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?