It also add two configurations for the USB device even loop thread:

    RT_USBD_THREAD_STACK_SZ to set the stack size, default to 2048
    RT_USBD_THREAD_PRIO     to set the priority, default to 8

You can overwrite the default values in rtconfig.h

serial: use RT_SERIAL_RB_BUFSZ to define the size of ring buffer.

Fix usb serial

We start the sending transaction in SOF handler. But if the data is
already sending, start an other transaction will cause data lose.
Implement a state machine is cdc_vcom and avoid that.

Sort the switch cases by the frequency of the events.

The data filled into dcd_ep_write does not to be limited by
MaxPacketSize.

This commit set the buffer for packet to CDC_MaxPacketSize which is a
reasonable value for it. However, maybe we should make
CDC_{RX,TX}_BUFSIZE configurable as well.

Ringbuffer

The new implementation use the mirroring method to distinguish full
buffer and the empty buffer. It also support buffers of arbitrary size.

usbdevice/core/core.c: fix garbage value bug

This could crash the program with -O1 and -O2 in MDK.

1.1.0 -> 1.2.0

1.1.0 -> 1.2.0

2006 - 2013 Copyright by rt-thread team

error: expected expression before 'void'
error: too many arguments to function

Use SRAM as EMAC transmit buffer, to avoid the underrun error, especiall...

Use SRAM as EMAC transmit buffer, to avoid the underrun error, especially in the large amount of data communication.

Dfs clean and optimized code

strip more characters in finsh token.

fix spelling error by ziyi897, this commit fixes #74.