NFC data transfer too slow using nfcpy

[NFC_code]

Hi guys,
I have written a python application, based on nfcpy, that transfers a binary file onto a type 2 tag.
So far everything worked fine besides the transfer speed. On windows the transfer rate is around 200Bytes/second and on Linux slightly better, 280Bytes/second whereas I would expect a closer values to the theoretical value of 800Bytes/second.
I have stripped completely my python script and my Tag code, so basically I can't blame any of the two applications.
When debugging I do see that the messages take quite a while to write, around 0.8 seconds per record, which is quite a lot. My records have 150 bytes.
So at this point I am inclined to blame the USB driver or the nfcpy which are the only black boxes in this setup.
I have used two different card readers, the Sony S380 and the ACR122, the results on the Sony are slightly better, maybe because it uses a newer version of the PN5XX (PN533) and the ACR122 uses the PN532.
Regarding the drivers I have been using the native drivers, which don't work, and the lisbusb v1.2.6.0, libusbkcv3.0.7.0 which give the above results.
On Linux, the performance increases a bit, to around 250bytes/second, still far from the intended speed.
Does someone have an idea how I can improve the transfer rate on my setup?

my code:

...

if __name__ == '__main__':

...

    msg = None
    with nfc.ContactlessFrontend('usb') as clf:
        print('\nTouch an nfctag containing an ndef message.')
        nfctag = None
        while not nfctag or not nfctag.ndef:
            def onconnect(tag):
                print(tag);
                return False
            def onrelease(tag):
                sys.exit()
            nfctag = clf.connect(rdwr={'on-connect': onconnect, 'on-release': onrelease})
            print(nfctag.ndef.message.type)
            if (packageDebugEnabled):
                printmessage(nfctag.ndef.message)

  ...

        with open(BinaryFile, "rb") as binaryFile:
            while (transfer == TRANSFER_ONGOING):
               ...
                if (readyForNextPackage):
                   ...
                    for chunk in iter(lambda: binaryFile.read(dataChuckSize), b""):
...
                        chunky = list(packageTransferMsgId) + list(CardReaderTag) + list(packagesSizeStringLSB) + list(packagesSizeStringMSB) + list(formattedPackageNumber) + list(chunk) + emptyList

...

                        str1 = ''.join(package)
                        record0 = nfc.ndef.Record(mimeType, '', b'{}'.format(str1))
                        nfctag.ndef.message = nfc.ndef.Message(record0)
   ...
                    if nfctag.ndef.has_changed:
                        message = nfctag.ndef.message
   ....

[Stephen Tiedemann (stephen-tiedemann)]

Can you please measure transfer speed with tagtool.py. For read use "tagtool.py -d nfc.tag --reltime -v" and calculate the data rate from a number of consecutive read ops. Similar for write with "tagtool.py load <binary-ndef-file>".

With an NTAG216 I get about 670 byte/sec for reading and 435 byte/sec for writing.

[Stephen Tiedemann (stephen-tiedemann)]

It is unclear how the issue would be caused by a bug in nfcpy and no further information was provided by the submitter.