Subject: Re: [libftdi 0.18] SPI with CBUS Bit-banging FT232H
On Tue, Jul 5, 2011 at 2:31 AM, Alex Stefan
> Thank you very much. I will try it in the morning. From what I saw in the
> Linux kernel, a call to ftdi_set_bitmode has the following 'trace':
> ftdi_set_bitmode -> usb_control_msg -> USB Request Block sent to device.
For those who are following this thread, you may want to refer to
this thread in libusb mailing list.
Basically CBUS bitbang will be slow due to the use of control
transfer and USB 1ms frame (for full speed USB FTDI device)
or 125us USB microframe (for high speed USB FTDI device).
FTDI mentions the following in the AN.
"The FT_SetBitMode and FT_GetBitMode D2XX commands are
required to communicate with CBUS Bit Bang. Since these functions
allow only a single byte to be sent or received, this version of Bit Bang
is much slower than the Asynchronous and Synchronous Bit Bang types
when used to transfer large buffers of data with FT_Write and FT_Read,
but it does provide an additional 4 IO pins for the FT232R. The data
transfer rate is limited by USB frames."
libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
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