SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP
Packet transmission in TR Packet mode involves the following steps:
The Host allocates and populates a type 15 TR packet descriptor. The host will initialize the following fields within the packet descriptor:
Descriptor Type (set to TR)
Reload Enable to 1 if looping is required, otherwise 0
Reload Index to an appropriate offset if Reload Enable set, otherwise 0
Last Entry to TR count minus 1
TR Nominal Element Size to a value that is as large as required for any given TR in the buffer
A set of one or more valid Transfer Request records whose quantity matches the last index specified previously.
The Host queues the packet onto one of the Block Copy Queues for the desired BCDMA channel. Channels may provide more than one Queue (1 queue per provided flow) and may provide a particular prioritization policy between the queues. This behavior is application specific and is controlled by the DMA controller/scheduler implementation.
The BCDMA internally provides a level sensitive status signal for the queue which indicates if any work is currently pending. This level sensitive status line is sent to the hardware block which is responsible for scheduling DMA operations.
The DMA controller is eventually brought into context for the corresponding read channel and begins to process the packet.
The DMA controller reads the packet descriptor pointer from the ring in memory.
The DMA controller reads the packet descriptor from memory
The DMA controller sequentially empties the data region in the descriptor by reading the contents in one or more nominal TR sized block data moves. As a TR is read from the descriptor, it is stored in the internal state of the DMA channel until it is completed.
All of the data transfers specified in a TR will be completed as a series of reads followed later on by a set of corresponding writes (which may or may not be the same size based on the parameters in the block copy TR).
The BCDMA will wait until write status returns for the final write operation that was initiated for each TR. When the final write status is returned within each TR, the BCDMA will write the response into the TR buffer in the Transfer Response records array. Each response is written into an array index which directly matches the index of the request record to which is corresponds.
When all Transfer Requests in the packet have been processed and all Transfer Responses have been written back and confirmed to have landed in memory, the BCDMA will increment the reverse occupancy for the channel/flow.
After the occupancy is incremented, the BCDMA will indicate the status of the Tx Completion Queue by sending an up event.
The Interrupt Aggregator receives the up event and sets the corresponding bit in the interrupt status register (VINT[a]_STATUS_SET) as programmed in the interrupt mapping registers. This in turn causes an interrupt to the Host to be generated.
The Host responds to the status change from the BCDMA (via the Interrupt Aggregator) and performs garbage collection as necessary for the packet.
During garbage collection the Host will write to the reverse queue Doorbell register (RINGRT[a]_RT_RDB) for the channel/flow to acknowledge the popping of those completed packets. The doorbell writes eventually cause the queue to become empty.
The BCDMA will send a down event to the Interrupt Aggregator which will clear the corresponding bit in the Interrupt Status Register (VINT[a]_STATUS) and potentially de-assert the interrupt line