NEC Network Controller uPD98502 - Manual (Page 341)

CHAPTER 6 USB CONTROLLER
Preliminary User’s Manual S15543EJ1V0UM 341
6.5.5 USB controller processing at data transmitting
This section presents all of the processing performed by USB Controller at data transmitting.
Figure 6-10. USB Controller Transmit Operation Flow Chart
T x co m m and is set
C op ies the com m and to internal
register,and clears U S B C om m a nd
R egister B usy bit
R est area of T x FIFO
≥
B uffer size
Y es
N o
N o
T ransfers to U S B
U pd ates w rite p ointer of T x
m ailbox.
S ets T x E nd b it in U G S R 1
register.
(1)
(5)
(6)
(7)
(9)
(8)
(10 )
(13 )
(3)
S pecified E ndP o in t is
B usy?
Y es
W ait until the E ndP oint
ca n execute T x com m and
R ea ds buffer descriptor
D M A tran sfers from buffer
to FIFO
D M A tran sfer from bu ffer to
FIFO
R ea ds next buffer
descrip tor
Last data ?
Y es
N o
S ends to U S B
W rites T x indication
to m ailbox
(4)
(11 )
(12 )
(14 )
(15 )
S et U S B C om m and R egister
B usy bit to "1".
(2)