Texas Instruments TMS320 DSP - Manual (Page 62)

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6.1 Overview
6.2 Algorithm and Framework
Overview
Rule 6 states that "Algorithms must never directly access any peripheral device. This includes but is not
limited to on-chip DMAs, timers, I/O devices, and cache control registers."
The fact is that some algorithms require some means of moving data in the background of CPU
operations. This is particularly important for algorithms that process and move large blocks of data; for
example, imaging and video algorithms. The DMA is designed for this exact purpose and algorithms need
to gain access to this resource for performance reasons.
The purpose of this chapter is to outline a model to facilitate the use of the DMA resources for
eXpressDSP-compliant algorithms. The support for DMA has been originally introduced to the TMS320
DSP Algorithm Standard through the addition of rules and two standard interfaces: IDMA and ACPY.
Starting with the TMS320 DSP Algorithm Standard Rules and Guidelines, revision SPRU352E, and the
TMS320 DSP Algorithm Standard API Reference, revision SPRU360C, we introduce additional DMA
Rules and Guidelines and new enhanced interfaces, IDMA2 along with ACPY2 for C64x and C5000
devices and IDMA3 for C64x+ devices, which deprecate the original IDMA and ACPY interfaces.
Algorithms that have already been developed using the deprecated IDMA and ACPY APIs remain
eXpressDSP-compliant; however, development of new algorithms should follow the new IDMA2/ACPY2
specification for accessing DMA resources on the C64x and C5000 devices and the IDMA3 specification
for accessing resources from the C64x+ EDMA3 controller.
This chapter references runtime APIs (IDMA2/IDMA3 and ACPY2) that grant algorithms
framework-controlled access to DMA resources. A detailed description of these APIs can be found in the
TMS320 DSP Algorithm Standard API Reference (SPRU360).
This chapter specifies rules and guidelines to facilitate the use of the DMA resources for algorithms. For
an algorithm to utilize the DMA resources, the rules outlined in this chapter must be followed in order to be
considered eXpressDSP-compliant. These guidelines are strongly suggested recommendations.
The algorithm standard looks upon algorithms as pure "data transducers." They are, among other things,
not allowed to perform any operations that can affect scheduling or memory management. All these
operations must be controlled by the framework to ensure easy integration of algorithms, possibly from
different vendors. In general, the framework must be in command of managing the system resources,
including the DMA resource.
Algorithms cannot access the DMA registers directly, nor can they be written to work with a particular
physical DMA channel only. The framework must have the freedom to assign any available channel, and
possibly share DMA channels, when granting an algorithm a DMA resource.
While Rule 6 prevents eXpressDSP-compliant algorithms from directly accessing or controlling the
hardware peripherals, they can access DMA hardware via "logical" DMA channels they request and
receive from the client application using the standard IDMA interfaces. Algorithms submit DMA transfer
requests to a logical channel using the ACPY2 API functions provided by the client application when using
IDMA2 i nterfaces and custom DMA access protocol when using IDMA3 interfaces.
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IDMA2. All algorithms that use the C64x and C5000 DMA resources must implement the IDMA2
interface. This interface allows the algorithm to request and receive "logical" DMA resources. It is
similar to the IALG interface, which is used to request and grant memory needed by an algorithm.
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IDMA3. All algorithms that use the C64x+ EDMA resources must implement the IDMA3 interface. This
interface allows the algorithm to request and receive “logical” DMA resources. It is similar to the IDMA2
interface in terms of its definition and role, but exposes some physical EDMA3 resources: Parameter
RAM Sets (PaRAMs), Transfer Completion Codes (TCCs), and QDMA Channel ids.
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ACPY2. These functions are implemented as part of the client application and called by the algorithm
(and possibly the client application). A client application must implement the ACPY2 interface (or
integrate a provided ACPY2 interface) in order to use algorithms that use the DMA resource. The
ACPY2 interface describes the comprehensive list of DMA operations an algorithm can perform
62 Use of the DMA Resource SPRU352G – June 2005 – Revised February 2007
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