Hi Uwe, Thank you for your response!
> We have the FT2232(without H) transmitting CR terminated ASCI data at quite > high rate. One 1Mbyte/sec is ambious, as usable bulk transfer rate is only > http://www.cypress.com/?id=4&rID=29825 > "The maximum you can achieve is about 8.704 Mbits/sec". > The system virtual comm port can be used for read/write, so on a recent PC > side the PC should not be the limiting factor. PC cares for having enough > USB read/write requests pending to keep the UAB and FT busy. What I need is a stream of bytes delivered without hiccups at about 1MB/s. Very much like a sound card. If I were to connect the bytestream to an 8bit DAC, I should be able to generate a low-jitter waveform for as long as the host application keeps sending data. I am currently using an FT232 chip in serial mode going to a PIC. By the time I have a 200kbaud high priority interrupt to unpack the data and manage flow control, a main routine to interpret the (compressed) data, and another interrupt routine to dole it out at precise times, I am limited to about 20kbytes per second throughput. This is for driving stepper pulses in a CNC application, so it is critical that there are no gaps in the byte stream once the application starts to fill the pipeline. > We have the FT2232H transfer block formatted binary data at 15 MByte/s + in > synchronus mode. Async mode will easy go above 1 MByte, as it uses USH High > speed vs full speed on the FT232R. An FPGA on the FT side will also help to > mantain bandwidth. So, my question is whether the FT2232H can produce continuous byte streams on a fixed output clock at 1MByte/sec without requiring an FPGA to do further FIFO storage? I wasn't able to get this kind of operation from an FT245. The resulting byte stream in bitbang mode had horrible stuttering due to random FIFO starvation. > However for both implementation I would refrain to use this setup for time > critical applications with time requirements smaller than one USB microframe > (125 us). At the time of using the FT2232(without H), also a USB 2 hub in > between the FT and the PC helped. Than the PC saw a USB-2 device and used USB > microframes versus normal USB frame (1 millisecond) without the hub. The > situation may have changed however in between. I have no care about latency. I'm only interested that the byte stream not be broken once I start my data dump. I also don't mind up to 10% timing jitter on the bytestream clock, it just can't skip bytes once the pipe is full. I suppose the best way to find out is to build a board and test it. There were some discussions a few years ago where FTDI admitted a bug in the FIFO circuitry on the FT245 and projected that future chips might work better. I am inquiring with the hope that this information might already be known and save me a bit of experimentation. I've search for variants of "FTDI sound card", "FTDI arbitrary waveform generator", and "FTDI synchronous byte stream". If the chip was capable of a smooth unbroken byte stream transfer, it would be tempting to just hang a DAC on the output to make a nice arbitrary waveform generator. There is one old paper that mentions this topology, and it uses the FT245. I think it doesn't really work. When I tried to duplicate the setup, the bytestream had glitches. I'm expecting that I will need to use an FPGA to further buffer the datastream. This is something I haven't done before and would like to avoid if possible. kind regards, -- Rick Walker -- libftdi - see http://www.intra2net.com/en/developer/libftdi for details. To unsubscribe send a mail to [email protected]
