[Ftdi-usb-sio-devel] 62 bytes... comes from where?

[Kentaro F. <fu...@is...>]

Hello,

We have developed a device employs FT8U232AM and are testing it.
I got some problem with ftdi_sio driver and I need any help.

The device has an FT8U232AM connected to an AVR CPU. When it receives
one byte, then AVR sends 770 bytes data sequentially.
When the baud rate is under 353Kbps (means custom_divisor <= 68),
there is no problem. When the baud rate is up to 700Kbps, or custom_divisor
is 34, it fails to read data from the device file.

We observed following two phenomena.

1) read() call always returns 62 bytes data.
2) when it failed to read, 691 bytes had been read, and read() system-call
   was blocked. After that, we send more one byte, and 691 bytes data returns
   again, so, AVR, FTDI chip and the driver all do not stuck. Rest 79 bytes
   should be lost.

I know those observations are too unclear and it may not be caused by the
ftdi_sio driver. But we need any help or advice.

Our question is

1) why read() returns 62 bytes at once?
2) who drops rest 79 bytes? FTDI or the driver?

We uses the latest driver (version 1.2.1).

Thanks in advance.

Kentaro Fukuchi