L-USS820FD-DB AGERE [Agere Systems], L-USS820FD-DB Datasheet - Page 27

• Manufacturer Part Number: L-USS820FD-DB
• Description: USB Device Controller
• Manufacturer: AGERE [Agere Systems]

Data Sheet, Rev. 1
August 2004
Agere Systems Inc.
Register Interface
Table 26. Transmit FIFO Flag Register (TXFLG)—Address: 04H; Default: 0000 1000B
These flags indicate the status of data packets in the transmit FIFO specified by EPINDEX. This register is
endpoint indexed.
Bit
7:6
TXFIF1
Bit 7
TXFIF[1:0] Transmit FIFO Index Flags (Read Only). These flags indicate which data sets are
Symbol
R
TXFIF0
Bit 6
present in the transmit FIFO (see below).
The TXFIF bits are set in sequence after each write to TXCNT to reflect the addition of a
data set. Likewise, the TXFIF1 and TFIF0 are cleared in sequence after each advance of
the read marker to indicate that the set is effectively discarded. The bit is cleared whether
the read marker is advanced by firmware (setting ADVRM) or automatically by hardware
(ATM = 1). The next-state table for the TXFIF bits is shown below:
In isochronous mode, TXOVF, TXURF, and TXFIF are handled using the following rule:
firmware events cause status change immediately, while USB events cause status change
only at SOF. TXFIF is incremented by firmware and decremented by the USB. Therefore,
writes to TXCNT increment TXFIF immediately. However, a successful USB transaction
any time within a frame decrements TXFIF only at SOF.
The TXFIF flags must be checked before and after writes to the transmit FIFO and TXCNT
for traceability. See the TXFLUSH bit in TXSTAT.
If MCSR.FEAT = 0:
TXFIF[1:0]
TXFIF[1:0]
(continued)
TXFIF bits are immediately visible to the host after a firmware write—the device will
send the indicated data set(s) to the host in response to an IN.
XX
00
01
10
00
01
10
00
01
10
11
11
11
Bit 5
—
—
ds1
Yes
Yes
No
No
Advance Read Marker
Advance Read Marker
Advance Read Marker
Advance Read Marker
Reverse Read Pointer
Bit 4
Write TXCNT
Write TXCNT
Write TXCNT
Write TXCNT
Operation
Data Sets Present
Function/Description
ds0
Yes
Yes
No
No
TXEMP
Bit 3
R
Next TXFIF[1:0]
11 (TXOVF = 1)
Status
Empty
TXFULL
2 sets
1 set
1 set
Unchanged
Bit 2
10/01
01
11
11
00
00
00
USB Device Controller
TXURF
Bit 1
R/W
USS-820FD
TXOVF
Bit 0
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