Fujitsu MB90335 Series Hardware Manual page 259

CHAPTER 11 USB FUNCTION
11.4 Operation Explanation of USB Function
●
IN direction (host PC → device) forwarding
Host PC
Device
Device
DRQ flag *
Host PC
CPU clear
DMAE
DRQIE
DRQ
DER(Enx)
DMA sending buffer write
(DATA0)
In IN- direction transfer, a USB device must perform processes in the follows steps:
1. When the DRQ flag is set and enters the interrupt process, it sets the number of pieces of data to be
transferred in an IN packet in the data counter register DDCT of DMA, enables DMA with the DER
register, and start transfer.
2. Once DMA transfer has been completed, it clears the corresponding DRQ flag in the EP1S to EP5S
registers and the corresponding interrupt factor flag in the DSR register of μDMAC and returns from the
interrupt process.
*: EP1 to EP5 consists of the double buffers, it can be cleared only when one buffer that is not being
accessed has already data written into it and data is written into another buffer that is being accessed
and cannot be cleared even though "0" is written to it when one buffer that is not being accessed is
empty (Dotted line status). It continuously enters the DRQ interrupt process.
238
Figure 11.4-16 IN Packet Forwarding
IN packet
IN ACK
DRQ flag *
DATA0
CPU clear
DMA sending buffer write
(DATA1)
FUJITSU MICROELECTRONICS LIMITED
MB90335 Series
IN packet
IN ACK
DATA1
CM44-10137-6E