Anders,
I really would prefer not to have to rebuild the entire Android kernel to solve
this problem. There are all kinds of logistical and technical issues for me if
I have to go that way. For example, it would mean I would need to instruct my
users to reflash their Nexus9 image with my new kernel changes. They would not
be happy to do this. I know the chip can do what I need because I have seen
it work when using the D2XX libraries on other platforms.
I think I may have found something interesting.
Originally, I was only calling these functions (error checking removed for
clarity, but I have it in the code):
ftdiComm = ftdi_new();
ftdiStatus = ftdi_set_interface(ftdiComm, INTERFACE_B);
ftdiStatus = ftdi_usb_open(ftdiComm, VID, PID);
ftdiStatus = ftdi_set_line_property(ftdiComm, BITS_8, STOP_BIT_1, NONE);
ftdiStatus = ftdi_set_baudrate(ftdiComm, baudrate); // baudrate = 921600
ftdiStatus = ftdi_setflowctrl(ftdiComm, SIO_RTS_CTS_HS); // Enable
CTS/RTS hardware flow control
ftdiComm->usb_read_timeout = 1; // 1 millisecond timeout for read
and write. There is no API function to set this, so we just write to the
structure directly
ftdiComm->usb_write_timeout = 1;
ftdiStatus = ftdi_set_latency_timer(ftdiComm, 1); // Set latency
to 1 millisecond, the minimum
The code above never sets the RTS pin low on my logic analyzer.
I was reading some forum on this and it gave me an idea. I added this line
after setting flow control:
ftdiStatus = ftdi_setrts(ftdiComm, 1); // Set RTS low by default
I assumed that using hardware handshake flow control would automatically
control the RTS output based on the receive buffer fullness. Apparently,
that's not totally true. It seems like there is a 'default' state defined by
ftdi_setrts(). I must set that default state to 1 (which makes it come out of
the pin as 0 volts). I tried setting it setting it to 0 at first but found
RTS was always 3.3 volts output, the wrong value for correct flow control.
With this change, I can see RTS goes low at startup. I then write/read many
100 byte chunks and that works with RTS never going high because I always read
the buffer before it fills.
Then, I stop reading and just write 10,000 bytes (some arbitrarily big number
to fill the receive buffer). I see RTS goes high during the transmission.
Woot!!! After writing 10,000 bytes, I read whatever I can from the buffer.
RTS goes low when I start pulling data out of the buffer Woot!! Woot!! :-)
I can read 7,768 bytes from a full receive buffer.
I need to do more testing tomorrow to really make sure all this works like I
expect. I also have to implement the GPIO controls on the other port.
Does my understanding of the need to call ftdi_setrts() make sense? I believed
it would be useless until I did this test.
-dave
-----Original Message-----
From: Anders Larsen [mailto:al@xxxxxxxxxxx]
Sent: Tuesday, August 18, 2015 5:54 PM
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Subject: Re: Help with FT2232H flow control
Hi Dave,
On 2015-08-18 23:29, Dave McMahan wrote:
> Anders,
>
> Thanks for your quick response.
>
> Unfortunately, I can't use only plain serial communications. I must
> use GPIO signals connected to Port A and serial communications on
> Port B.
that alone is not a problem, it's just a bit tricky to set up.
You must "unbind" Port A from the serial driver in order to use the
GPIO pins with libftdi (will check tomorrow @work how I did that and
report back).
> As far as I can tell on Android Lollipop running on a Nexus9 tablet,
> there is no kernel driver for ftdi.
It should not be too difficult to build the ftdi_sio kernel module
since the Google has published the Kernel sources.
http://www.androidpolice.com/2014/11/05/google-releases-kernel-source-for-nexus-9-volantis-and-nexus-player-fugu/
> In any event, I must use libftdi to control the GPIO signals (both
> inputs and outputs) and I thought it would be a bad idea to mix a
> kernel driver with libftdi calls on the same device at the same time.
It is not a problem using separate drivers to handle the separate USB
endpoints of the FT2232H chip - the ports really are independent.
Cheers
Anders
> > From: Anders Larsen [mailto:al@xxxxxxxxxxx]
> > Sent: Tuesday, August 18, 2015 5:22 PM
> > To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
> > Subject: Re: Help with FT2232H flow control
> >
> > Hi,
> >
> > On 2015-08-18 22:01, Dave McMahan wrote:
> > > Hello,
> > >
> > > I am using the FT2232H chip in an Android (linux) environment. I
> am
> > > working with the latest libftdi (version 1.2), libusb (version
> 1.0).
> > >
> >
> > It sounds as if you are using plain serial communications?
> >
> > If so, the FT2232H should Just Work (tm) - the Kernel driver
> ftdi_sio.ko
> > should take care of everything, including hardware flow control
> > (without any special libraries like libftdi or D2XX)
> >
> > Cheers
> > Anders
--
libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
To unsubscribe send a mail to libftdi+unsubscribe@xxxxxxxxxxxxxxxxxxxxxxx
--
libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
To unsubscribe send a mail to libftdi+unsubscribe@xxxxxxxxxxxxxxxxxxxxxxx
|
