DMA to read the data from shift register to the memory buffer 3.    Steps 1 2 are repeated for 16 channels. After 16 channels data is transferred to system memory by DMA, the DMA generates transfer completion interrupt 4.    The interrupt handler transfers the data corresponding to 16 channels and reconfigures the DMA for next transfer waiting for EoC 5.    The hardware timer is separately configured to generate the required Start of Conversion signal to ensure the sampling interval is deterministic. The ADC is configured to carry out all the channel conversion and stop (waiting for subsequent Start-of-Conversion signal). This approach yielded the following benefits. ●     The system load (CPU Load) is reduced as the Sitara is no longer executing the interrupt handler for every channel conversion completion ●     The reliability of the sampling rate is hardware timer controlled and thus immune to variations on the CPU load ●     Able to achieve greater sampling rates reliably. Thus, as showcased above, a thorough understanding of the SoC and its features and seamless integration between the hardware, BSP and application are key to a successful optimization of System performance optimization for a variety of embedded devices. Contributed By, Sachidananda Karanth, Senior Technical Architect - Software Design, Mistral Solutions Pvt. Ltd.

在网盘上： http://pan.baidu.com/s/1kTEA2fd    

Mobile devices   Mobile devices are susceptible to the damaging effects of Electrostatic Discharge (ESD). In addition, mobile devices, because of their higher operating frequencies, are more sensitive to EMI/RFI interference. Transient Voltage Suppression (TVS) devices provide protection at board-level from the effects of ESD as defined by IEC 61000-4-2. When used with the proper shielding, these devices provide additional EMI/RFI filtering. Mobile devices in today's market include high resolution color LCD displays. These displays require high bandwidth, low noise data lines, to prevent unwanted noise that can interfere with the displayed image. CitrusCom's ESD+EMI filter array offers maximum attenuation filtering and protection from ESD, while allowing high-speed data signaling from the baseband chip-set to the LCD display. The device achieves better than -30 dB of attenuation, at frequencies from 800 MHz to 5 GHz, with no line loss. With a high cut-off frequency, the ESD+EMI filter is ideal for filtering and protecting the LCD interface. CitrusCom offers EMI filter arrays in four-channel, six-channel, and eight-channel versions to provide optimal reliability and design flexibility.

Till recently, connectivity used to be about being able to connect to the internet. Whether it was from a notebook, a tablet or a smartphone it was about being connected to the rest of the world. Over the past three years that has changed dramatically. Don’t get me wrong, being able to connect to the net is an important and fundamental requirement, but we also want to be able to connect to the things around us. Where did I hear this recently…”Big things have small beginnings!” I am a slave to my smartphone. It’s my alarm clock, my email, my entertainment, my reminders all rolled into one. I hate to admit this, but the first thing I do when I open my eyes in the morning is to reach out to my phone and check my email. I no longer have a newspaper subscription, I read the news on my phone. Twitter, facebook, linked in all there. But these are examples of being able to connect to the network and get stuff that is happening out there. I have a banking app, an app for what movies are going on, travel…all of it. The phone goes everywhere with me. It’s a welcome weight in my pocket, and I cant put it down. One of the first thing that I check when I get up to go somewhere is do I have my phone with me. But then you already know all of this. Maybe you are a little like me when it comes to your phone too. This post is not about the ubiquity of the smartphone, but how things are changing… From being my little window into the world, my smartphone has become my remote control to the world. I have a little device installed in my home, the Peel remote, it’s a little dongle that is plugged into my home network which talks over ZigBee to a small fruit that sits on my coffee table (actually I mounted it on one of my home theatre speakers). http://store.apple.com/us/product/H4714LL/A It’s a program guide application that tells me what’s playing on TV at any given time, and using the peel application I can say “Watch on TV”. That turns on my TV, my set top box, my home theatre. All from my smart phone. I have an Apple TV; and all of my music is either on my home PC or on my phone. Connect to apple TV and voila I have my music. I’m watching a video on youtube and I think I want to show it to somebody, play it on my TV. I’ve become a bit of a exercise fanatic, so I have two tools of the trade…a nike + ipod http://en.wikipedia.org/wiki/Nike%2BiPod. It tucks into my shoe (ok I cant afford the Nike + shoe and have a little pouch that attaches it to the top of my shoes!), and a heart rate monitor. It logs my steps, my speed (on the treadmill) and my heart rate. It tells me when I am pushing it too hard, and when I am pushing too little. I hear that there is a device available that will track my sleep; a weighing machine that my phone can connect to to log my weight; a BP machine that will log my Blood Pressure to my phone, which will then log it online for me; I want them all! And I suspect I am not alone… I’m still waiting for a good watch that has the battery life and supports bluetooth connectivity so that when I get of the plane in a new place, new country, my watch is telling the correct time. Do I really really need this? Maybe not. Am I happy to have this information with me? Definitely! Are these small things…definitely, but there are big things too. Imagine a doctor walking up to a hospital bed and with a tablet in his hand (not the swallowing kind!) he/she has a view into everything connected to you. Your smart phone is your key to the door, your mobile wallet and a whole lot more.   I’m a techie, I like to use technology. I also have the pleasure of being part of building it in the first place. A few of the things I listed above, Mistral has been a part of! Ah yes…I remember where I heard that quote I put in the beginning of this post, in the trailer for the movie Prometheus…Oops!    ​- Samyeer Metrani