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Topics - a4711

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Discussion - Drivers / Relinkable object files for libft4222
« on: November 23, 2021, 10:15:08 PM »
Since libft4222 links to ftd2xx which links statically to libusb (L-GPL), I would like to link libft4222 to different version of libusb. I am kindly requesting access to relinkable object files for libft4222 similar to how you distribute ftd2xx.

Thanks.

2
Discussion - Drivers / FT4222: Very high CPU load and gaps between bytes
« on: November 06, 2021, 06:41:40 AM »
We are using a FT4222 with libFT4222 1.4.4.44 to communicate to an I2C peripheral at 400 KHz. Our communication involves a mix of writes and reads, but mainly we are reading out chunks of 128-256 bytes. We are facing two problems:
  • The CPU load caused by libft4222 is extremely high. On a Raspberry Pi Zero this is becoming a bottleneck.
  • There a gaps between bytes on all platforms.

Here you can see the gaps:

As you can see, there is no gap between address byte and the first data byte, but every subsequent byte. On a modern x86 processor and Windows the gaps are at least 8µs long, on a Raspberry PI3 and Linux they are 17µs large. One byte takes about 23µs which means we are wasting 40% of our bandwidth. On a FT232H we don't see these kind of gaps and the CPU load is much better.

We are using the FT4222_I2CMaster_Read() function as shown in the example, nothing else.

  • How can we avoid having such gaps in the transfer?
  • How can we achieve a lower CPU load?

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