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I want to precisely control the time at which packet is transmitted from the
wifi card. For this puprose I have disabled the CCA (using the code provided
here https://systems.cs.colorado.edu/projects/carp). I have tested this
functionality for disabling CCA and it is working fine.
However I have noticed that there is a difference of about 400 microseconds
from the time instant the packet is put in the hardware queue using the
function ath_tx_txqaddbuf, and it's transmission begins. (I have measured
this time difference by labelling the packet as Beacon packet, and then used
the timestamp marked on the beacon pkt to measure this difference). Iam
assuming this 400 microseconds is the time for DMA operation for the packet
to be transferred from CPU to the wifi card, since ath_tx_txqaddbuf in turn
calls ath_hal_txstart which in turn calls ah_startTxDma function.
However I need the functionality by which Iam able to precisely control the
packet transmission time (preferably within few microseconds). Is there a
provision in madwifi for this? For eg. is it possible to transfer the packet
to the wifi card and then control the time at which it gets transmitted??
Any help would be greatly appreciated.