Re: [libusb] Asynchronous transfer using libusb-1.0 on ubuntu

[Chris E <sp...@gm...>]

Serious question; why are you using Libusb to perform low-level file
transfer?  Surely even something like fopen() and fprintf() would be much
easier and safer than low level USB commands.

On 17 Aug. 2017 3:43 am, "Anand Nahar" <and...@gm...> wrote:

> Hi,
>
>
>
> I am trying to transfer a chunk of raw data (say 1 GB) to/from a USB stick
> using libusb-1.0 on Ubuntu. After reading the documentation, I understand
> that the sequence to transfer data is: *command, data and status*.
>
> I am able to read/write raw data to different blocks *synchronously*. The
> code is:
>
>
>
> in loop:
>
>
>
> uint8_t cdb[16]
>
> memset(cdb, 0, sizeof(cdb));
>
> cdb[0] = 0x28;  // Read(10)
>
> cdb[4] = MSB_of_block_to_read_from – Changes in each loop;
>
> cdb[5] = LSB_of_block_to_read_from – Changes in each loop;
>
> cdb[7] = MSB_for_number_of_blocks_to_read;
>
> cdb[8] = LSB_for_number_of_blocks_to_read;
>
>
>
> struct command_block_wrapper cbw;
>
> memset(&cbw, 0, sizeof(cbw));
>
> cbw.dCBWSignature[0] = 'U';
>
> cbw.dCBWSignature[1] = 'S';
>
> cbw.dCBWSignature[2] = 'B';
>
> cbw.dCBWSignature[3] = 'C';
>
> *ret_tag = tag;
>
> cbw.dCBWTag = tag++;
>
> cbw.dCBWDataTransferLength = length_of_actual_data;
>
> cbw.bmCBWFlags = direction;
>
> cbw.bCBWLUN = Logical_unit_number;
>
> // Subclass is 1 or 6 => cdb_len
>
> cbw.bCBWCBLength = cdb_len;
>
> memcpy(cbw.CBWCB, cdb, cdb_len);
>
>
>
> libusb_bulk_transfer(handle, endpoint_out, (unsigned char*)&cbw, 31,
> &size, 1000);    //Command call
>
>
>
> //After all the error handling and successful return of the above control
> call, I actually read the data
>
>
>
> libusb_bulk_transfer(dev, endpoint_in, dataBuffer, length_of_actual_data,
> &size, 5000);    //read data
>
>
>
> //read status, rest of the error handling and data manipulation
>
>
>
> I can read around 15 MB of data in 1 go. I run the above algo in loop and
> read the required amount of data by varying the block numbers.
>
>
>
> Now, I need to do the same thing *asynchronously*. I understand it has 5
> elements:
>
>    1. Allocate transfer
>    2. Fill transfer
>    3. Submit transfer
>    4. Callback function
>    5. Event handler.
>
> I am unable to figure out on how should the asynchronous calls be designed
> so that the command and data calls are made back to back in a loop.
>
> Do I need to submit 2 separate transfers: 1 for command and 1 for data. If
> not, how do I design it?
>
> If we do have to submit 2 transfers, do I need to wait for command call to
> be completed before I can actually read the data? If so, would I be
> achieving significant improvement in the speed?
>
>
>
> Please let me know if you need any more information from my side. Your
> help is truly appreciated!
>
>
> Thanks & Regards
> Anand Nahar
>
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