Atheros Communications, Inc. AR9223 Single-Chip 2x2 MIMO MAC/BB/Radio for 802.11n WLANs • 19
COMPANY CONFIDENTIAL October 2009 • 19
The Tx descriptor format for words 2 through
13 is described in Table 3-2.
Table 3-2. Tx Control Descriptor Format (Words 2–13)
Word Bits Field Name Description
2 11:0 frame_length Frame length
Specifies the length, in bytes, of the entire MAC frame, including the frame
check sequence (FCS), initialization vector (IV), and integrity check value
(ICV) fields.
12 vmf Virtual more fragment
If this bit is set, bursting is enabled for this frame. If no burst is in progress, it
initiates a CTS-protected burst if cts_enable is set. If a previous burst is in
progress, it ignores the cts_enable bit and assumes the burst is protected.
13 RES Reserved
14 low_rx_chain When set to 1, indicates that the Rx chain mask switches to low power mode
after transmitting this frame.
15 clear_retry Setting this bit disables the retry bit from being set in the Tx header on a
frame retry (applies to both aggregate and non-aggregate frames).
21:16 tpc_0 Tx power control for series 0
These bits pass unchanged to the baseband, where they are used to control
the transmit power for the frame.
22 rts_enable Request to send (RTS) enable. At most, one of the “rts_enable” and
“cts_enable” bits may be set; it is illegal to set both.
set PCU transmits the frame using the RTS/CTS protocol
clear PCU transmits the frame using the contention/backoff protocol
23 veol Virtual end-of-list flag
When set, indicates that the QCU should act as though the descriptor had a
NULL LinkPtr, even if the LinkPtr is not NULL. Must be valid in the final
descriptor of a frame and must be clear for all other descriptors of the frame.
24 clear_dest_mask Clear destination mask bit flag
If set, instructs the PCU and DCU to clear the destination mask bit at the
index specified by the DestIdx field.
28:25 RES Reserved
29 int_req Interrupt request flag
Set to one by the driver to request that the DMA engine generate an interrupt
upon completion of the frame to which this descriptor belongs.
Note that this field must be valid and identical for all descriptors of the
frame; that is, all descriptors for the frame must have this flag set, or all
descriptors for the frame must have this flag clear.
30 dest_index_valid Destination index valid flag
Specifies whether the contents of the DestIdx field are valid.
31 cts_enable Proceed frame with CTS flag
If set, the PCU first sends a CTS before sending the frame described by the
descriptor. Used for 802.11g and Atheros XR frames to quiet legacy stations
before sending a frame the legacy stations cannot interpret (even at the PHY
level). At most, one of the “rts_enable” and “cts_enable” bits may be set; it is
illegal to set both bits.
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