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Texas Instruments TMS320C645X User Manual

Page 55

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SRIO Functional Description

The CPPI module can be powered down if the message passing protocol is not being supported in the
application. For example, if the direct I/O protocol is being used for data transfers, powering down the
CPPI module will save power. In this situation, the buffer descriptor queue SRAMs and mailbox mapper
logic should be powered down. Clocks should be gated to these blocks while in the power down state.

Section 2.3.9

describes this in detail.

2.3.4.5

Message Passing Software Requirements

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 (256B payload) and multi-segment (4KB 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

Gives control of the buffer to the CPU, ownership = 0

CPU writes buffer descriptors beginning with HDP descriptor 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

SPRU976 – March 2006

Serial RapidIO (SRIO)

55

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