doc/tbf.txt: Update and improve some information
Change-Id: I3cd643ef462637708c69895c62c488554a428571
diff --git a/doc/tbf.txt b/doc/tbf.txt
index 9d0db1a..f5b39c5 100644
--- a/doc/tbf.txt
+++ b/doc/tbf.txt
@@ -117,13 +117,17 @@
Polling:
In order to poll uplink control block from MS, a special poll state and
- frame number is stored at TBF. The scheduler reads that value and will not
- assign uplink resource for other TBFs at that frame number.
+ frame number is stored at PDCH UL Controller. The scheduler reads that value
+ and will not assign uplink resource for other TBFs at that frame number.
- When there is no uplink transmission received on the block, a timeout is
- indicated by layer 1 interface. There are two ways of checking timeout:
- - The received frame is bad (BFI).
- - The GSM indicates that the block should have been already received.
+ On receipt of an Uplink RLCMAC block, it's the duty of each specific message
+ handler to release the expectancies previously stored in the PDCH UL
+ Controller. After the specific handler returns, the generic return path will
+ expire all reserved events up to the curent FN for that PDCH, eventually
+ calling timeout functions on TBFs and SBAs owning those reservations. Hence,
+ the layer 1 interface is expected to provide DATA.ind for each FN block,
+ containing data=0 if decoding failed, in order to keep the clock up-to-date in
+ upper layers.
Because polling requires uplink response from MS, the polling must be
performed at control TS.
@@ -131,13 +135,21 @@
Data structures of TBFs and PDCHs:
- There is a global structure for BTS.
+ There is a global structure for PCU (struct gprs_pcu the_pcu).
- The BTS structure has 8 TRX structures.
+ A BTS is created and put into PCU's list for each PCUIF INFO_IND with a unique
+ bts_nr received.
+
+ Each BTS structure has 8 TRX structures.
Each TRX structure has 8 PDCH structures, one for each timeslot.
- There are two linked lists of TBF instances:
+ Each BTS structure has a list of MS (struct GprsMs).
+
+ Each MS can have 1 UL TBF and 1 DL TBF, and 1 TBF is always assigned to an
+ existing GprsMS structure.
+
+ Each BTS also has two linked lists of TBF instances:
- uplink TBFs
- downlink TBFs
@@ -158,4 +170,6 @@
On release of a TBF, the link to this PDCH is removed from all assigned
PDCHs. The TBF is removed from the list of TBFs. The TBF is destroyed.
-
+ GprsMs structures are kept alive for a while once they become unused, in order to
+ have a cache of MS related information it would otherwise need to acquire
+ again once it interacts with the PCU again.