search

mattjlewis / diozero

Java Device I/O library that is portable across Single Board Computers and microcontrollers. Tested with Raspberry Pi, Odroid C2, BeagleBone Black, Next Thing CHIP, Asus Tinker Board and Arduinos / Pico. Supports GPIO, I2C, SPI as well as Serial communication. Also known to work with Udoo Quad.
https://www.diozero.com
MIT License
263 stars 59 forks source link

I2C read limit #54

Closed michieltjampens closed 3 years ago

michieltjampens commented 4 years ago

Am i doing something wrong or is there a 32 byte limit to the amount of bytes that can be read in a single transfer? Or is this hardware related (running on beaglebone black) because there's no limit mentioned in the docs. I know it's not the chip that stops sending because a logic analyser schows a stop after 32 bytes.

mattjlewis commented 4 years ago

Hi, I'm not aware of any limit.

michieltjampens commented 4 years ago

Hm, then i'm doing something wrong. For now i worked around it by dividing read instructions, but gues i'll have to look if the beaglebone restricts this somehow.

mattjlewis commented 4 years ago

I'm not ruling out any issues with my library btw, just not sure if I've tested reads > 32 bytes. Let me know if there is anything to fix. Are you using the built-in provider or bbbiolib? Can you test with both?

michieltjampens commented 4 years ago

Using the built-in provider, bbbiolib kept complaining about pwm so i would first need to fix that issue. But given that SPI and all the other I2C stuff works with the built-in this wasn't a priority to look into.

I discovered the limit when trying to interface with a AT24C02D and checked the bus with a Saleae datalogger to be sure it's not on the AT's end.

mattjlewis commented 3 years ago

Ok, I managed to get time to look into this. diozero mainly uses the SMBus interface for I2C transactions. This imposes a 32-byte limit on I2C reads and writes. I've recently updated my Javadoc in my I2CSMBusInterface to make this clear. As you'll see in the Linux Kernel documentation, there are two additional methods that do not have this constraint - i2c_smbus_read_i2c_block_data() and i2c_smbus_write_i2c_block_data(). I have replicated these methods within diozero as well as two of my own extension methods. I am also prototyping a "raw" I2C read-write interface, here is the relevant interface https://github.com/mattjlewis/diozero/blob/master/diozero-core/src/main/java/com/diozero/api/I2CDeviceInterface.java#L43.

michieltjampens commented 3 years ago

Thanks, i'll look into those when i'm working with i2c memory again.

Fyi i'm using Diozero to handle the i2c (and spi but not that extensive yet) communication for a datalogger. The datalogger itself is obviously written in java but all i2c communication is setup in xml (so pretty much script to java).