SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP
Host— The host is an intelligent system resource that configures and manages each communications control module. The host is responsible for allocating memory, initializing all data structures, and responding to port interrupts.
Channel— A channel refers to the sub-division of information (flows) that is transported across a DMA engine. Each channel has associated state information. Channels are used to segregate information flows based on the protocol used, scheduling requirements (for example, CBR, VBR, ABR), or concurrency requirements (that is, blocking avoidance). Information flow within a channel is a stream of strongly ordered information.
Data Buffer— A data buffer is a single data structure that contains payload information for transmission to or reception from a channel.
Buffer Descriptor— A buffer descriptor is a single data structure that contains information about one or more data buffers.
Packet Descriptor— A packet descriptor is another name for the first buffer descriptor within a packet. Some fields within a data buffer descriptor are only valid when it is a packet descriptor including the tags, packet length, packet type, and flags. All Monolithic type descriptors are packet descriptors (and are also a Data Buffer).
Queue— A queue is a list of strongly ordered entries which is typically used to pass work between a producer and a consumer. Queue entries in most cases are references to a work payload which is being passed, but in some cases, (Transfer Request Packets for example) queue entries may actually contain data which is being transferred. Queues are used throughout DMA whenever communication is required between entities. Queues can have multiple different implementations and DMA uses two of the most common: linked lists and rings.
Linked list— A linked list is a data structure in which each entry stores not only the entry data but also a chaining pointer to the next entry in the list. The last entry in each list has its chaining pointer set to NULL (typically encoded as 0x0). The list manager maintains a pointer to the head element on the list and to the tail element on the list. Since the chaining pointer is stored with the entry data, linked lists have a length which is dynamically changeable and limited only by the ability to allocate additional entries which are to be queued/de-queued. Linked lists are present in Host Descriptors to chain multiple descriptors to form a packet.
Ring— A ring is a data structure in which a contiguous memory block defined by M N-byte entries (total size is M × N bytes) is statically allocated and sequentially written/read in order to pass data or data references. Rings are also referred to as circular buffers because when the last element in the contiguous memory array is written, the pointers wrap back to the beginning address for the ring and start the process all over again. The Ring Accelerator component uses rings in order to implement logical queues.
Free Descriptor/Buffer Queue— A free descriptor/buffer queue is a list of available descriptors with prelinked empty buffers that are to be used by the receive ports for host type descriptors. Free Descriptor/Buffer Queues are implemented by the Ring Accelerator.
Free Descriptor Queue— A free descriptor queue is a list of available descriptors that are not yet linked with buffers that are to be used by the receive ports for monolithic type descriptors. Free Descriptor Queues are implemented by the Ring Accelerator.
Packet Queue— A packet queue is a list of valid (that is, populated) packet descriptors that is used for forwarding a packet from one entity to another for any number of purposes. Packet Queues are implemented by the Ring Accelerator.
Memory— Memory is an area of data storage managed by the host. This area is visible to the port as a 64-bit addressable area.
Device Driver— A device driver is application independent software that runs on the host for purposes abstracting the low level hardware so that upper level software can use the hardware without knowing every bit field location or initialization sequence. General device driver functions include port initialization, transmit packet queuing, and receive packet processing.
SOP— Start of Packet. This refers to the descriptor/buffer that is the first buffer in a packet.
MOP— Middle of Packet. This refers to the descriptors/buffers that are neither the first or last buffers in a packet.
EOP— End of Packet. This refers to the descriptor/buffer that is the last buffer in a packet.