STM32_USB-FS-Device_Lib_V4.1.0 : not sure if this is a bug in usb_core.c
STM32_USB-FS-Device_Lib_V4.1.0file :usb_core.cfunciton name:RESULT Standard_ClearFeature(void)code :if (wIndex0 & 0x80){
/* IN endpoint */
if (_GetTxStallStatus(Related_Endpoint ))
{
ClearDTOG_TX(Related_Endpoint);
SetEPTxStatus(Related_Endpoint, EP_TX_VALID);
}
}
else
{
/* OUT endpoint */
if (_GetRxStallStatus(Related_Endpoint))
{
if (Related_Endpoint == ENDP0)
{
/* After clear the STALL, enable the default endpoint receiver */
SetEPRxCount(Related_Endpoint, Device_Property.MaxPacketSize);
_SetEPRxStatus(Related_Endpoint, EP_RX_VALID);
}
else
{
ClearDTOG_RX(Related_Endpoint);
_SetEPRxStatus(Related_Endpoint, EP_RX_VALID);
}
}
}question: i saw that status of IN endpint was set to VALID(EP_TX_VALID) after recover from HALT; i wonder why we don't set the status to NAK; The USB spec doesn't specify how to leave the endpoints after a halt is cleared. but for an interrupt IN endpoint such as a HID device,at that point when the endpoint recover from halt status,the device will send anpacket with uncertain data to the host,since the host automatically query the deviceby IN token in a determined interval constantly,and it can be quite possible for the packet buffer contains uncertain data at that point; possible advice: just set the status to NAK,firmware could set it to VALID if necessary data get ready to transfer to host later.
主要意思是在一个端点从HALT状态恢复后，发送是有效的，那样的话，比如对于一个中断型的IN端点，会自动发给主机一个数据包，这个数据包的内容是不定的，很可能包含未知的数据；疑问就是为何不在端点恢复后将发送端点设置为NAK，在固件准备好数据后在由固件设为VALID。
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