doc/tbf.txt: Update and improve some information
Change-Id: I3cd643ef462637708c69895c62c488554a428571
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doc/tbf.txt
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doc/tbf.txt
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@ -117,13 +117,17 @@ Control TS:
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Polling:
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In order to poll uplink control block from MS, a special poll state and
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frame number is stored at TBF. The scheduler reads that value and will not
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assign uplink resource for other TBFs at that frame number.
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frame number is stored at PDCH UL Controller. The scheduler reads that value
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and will not assign uplink resource for other TBFs at that frame number.
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When there is no uplink transmission received on the block, a timeout is
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indicated by layer 1 interface. There are two ways of checking timeout:
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- The received frame is bad (BFI).
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- The GSM indicates that the block should have been already received.
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On receipt of an Uplink RLCMAC block, it's the duty of each specific message
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handler to release the expectancies previously stored in the PDCH UL
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Controller. After the specific handler returns, the generic return path will
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expire all reserved events up to the curent FN for that PDCH, eventually
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calling timeout functions on TBFs and SBAs owning those reservations. Hence,
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the layer 1 interface is expected to provide DATA.ind for each FN block,
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containing data=0 if decoding failed, in order to keep the clock up-to-date in
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upper layers.
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Because polling requires uplink response from MS, the polling must be
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performed at control TS.
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@ -131,13 +135,21 @@ Polling:
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Data structures of TBFs and PDCHs:
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There is a global structure for BTS.
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There is a global structure for PCU (struct gprs_pcu the_pcu).
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The BTS structure has 8 TRX structures.
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A BTS is created and put into PCU's list for each PCUIF INFO_IND with a unique
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bts_nr received.
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Each BTS structure has 8 TRX structures.
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Each TRX structure has 8 PDCH structures, one for each timeslot.
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There are two linked lists of TBF instances:
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Each BTS structure has a list of MS (struct GprsMs).
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Each MS can have 1 UL TBF and 1 DL TBF, and 1 TBF is always assigned to an
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existing GprsMS structure.
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Each BTS also has two linked lists of TBF instances:
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- uplink TBFs
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- downlink TBFs
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@ -158,4 +170,6 @@ Data structures of TBFs and PDCHs:
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On release of a TBF, the link to this PDCH is removed from all assigned
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PDCHs. The TBF is removed from the list of TBFs. The TBF is destroyed.
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GprsMs structures are kept alive for a while once they become unused, in order to
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have a cache of MS related information it would otherwise need to acquire
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again once it interacts with the PCU again.
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