802.11 Reference Design
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802.11 Reference Design: Frame Rx
When the PHY receives a valid frame it notifies the wlan_mac_dcf_hw core via status signals in the FPGA. The core then notifies the MAC software via status bits in a register.
The lower level MAC software then executes the process illustrated below.
ACK Transmissions via Auto Tx
The wlan_mac_dcf_hw core includes a small state machine which can initiate a PHY transmission in response to a valid PHY reception. This state machine enables transmission of ACK packets fast enough to meet the SIFS timing requirement of the 802.11 DCF.
If the MAC header of an incoming frame indicates an ACK should be transmitted in response, the lower level MAC code prepares an ACK frame in a spare Tx packet buffer. The code then configures the Auto Tx state machine to enable a post-Rx transmission from the ACK buffer if the current reception completes without errors. If the reception finishes with errors the ACK is not transmitted and the Tx packet buffer is recycled. The preparation of the ACK frame occurs while the PHY is still receiving the packet. The lower level MAC software must ensure it completes preparation of the ACK before the reception completes. The Auto Tx state machine will only initiate a transmission if enabled before the last byte of a reception is complete.
