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This function indicates to the USB module that the USB device has been attached to the bus. This function needs to be called in order for the device to start to enumerate on the bus. --> 測試usb裝置是否有插入至USB的BUS之中

Should only be called when USB_INTERRUPT is defined.  --> 說明USBDeviceAttach()跟著USB_INTERRUPT使用

For normal USB devices: Make sure that if the module was previously on, that it has been turned off for a long time (ex: 100ms+) before calling this function to re-enable the module. If the device turns off the D+ (for full speed) or D- (for low speed) ~1.5k ohm pull up resistor, and then turns it back on very quickly, common hosts will sometimes reject this event, since no human could ever unplug and reattach a USB device in a microseconds (or nanoseconds) timescale. The host could simply treat this as some kind of glitch and ignore the event altogether.

void USBDeviceTasks();

This function is the main state machine of the USB device side stack. This function should be called periodically to receive and transmit packets through the stack. This function should be called preferably once every 100us during the enumeration process.After the enumeration process this function still needs to be called periodically to respond to various situations on the bus but is more relaxed in its time requirements. This function should also be called at least as fast as the OUT data expected from the PC.  --> 需要週期性地call USBDeviceTasks()來傳遞或接受Packets,  週期最好是100us, 至少要跟pc端OUT的資料一樣快

Typical usage:

void main(void)
{
    USBDeviceInit()  --> 需要在USBDeviceTasks()之前
    while(1)
    {
        USBDeviceTasks();
        if((USBGetDeviceState() < CONFIGURED_STATE) ||
           (USBIsDeviceSuspended() == TRUE))
        {
            //Either the device is not configured or we are suspended
            // so we don't want to do execute any application code
            continue;   //go back to the top of the while loop
        }
        else
        {
            //Otherwise we are free to run user application code.
            UserApplication();
        }
    }
}

None

This function should be called preferably once every 100us during the enumeration process. After the enumeration process this function still needs to be called periodically to respond to various situations on the bus but is more relaxed in its time requirements.

void USBDeviceInit();