Posted on May 23, 2012 at 09:51Hello.
Please give me some knowledge about the topic.
Now I use STM32F103, and I found 2 strange packets transfer
after initializing endpoint as double-buffered bulk tx.
I found this problem after trying the following steps, 1,2 and 3.
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1.
I initialize endpoint as the following,
almost same as ''AudioSpeaker'' Demo in STM USB-FS LIBRARY.
(but this is not Isochronous)
SetEPType(ENDP1, EP_BULK);
SetEPDoubleBuff(ENDP1);
SetEPDblBuffAddr(ENDP1, ENDP1_BUF0Addr, ENDP1_BUF1Addr);
SetEPDblBuffCount(ENDP1, EP_DBUF_IN, 0x40);
ClearDTOG_TX(ENDP1); // for usb peripheral
ClearDTOG_RX(ENDP1); // SW_BUF for application
ToggleDTOG_RX(ENDP1);
SetEPTxStatus(ENDP1, EP_TX_VALID);
SetEPRxStatus(ENDP1, EP_RX_DIS);
Toggle conditions are also cleared equally
when usb request (Set Configuration, Set Interface, etc.) is received.
2.
I connect a Device to PC via USB analyzer.
3.
I found 3 strange packets when a device starts.
All of them are max-packet-size, first one and second one are different,
but first one and third one are same.
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To improve this strange-packet-transfer, I try to do the following steps, 4 and 5.
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4.
I delete ''ToggleDTOG_RX(ENDP1);'' at any phase to make toggle bit even.
(No Problem to transfer a packet because SW_BUF can be toggled when it is transferred.)
Then I found 2 strange packets when a device starts.
These 2 packets are max-packet-size, first one and second one are different.
5.
I change a packet size from ''0x40'' to ''0x00'' in initialize phase.
(No Problem to transfer a packet because its size can be changed when it is transferred.)
Then I found 2 strange ''NULL'' packets when a device starts.
---
After all, the packets are NULL but I cannot avoid strange-packets-transfer.
Do I have some mistakes or misunderstanding?
#usb-double-buffer
