Fujitsu MB90335 Series Hardware Manual page 261

CHAPTER 11 USB FUNCTION
11.4 Operation Explanation of USB Function
Host PC
Device
Device
Host PC
DMAE
DRQIE
DRQ
DER(Enx)
In both OUT- direction and IN- direction transfer, a USB device must perform processes in the following
steps:
1. It sets the total number of pieces of data to be transferred in the data counter register DDCT in DMA
and enables DMA with the DER register.
2. DMAE and DRQIE, are permitting set.
3. Once transfer has been completed, it sets μDMAC again with an interrupt due to the corresponding
interrupt factor in the DSR register of μDMAC and clear the flag if necessary, 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 when one buffer that is not being accessed is empty. It continuously enters the
DRQ interrupt process.
240
Figure 11.4-18 IN Direction (Device → Host PC) Forwarding
IN
DRQ flag *
Automatic
clear
DATA0
Write PKS part of
DMA sending buffer
FUJITSU MICROELECTRONICS LIMITED
Data
ACK
DRQ flag *
DATA0
Automatic
clear
DATA1
Write the rest of
DMA sending buffer
MB90335 Series
Last data
ACK
IN
DATA1
CM44-10137-6E