FTDI FT232R as USB target - how to set flow control?

I’m trying to write a simple program to interface to an FTDI FT232R chip over USB, using Oleg’s USB Host Shield and leveraging his rev1 host shield software.

Unfortunately I haven’t been able to find anything that feels like a Programming Guide for this particular chip.

I have the USB link up and enumerated, the baud rate set, and now I’m less clear about how to set flow control, namely how to turn it off in the FTDI chip.

From his rev2 host shield software, he makes a call to set flow control as:

pftdi->SetFlowControl(FTDI_SIO_DISABLE_FLOW_CTRL); // defined to be 0x00

which finds a routine in cdcftdi.cpp:

FTDI::SetFlowControl(protocol, xon, xoff) {
pUSB->ctrlReg(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_FLOW_CTRL, xon, xoff, protocol<< 8, 0, 0, NULL, NULL;
}

So I’m assuming that xon = 0; xoff = 0; and protocol<<8 = 0. I’m issuing those to my setup over USB, get a successful return, but then when trying to do a Bulk In transfer, I’m receiving a NAK from the FTDI chip.

Feeding the FTDI’s RX line is another Arduino set to just transmit text over and over again. (When I hook up the FTDI chip to Oleg’s rev2 FTDI loopback app, I’m seeing that data just fine and the RX & TX lights on the FTDI board are flashing, so I believe that my serial “source” is working okay.)

So to distill this down to a specific question, should the zeros in this command properly disable flow control?

result = ctrlXfer( 1, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_FLOW_CTRL, 0, 0, 0, 0, 0x0, NULL);