2013/1/24 Xiaofan Chen :
> On Thu, Jan 24, 2013 at 10:30 PM, Xiaofan Chen wrote:
>> On Thu, Jan 24, 2013 at 6:27 PM, Wander Lairson Costa
>> wrote:
>>> If you look the code for the Benchmark firmware, you will see that for
>>> OUT bulk and interrupt transfers, the code calls a GetLength function
>>> to know how many bytes it received, but for isochronous transfers, it
>>> always assume it received "packet size" bytes.
>>>
>>
>> I believe this is a simplified design for the isochronous OUT transfer.
>> Technically it may receive less bytes than the wMaxPacketSize
>> of the ISOC OUT Endpoint.
>>
>> This may have something to do with limitation of libusb0.sys'
>> isochronous capability as well. It is not as good as libusbK.sys.
>> libusb-win32 currently only supports fixed user-defined ISOC
>> packet size per transfer.
>>
>
> libusbK does have more advanced ISOC API.
> http://libusbk.sourceforge.net/UsbK3/group__isok.html
>
> Thiis may be more in line with libusbx's isochronous
> API. So in the future, it may be possible to add isochronous
> support to libusbx's Windows backend.
> http://libusbx.sourceforge.net/api-1.0/group__asyncio.html
>
I have been playing with (my modified version) benchmark firmware
regarding this question. After I change it to use the mBDT_GetLength
to get the number of bytes transfered (diff bellow), it now always
transmit only 16 bytes per packet when the number of bytes is 16 or
more:
wander@zeus:isochronous-test (master)$ ./iso-test -n 15
Packet 0 requested to transfer 15 bytes, transfered 15 bytes.
Packet 0 failed to transfer: status = 6.
wander@zeus:isochronous-test (master)$ ./iso-test -n 16
Packet 0 requested to transfer 16 bytes, transfered 16 bytes.
Packet 0 requested to transfer 16 bytes, transfered 16 bytes.
wander@zeus:isochronous-test (master)$ ./iso-test -n 32
Packet 0 requested to transfer 32 bytes, transfered 32 bytes.
Packet 0 requested to transfer 32 bytes, transfered 16 bytes.
wander@zeus:isochronous-test (master)$ ./iso-test -n 20
Packet 0 requested to transfer 20 bytes, transfered 20 bytes.
Packet 0 requested to transfer 20 bytes, transfered 16 bytes.
wander@zeus:isochronous-test (master)$
Despite the fact libusb says it transmitted 32 bytes, mBDT_GetLength
reports that only 16 were actually read.
Diff:
diff --git a/USB_Device_Benchmark/Firmware/Benchmark.c
b/USB_Device_Benchmark/Firmware/Benchmark.c
index fafcbab..8e893c5 100644
--- a/USB_Device_Benchmark/Firmware/Benchmark.c
+++ b/USB_Device_Benchmark/Firmware/Benchmark.c
@@ -544,11 +544,11 @@ void doBenchmarkLoop_INTF0(void)
#endif
break;
case 2:
-#if INTF0_ALT2 == EP_ISO
+/*#if INTF0_ALT2 == EP_ISO
Length = USBGEN_EP_SIZE_INTF0_ALT2;
-#else
+#else*/
Length = mBDT_GetLength(pBdtRxEp1);
-#endif
+//#endif
break;
}
#else
--
Best Regards,
Wander Lairson Costa
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