On Tue, Sep 1, 2020 at 1:19 PM Alexandros adrcki@gmail.com wrote:
The MAX_I2C_BUF_SIZE macro in pii2c.c is set to 64, but still when I try to send 64 bytes to a slave Teensy, only 32 go through, the rest 32 are all 0s. Raising this value to an even greater number, like 128 (which is something I would like to implement), gives similar results. The same behavior occurs whether I set the I2C address as an argument to the object, or if I pass it through the "write" message.
I checked the code and couldn't find where this occurs. I added this:
post("%d", x->x_xferbuf[i-1]);to line 348 to make sure the bytes are stored in the object's buffer, and they do get stored properly. The only place I found they end up in is a "write()" function, called in line 293, inside the pii2c_writer() function. I guess this function is from one of the header files included in the object, as I couldn't find it in the code.
Long story short, is it possible to send more than 32 bytes over I2C in the Pi? I really like [pii2c], and since wiringPi is now deprecated, I'd like to stick to this object.
It seems to be an issue with the kernel driver. Whoever wrote it got it into thieir head that there was a 32-byte limit. I found this discussion: https://stackoverflow.com/questions/25982525/why-i2c-smbus-block-max-is-limi... The same thing happens in Arduino, but there you can edit Wire.h to get bigger messages. I guess it will be fixed eventually. Meanwhile, do you really need to use I2C? SPI is much faster and has no limit to the message size. I also made a [pispi] external... I find in general it's easier to plug an arduino into the pi to do realtime stuff.
Martin
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