About this Application Note

The Multi-Instance AWE Core Integration Guide is meant to guide users who wish to implement multiple instances of AWE Core and take advantage of the IPC audio routing and tuning communication features of AWE Core.

AWE Core Instance Overview

An instance of AWE Core can be thought of as the smallest individual addressable unit of AWE Core on an embedded target.

A single instance of AWE Core:

• Has its own:

  • Unique Instance Id

  • Sampling rate and block size

  • Number of I/O channels

  • Set of AWE Core heaps (Fast, Fastb, Slow)

  • Module Table (ModuleList.h)

  • Number of processing threads

• Is initialized once using awe_init()

• Processes tuning packets addressed to its Instance Id

• Performs audio processing on modules assigned to its Instance Id

When using Audio Weaver with an embedded target, it is mandatory to configure and initialize at least one AWE Core instance. In some applications and hardware configurations, creating two or more AWE Core instances on a target is desired.

Configuring multiple instances of AWE Core allows you to:

• Distribute audio processing across multiple processing cores in a single design

• Increase parallelism by assigning each AWE Core instance to a unique OS thread

• Architect groups of features into their own instance to better monitor and analyze feature behavior

  • AWE Designer profiles CPU and memory usage per individual instance

Standard SoC Architecture Example

Consider a standard multicore SoC architecture:

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Figure 1. Generic Audio SoC Architecture

In this SoC architecture, there are two separate processing cores.

Core 0 has:

• Access to the tuning interface

• Access to all Audio I/O peripherals

• Access to shared memory region

• Its own internal memory region

Core 1 has:

• Access to shared memory region

• Its own internal memory region

In this typical multicore SoC architecture, an instance of AWE Core can be placed on each core. The shared memory of the SoC is utilized by AWE Core to communicate between the two instances, as well as buffer audio data between instances. AWE Core handles all data exchange between instances; no user protocol or software needs to be written to facilitate.

Setting Up Multi-Instance AWE Core

Initializing Shared Heap

To facilitate multi-instance with AWE Core, each AWE Core instance requires an initialization of the shared heap.

The shared heap is a contiguous section of memory which occupies the same physical address space for all AWE Core instances.

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Figure 2. Shared Address Space Architecture

pSharedHeap points to this contiguous segment of memory. Every AWE Core instance in use is required to point to the same shared memory region address space. For this reason, shared heap must be placed in a shared memory region.

The size of this region is provided to AWE Core using sharedHeapSize.

Handling Multi-Instance Tuning Packets

Multi-instance AWE Core requires that the tuning packet buffer registered to each AWE Core instance occupy the same contiguous address space (see Figure 2).

Additionally, the pReplyBuffer reply buffer pointer registered to each AWE Core instance is required to point to the same packet buffer for multi-instance, as multi-instance AWE Core processes tuning packets in place.

Each instance processes packets with the AWE Core API awe_packetProcessMulti().

Tuning Master Instance Usage

On the tuning master instance, this API is called whenever a complete packet has been received and is ready to be processed.

When this API returns E_MULTI_PACKET_WAITING, the packet has been forwarded to another instance to process. When this happens, this API should be repeatedly called by the tuning master instance until the return value changes. Only when a return value other than E_MULTI_PACKET_WAITING is received should the reply buffer be read and sent back to AWE Server.

See Core 0 Packet Processing for a usage example.

Non-Tuning Instance Usage

For non-tuning interface instances, this API is polled continuously. This is done so that the calling instance can check if it has been flagged by the tuning master instance and handle any packet processing if required.

For both tuning and non-tuning instances, the awe_packetProcessMulti() API must be called in a low-priority task, so as to not hold off audio processing.

See Core 1 Packet Processing for a usage example.

Assigning Unique Instance Ids

AWE Core’s instanceId parameter is used by AWE Designer to identify and address tuning packets to specific instances on an embedded target. For this reason, it is required that each AWE Core instance be registered with a unique instance Id.

The instanceId naming convention follows a linear increment starting at 0 (e.g. 0, 1, 2, etc..).

There are a few special behaviors assigned to the AWE instance with an instanceId of 0:

• instanceId 0 must be the instance interacting with the embedded target’s tuning interface

• instanceId 0 is the only instance that can use the System input/output pins of an Audio Weaver design. Consequently, it is the only instance which can use the awe_audioImportSamples() and awe_audioExportSamples()

The total number of AWE Core instances used in the application are provided to each instance with numProcessingInstances.

Processing Audio in Multi-Instance AWE Core

All AWE Core instances handle processing of audio in the same manner. Each instance has its own pump mask, retrieved with awe_audioGetPumpMask(), and uses the returned value to trigger the corresponding layout(s) to pump.

For multi-instance audio processing to function, each instance requires the same fundamental block size, as well as a unified global audio interrupt to synchronize all AWE Core instances.

It is required to trigger all instances on the target synchronously with the rate of audio buffer I/O. This is a user-specific piece of logic that could be a global RTOS event, global system software interrupt, or other similar logic. Most commonly, this means that a user must flag an interrupt in an audio DMA routine which all cores containing AWE Core instances react and trigger processing to.

Code Example for Standard SoC Architecture

Consider the generic SoC architecture from the Standard SoC Architecture Example.

Core 0 Initialization

Core 0 has a single AWE Core instance and allocates a shared heap memory segment before passing it to its AWE Core instance.

The memory section “.shared_heap” is defined to reside in the “shared memory” region of the SoC. Similarly, “.shared_packet” is defined to in the same shared memory region. This is to enforce the AWE Core requirement that all AWE Core instances must have access to the shared heap and packet buffer.

Core 1 Initialization

Similar logic is placed on Core 1, taking care that g_shared_heap and g_PacketBuffer are allocated in the exact same address space as on Core 0, and that this AWE Core instance receives a unique instanceId.

Core 0 Packet Processing

Finally, the multi-instance packet process API must be called in each core. Core 0 is the core containing the tuning interface, and triggers the packet process API only when a complete packet has been received.

Core 1 Packet Processing

Core 1 is not attached to the tuning interface, and only needs to repeatedly poll the packet process API.

Core 0 Audio Processing Synchronization

Instance 0 is the only instance which interfaces with AWE Designer’s I/O pins, and is also the instance which needs to synchronize the audio processing of every other instance.

Below is a generic code snippet of what an audio processing routine on instance 0 would look like.

Core 1 Audio Processing Synchronization

Core 1 does not have any physical audio I/O connected to it. Core 1 also needs to react to Core 0’s global interrupt flag to process its own audio. No import or export API is called, because only instance 0 can interface with AWE Designer’s I/O pins.

Creating multi-instance designs in Audio Weaver

Audio Weaver provides a single design canvas which can place modules on any instance. Audio data can be routed between instances in one design file, which allows users to move processing loads seamlessly to available cores on an embedded target. The below example canvas has processing distributed over two AWE Core instances residing on two different processing cores.

When connected to a multi-instance target, AWE Designer will show a module’s current instance ID below the module:

The instance ID of a module is propagatable between modules, which means that if the output of a module on instance ID 0 is routed to another module, that second module will inherit the instance ID and process on instance ID 0 as well.

There are two ways of changing the instance ID of a module.

• Using the IPCBuffer module

• (Source modules only) Modify the clockDivider field of a module

IPCBuffer Module

The IPCBuffer module is a simple module which takes an input data wire, and using a tunable parameter targetInstance, directs this data to a new instance. Modules connected to the output of the IPCBuffer module will inherit this new instance ID.

Changing the instance ID of a Source module

For source modules (modules which do not have an input wire), one can change the instance ID by modifying the clockDivider field of the module.

Take as an example a sine generator module:

When dragged into the canvas, the module always defaults to ‘Instance 0’.

To reach the clockDivider field, right-click on the module and select View Properties.

In the bottom pane that appears, select the Build tab, and locate the clockDivider field.

The encoding for the clockDivider field is Thread ID + Instance ID.

As an example, let’s keep the thread ID in its default thread of ‘1A’. However, it is desired in this example to change the instance ID to 1. Thus, the clockDivider field should be set to ‘1A1’.

Finally, click the Propagate Changes button at the top of Designer to register the change with the module. The resulting module text will update to report the change in Instance ID.

Loading Multi-Instance Designs in AWE Core

Multi-instance designs created in Designer are exported as a single binary file (in .awb or C array format) which encompasses all AWE instances.

Multi-instance designs are required to be loaded from the tuning master instance. If the AWE Core flash file system is used for storing and loading a multi-instance design, the flash file system is required to be attached to the tuning master instance. Similarly, when loading a multi-instance design by a static C array, the C array must be read by the tuning master instance.

At the time a multi-instance design is loaded, all AWE instances must be initialized. Failure to ensure this sequencing can result in the multi-instance design load to infinitely pend on a response from an uninitialized instance.

Loading multi-instance designs on a single-core target

A single-core architecture can support multi-instance AWE Core, where both a tuning master instance and non-tuning instance(s) exist on the same core. In this architecture, one additional integration step is required when loading a multi-instance design.

AWE Core needs to access all instances on the core to load a multi-instance design. The API awe_setInstancesInfo() is used to register these instances with AWE Core. This API needs to be called before any multi-instance design is loaded.

See the following usage example:

Summary

Utilizing multi-instance AWE Core requires these steps:

1. Allocate a shared heap memory space in a memory region accessible to all AWE Core instances.

2. Allocate the tuning packet buffer in a shared memory region accessible to all AWE Core instances. Initialize the reply buffer pointer to the same memory region as the packet buffer.

3. For each AWE Core instance, provide the shared heap and shared packet buffer, ensuring they occupy the same address space in memory for each instance.

4. Provide a unique instanceId to each AWE Core instance, with instanceId 0 reserved for the AWE Core instance connected to the tuning interface.

5. Set the numProcessingInstances member of each AWE Core instance to the total number of AWE Core instances on the target system.

6. Using a global software interrupt accessible to all AWE Core instances, trigger each instance to check their pump mask and pump. This trigger is required to be synchronous to the audio peripheral data passed in/out of AWE Core instance 0.

7. Process packet buffer data using the multi-instance packet process API. For the tuning master instance, the API is called once a complete packet is received. For non-tuning instances, the API is polled in a low-priority task.