FT232H, asynchronous fifo, read error -8 when long byte sequence is supposed to be received

[kormi@xxxxxxx]

Hi,

 

I am using the asynchrounous 245 fifo mode on a FT232H. I used the Windows program FT_Prog to enable this mode on the eeprom. According to the datasheet, without further setting of the bit_mode the chip is now in this asynchronous mode. I see with the HTerm program that data is sent and received accordingly.

 

The system is intended to work with a Linux ARM board with the C++ wrapper of libftdi. I use version 1.4. Data is received and sent correctly, unless a large sequence of data is supposed to received by the software, i.e. the hardware sends e.g. 1000 bytes while respecting the TXEn line. This package size is set on the hardware side, not in the software.

The problem is, that I get an error on the read function when the package size exceeds 1500 bytes. Below this, it works fine. I played with the read_chunk_size without any effect. Disturbing is, that HTerm receives all data accordingly, even with very large byte sequences.

 

This is the relevant code:

 

fStatus=fFD.open(vid,pid,it->description(),it->serial());
cout << "opened with " << fStatus << endl;

//0 -> okay

fStatus=fFD.reset();

//0-> okay

 fStatus = fFD.set_flow_control( SIO_RTS_CTS_HS);
//needed?? 0-> okay

fStatus = fFD.set_latency(16);
//Crash with 2, 16 okay. Is this something to play with?

fFD.set_usb_read_timeout(1500);
fFD.set_write_chunk_size(1);

//only single characters are written to the device, then it is supposed to respond. Works if set to 1.
fFD.set_read_chunk_size(1000);

//played with this one. Does not seem to change much. I even removed this line, the error still happens.

uint8_t buf[1];
buf[0] = 0x7F;
fStatus = fFD.write( buf, 1);

//special character sent to device. Now it starts sending a large package of bytes. The TXEn line is respected by the other end

uint8_t* buffer = new uint8_t[2*gl];
int bytes=0;
int increment=0;
while(bytes<2*gl) {
                increment=fFD.read(&buffer[bytes], 2*gl-bytes);

                //here I receive: -8

                //it has been tried to just read some bytes at once, with the same effect. The only thing that matters is the number of bytes the hardware sends upon receiving the 0x7F character.
                if(increment<0) {
                      cout << "reading error: " << increment << endl;
                }
                bytes+=increment;
}

 

I would be very happy if anyone can give me a hint what is going wrong, i.e. how to interpret the -8 error code and what to change to get this working (and why this works in HTerm?)

 

I would change to the kernel serial driver, however, it is intended to switch from asynchronous to synchronous fifo mode in the future. Therefore I would like to stay with libftdi.

 

Thank you very much for your help and hints!

 

Thomas

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