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Memo

STUDY THIS!!

CHANGES

OpenWrt version is now v18.06.5. Need to re-assess points of interest.

Terminologies

Need to mark potentially useful terms!

IEEE 802.11 Standards Dictionary

• WOW := Wake On WLAN
• (*)chanctx := channel context
  • struct ath_chanctx defined in /ath9k/ath9k.h
• (*)softc := normally refers to driver specific software context
  • struct ath_softc defined in /ath9k/ath9k.h
  • similar to task_struct??
• ieee80211_*
  • struct ieee80211_* : structs about ieee80211 specifications.
  • struct ieee80211_vif : per-interface data (if == interface)
  • http://www.hep.by/gnu/kernel/80211/API-struct-ieee80211-hw.html
• (*)AIFS := Acknowledgement IFS or Arbitrary IFS
• (*)EIFS := Extended IFS
• (*)C-MPDU := Coded MAC Protocol Data Unit
• (*)A-MPDU := Aggregate MAC Protocol Data Unit
• (*)S-MPDU := Single MAC Protocol Data Unit
• CCA := Clear Channel Assessment or Carrier-Controlled Approach
• TX/RX := Abbreviations for Transmit/Receive
• ACS := Adaptive Channel Selection
  • AC := Access Control ?
• (*)RIFS := Reduced IFS
• DMA := Direct Memory Access
• HAL := Hardware Abstraction Layer
  • Seems like manufacturers hide their lower level implementations in the form of HAL as binary code.

Brain-fficial Stuff

• vifs/nvifs means virtual interfaces, non-virtual interfaces
• static int ath9k_conf_tx is "configure transmission queue" function

Points of Interest

/ath9k/main.c

• struct ieee80211_ops ath9k_ops = { ... };
  • line 2631
  • This is an interface to which other code can invoke callbacks. (recall WRR scheduler!)
• static int ath9k_conf_tx( ... )
  • line 1621
  • possibly used for configuring (or updating) transmission queue

/ath9k/mac.c

managing transmit & receive actions

/ath9k/mac.h

• OFDM_SIFS_TIME and INIT_AIFS
  • line 44, 59

/ath9k/hw.c

writes parameters such as sifs to hardware (register)

• void ...init_global_settings (...)
  • line 1026
  • calculate & set sifs time, slottime, ack timeout, cts timeout

/ath9k/init.c

driver initialization

• static int ath9k_init_queues ( ... )
  • line 344
  • calls ath_txq_setup(...)

/ath9k/xmit.c

• struct ath_txq *ath_txq_setup ( ... )
  • line 1701~
  • qi.tqi_aifs = ATH9K_TXQ_USEDEFAULT ?

/ath9k/ath9k.h

• struct ath_txq
  • line 159
  • transmission queue struct

Points of NON-Interest

• /ath9k/reg.h
• ~~_phy.c/h
• beacon.c
• ~~_wow.c/h
• dynack.c
• htc_~~.c/h
  • htc driver is related to USB

Need to Investigate

Seems like driver is built around generic files such as mac.c, hw.c and then adds device/chipset specific code like arXXXX_~~.c/h. Therefore, have to pinpoint which chipset/cpu we're dealing with.