Re: Two last bytes missed in callback function (stream data)

["E.S. Rosenberg" <es.rosenberg+libftdi.i2net@xxxxxxxxx>]

Have you tried what the kernel-driver 'sees'? (ie. /dev/ttyUSBX instead of libftdi)

HTH,

Eli

2015-04-11 3:23 GMT+03:00 Julio Cruz Barroso <julio.cruz@xxxxxxxxxxxxxx>:

Ryan,

The answers at the same order:

- No show up at the start of the next transfer. They are missing completely when the package size is 512 (including the status)

- All the package have the status bytes: 0x32 0x60.

- linFTDI filter the status bytes correctly.

Thanks

Julio

On Apr 10, 2015, at 11:05 PM, Ryan Tennill <rtennill@xxxxxxxxxxxxxxxx> wrote:

Do the missing bytes show up at the start of the next transfer or are they completely missing? There are status bytes sent by some/most/all? the chips that would eat into the available payload space. I don't remember if libFTDI filters these bytes out or not.

ref: http://www.ftdichip.com/Support/Knowledgebase/index.html?an232b_04smalldataend.htm
ref: https://code.google.com/p/usb-serial-for-android/issues/detail?id=4

Ryan

On 04/10/2015 06:26 AM, Julio Cruz Barroso wrote:

Hi All,

 

I try to run the same testing in Windows using FTDI libraries in D2XX mode.

 

The results are similar in synchronous mode, every 510 bytes, data is missing.

 

-          At 4B/s there is no data missing.

-          At 4000B/s start missing 2 bytes every 510 bytes

-          At 5MB/s is missing 2 bytes every 510 bytes

 

The attached file show the FT2232H signals during every transmission (at 4B/s, 4000B/s and 5MB/s) and the source code including the initialization and read loop.

 

It seems that was not a problem in PC (libusb, libftdi, d2xx).

 

Has anyone had the same experience?

 

Regards

 

Julio

 

 

From: Julio Cruz Barroso
Sent: Friday, April 10, 2015 9:38 AM
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Subject: RE: Two last bytes missed in callback function (stream data)

 

Hi all,

 

In my previous email, I switched (my mistake in the text) synchronous and asynchronous mode!. In fact, the system is working in asynchronous mode (10MB/s) and is missing two bytes in synchronous mode.

 

Julio

 

From: Julio Cruz Barroso
Sent: Thursday, April 09, 2015 10:21 PM
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Subject: Two last bytes missed in callback function (stream data)

 

Dears,

 

Currently, I have a system running a FTDI in synchronous mode. It contain a FPGA sending data to the PC using a FT2232H (please, refer to diagram below).

 

Basically, the speed is controlled by a signal generator connected to an input of the FPGA. In this case, the throughput could be change easily for testing purposes.

 

The maximum transmission speed is around 10MB/s in this synchronous mode. However, in asynchronous mode there is data missing as explain below using three (3) different speeds (please, refer to next 3 figures):

 

1.       The figure 1 shows the data received in the callback function. In this case, the size is 4 bytes. No data is missing.

2.       The figure 2 shows a higher speed. In this case, the data size in the callback function is 40 bytes. No data is missing.

3.       The figure 3 shows another speed with a buffer size of 510 byte. After this speed, all the size buffer are the same (510 bytes) and there is always two bytes missing (in the end of the buffer).

 

I tried changing the number of transfers and size without success.

 

Any suggestions?

 

Thanks

 

Julio

 

 

 

 

 

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