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2.3.4.4
Message Passing Software Requirements
SRIO Functional Description
Software performs the following functions for messaging:
RX Operation
•
Assigns Mailbox-to-queue mapping and allowable SourceIDs/mailbox- Queue Mapping
•
Sets up associated buffer descriptor memory – CPPI RAM or L2 RAM
•
Link-lists the buffer descriptors, next_descriptor_pointer
•
Assigns single segment (256-byte payload) and multi-segment (4K-byte payload) buffers to queues
buffer_length
•
Assigns buffer descriptor to data buffer, buffer_pointer
•
Gives control of the buffer to the peripheral, ownership = 1
Configures and initiates RX queues
•
Assigns Head Descriptor Pointer, HDP, for up to 16 queues: RX DMA State HDP
•
Port begins to consume buffers beginning with HDP descriptor and sets ownership = 0 for each buffer
descriptor used. Writes Completion Pointer, CP, RX DMA State CP and moves to next buffer.
•
Port hardware generates pending interrupt when CP is written. Physical interrupt generated when
Interrupt Pacing Count down timer = 0.
Processes interrupt
•
Determines ICSR bit and process corresponding queue until ownership = 1 or eoq = 1
•
Sets processed buffer descriptor ownership = 1
•
Writes CP value of last buffer descriptor processed
•
Port hardware clears ICSR bit only if the CP value written by CPU equals port written value in the RX
DMA State CP register
•
Resets interrupt pacing value
TX Operation
Sets up associated buffer descriptor memory – CPPI RAM or L2 RAM
•
Link-lists the buffer descriptors, next_descriptor_pointer
•
Assigns buffer descriptor to data buffer, buffer_pointer
•
CPU writes buffer descriptors and sets ownership = 1 for each used.
•
Specifies RIO fields: Dest_id, Pri, tt, Mailbox
•
Sets parameters: PortID, Message_length
•
Port starts queue transmit on CPU write to HDP for up to 16 queues - TX DMA State HDP
•
Port processes corresponding queues until ownership = 0 or next_descriptor_pointer = all 0s. Port sets
eoq = 1 and writes all 0s to the HDP.
•
When each packet transmission is complete, the port sets ownership = 0 and issues an interrupt to the
CPU by writing the last processed buffer descriptor address to the CP, TX DMA State CP
Processes interrupt
•
The CPU processes the buffer queue to reclaim buffers. If ownership = 0, the packet has been
transmitted and the buffer is reclaimed.
•
CPU processes the queue until eoq = 1 or ownership = 1
•
CPU
determines
all
packets
have
been
transmitted
if
ownership
=
0,
eoq
=
1,
and
next_descriptor_pointer = all 0s in last processed buffer descriptor
•
CPU acknowledges the interrupt after re-claiming all available buffer descriptors.
•
CPU acknowledges the interrupt by writing the CP value
•
This value is compared against the port written value in the TX DMA State CP register, if equal, the
interrupt is deasserted.
60
Serial RapidIO (SRIO)
SPRUE13A – September 2006
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