15

I finally solved this, but in a pretty unorthodox way. I abandoned bit-banging as too unreliable and tried to find other solutions which would allow me to the same thing without adding more hardware. I was considering writing a kernel driver, which would trigger an interrupt on GPIO and then reconfigure the pin to be SPI and use SPI to read an entire data ...


11

To me it looks like ser.write(1) has an implicit conversion to string. So your 1 becomes a "1" which is 00110001, which perfectly fits into your observation.


10

It would seem that atleast without the real-time patches (CONFIG_PREEMPT_RT), the Raspberry Pi cannot reliably bit-bang a 9600 baud serial. I used a simple latency tester which configured all the linux side things optimally (sched_fifo, priority 99, cpu_dma_latench 0us, mlockall). I tried sleeping for 100 µsec (roughly 9600 baud) and checking the latency ...


6

Cursory look over your code makes me think there might be a performance problem with the way you have interspersed your file writing logic with your acquisition loop. I am referring the fprintf statement in the acquisiton loop. My hunch is OS provided file buffers are getting filled due to the repeated fprintf and at some point fprintf blocks until the ...


4

As one of the commenters pointed out, using a native/hardware I²C implementation is much preferred, as the produced I²C signals would be much nicer (read: compatible). The CPU load would be negligible as you do not have to busy wait to produce delays, and often faster (400 kHz is one standard speed). However, bit-banging is useful sometimes, when you ...


3

I wrote a C++ library called v3c-raspi. You can download it from SourceForge. I wrote an example program that tries to do just what you want, called "i2s". Unfortunately it experiences a "program anomaly" anywhere from straight away to a couple of seconds after it starts - it looks like something else uses dma channel 0 and leaves rubbish in the block ...


3

I do not remember why the limit is 250k rather than say 500k or 1000k. I expect there was a reason. It may simply have been there was too much jitter at the higher bit rates to reliably clock the data. I suggest you have a look at the code and examine the consequences of changing the constant PI_BB_SER_MAX_BAUD to 1000000.


3

1) Bit banging just means using software rather than hardware to implement a communications protocol. To bit bang I2C this means to control the SDA and SCL signals in software. SDA is connected to GPIO 2 (pin 3), SCL is connected to GPIO 3 (pin 5). Generally to bit bang you need to set the GPIO high (write 1) or low (write 0). All the Pi GPIO libraries ...


3

You can toggle a gpio at around 25 MHz. I expect you could get perhaps a tenth of that if you were to bit bang. Of course that really depends on what you are bit banging. For general information see http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/raspberry-pi/gpio-pin-electrical-specifications


2

That LDAC signal is truly nasty. I have read the datasheet and your messages a few times and I can't quite focus on a specific issue so I figure out you're just brainstorming. I will start from what I know from direct experience. How should I write this communication to be as orderly as possible - should I write special C routines within my Python ...


2

A few thoughts: Using dedicated I2C pins for your bit-banged I2C should be fine as long as you don't use smbus at the same time. Improving GPIO timing in userspace can be done by increasing process priority (see man nice). Re-writing your bit-banging routines in C will help on average, but the worst case will be just as bad as with Python. The only way to ...


2

Question I2C device reading writing errors problem. How to solve it? Answer There are many reasons causing reading and writing errors. To name a few: Wires too long (more than 30cm) and not twisted. A suggestion is to use twisted cable Cat 5 to reduce mains EMI noise picking up, I2C speed too high. A suggestion it to start testing a low speed, such ...


2

The solution is to bridge the RPi GND and 3v using a cap. I used a 1uF cap.


2

UmaN the sparkfun product description says "RHT03 (also known by DHT-22)" So finding the information you require should be much easier. Driver adafruit's github repo Has the "driver" written in python. So you can use the sensor with your PI. They also have instructions on how to set it up. Arduino library: https://github.com/adafruit/DHT-sensor-library ...


2

To avoid flickering of the segments, you really do need hard real time control of the multiplexing. Even small variations in the timing will be quite noticeable. Using the timer on the CPU should work quite well, but as you observed it seems a lot of hassle for one simple thing. Perhaps it's worth doing if it's not just a one-off thing you are making. ...


1

What do you mean by at once? You can buy two TCA9548A I2C multiplexors which will allow you to connect 16 MPU6050 on the same bus (at the same bus address). However only one MPU6050 may be addressed at any one instant in time.


1

That appears to be a DHT22 sensor using a different brand name. Try my http://abyz.me.uk/rpi/pigpio/examples.html#pdif2_DHTXXD software.


1

Just see this. Raspberry-Pi-DMA-Example https://github.com/Wallacoloo/Raspberry-Pi-DMA-Example


1

Using DMA bit banging it is possible to get accurately timed gap-less samples from the MCP3202. The same technique should work for the MCP3201 with the obvious change to the SPI command to request the data. The MCP3202 (12-bit ADC 2 channels) command SPI tranfer is 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 SB SD OS MS NA B11 B10 B9 B8 B7 B6 B5 ...


1

the data acquired has unaccounted gaps in it I think "accounting" for them is simple enough, it is arbitrary latency. If the units there are seconds, then that is a cause for consternation. If they are centiseconds or smaller, that's the nature of the beast on a multi-tasking OS. You're not going to be able to guarantee yourself zero-latency, although ...


1

I have a very similar scenario as you: A distributed domotic system all over the house with a central device (Raspberry PI) and a few satellite boards with I2C (PCF8574/PCF8591) and 1-Wire (DS18B20). Everything is connected via ethernet cat5e cables. To allow long range I2C communications I'm using the P82B96 I2C bus expander. For 1-wire communication is ...


1

Are you sure that you have the right value for RGB_ADDR? Whenever I have seen a -82 error with pigpio it has been because the I2C chip is not responding. This is usually because you are using the wrong address. Another possibility is that SCL/SDA are swapped. Note that the data array expects a 7 bit address and pigpio automatically appends the correct ...


1

The Raspberry Pi isn't really suited for this application. You'll need to use hardware timers and pin interrupts to do it right. To receive a message on the bus, each part of it must be acknowledged or the transmitting node will give up and not send the rest of it. That means you can't read anything without writing a zero bit at precisely the right time. ...


1

If I understand correctly what you are trying to do then there is a simple software solution. The following Python code should update multiplexed 7-segment LCDs in a flicker free way. For testing purposes each LCD is updated for 100000 µs in turn. In a practical application a value like 1000 µs should be used. The period is set by the REFRESH constant. ...


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