SPRUIM2H May 2020 – October 2023 AM2431 , AM2432 , AM2434 , AM6411 , AM6412 , AM6421 , AM6422 , AM6441 , AM6442
An Rx channel teardown is intended to be initiated at the data source (the source thread). Initiation is commanded by the host by writing the teardown bit in the PSI-L source thread register DMASS0_BCDMA_0_RCHANRT_ctl_j. This will cause the source of the data to gracefully terminate any packet that is in flight and send a PSI-L data phase with the tdown signal asserted. When the BCDMA receives a data phase with the tdown attribute asserted it will immediately set the internal rx_teardown bit in the Rx Channel N Realtime Control Register (<RCHANRT[a]_RRT_CTL > [30] RX_TEARDOWN).
Upon seeing the rx_teardown bit asserted the port can perform either a graceful (no data loss) or forced teardown of the channel depending on the setting of the rx_forced_teardown bit in the Rx Channel N Realtime Control Register (<RCHANRT[a]_RRT_CTL > [28] RX_FORCED_TEARDOWN).
If the rx_forced_teardown bit is clear, a normal teardown has been initiated. In this case, the BCDMA will do the following:
Stops performing any additional prefetches for the channel (TR mode channels)
Completes any packets normally which may be pending in the ingress port buffers (what the port considers as pending packets is application specific).
Clears the channel enable in the Rx Channel Global Configuration Register (<RCHANRT[a]_RRT_CTL > [31] RX_ENABLE).
Resets the channel state (including scoreboards, FIFOs, counters, statistics, etc.) to their after reset values.
Sets bit 31 of the Rx Flow Reverse Ring Occupancy register (<RINGRT[a]_RT_ROCC> [31] TDOWN_COMPLETE) to indicate that a teardown has completed.
If the current Rx reverse ring occupancy is 0, issues an Rx reverse ring completion up event which is then routed to an IA and can be further routed to any event consumer.
If the current RX Reverse ring occupancy is not 0 then a write to the doorbell with a negative value of the current occupancy will clear any remaining work but the forward ring pointer will remain the same. If the ring pointer needs to be reset then perform a write to any of the ring configuration registers.
If the rx_forced_teardown bit is set, a destructive teardown has been initiated. In this case, the BCDMA will do the following:
Suspends any triggers to allow the channel to operate even if the trigger source is no longer functioning.
Completes any packets which may be pending in the ingress port buffers with or without transferring any data or generating events (the implementation has the option of doing whichever is simplest for that implementation) . Packets will be drained from the Rx FIFO either using ‘null’ write transfers or real transfers and the Packet Descriptors will be returned with an accurate accounting of actual bytes transferred.
Clears the channel enable in the Rx Channel Global Configuration Register (<RCHANRT[a]_RRT_CTL > [31] RX_ENABLE).
Resets the channel state (including scoreboards, FIFOs, counters, statistics, etc.) to their after reset values.
Sets bit 31 of the Rx Flow Reverse Ring Occupancy register (<RINGRT[a]_RT_ROCC> [31] TDOWN_COMPLETE) to indicate that a teardown has completed.
If the current Rx reverse ring occupancy is 0, issues an Rx reverse ring completion up event which is then routed to an IA and can be further routed to any event consumer.
The host may issue a teardown on any channel at any time, regardless of whether the channel is actively receiving a packet or not. The normally intended method of issuing a teardown on a packet mode channel is to initiate the teardown at the remote PSI-L data source and allow it to flow into the BCDMA. If that is not possible, the host may write the rx_teardown bit directly to a 1.
The Host determines that a teardown using either of the following methods:
Periodically polling the teardown and enable bits for the channel
Waiting for an interrupt and observing the teardown complete bit is set in the channel’s default flow (first flow in channel) reverse occupancy register (<RINGRT[a]_RT_ROCC> [31] TDOWN_COMPLETE) for the channel.