Architecture Exploration

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Adding DMA Controller

Purpose of this tutorial is to understand the impact of a Direct Memory Access on the model built in Scenario 4.

VisualSim Model

Refer Fig 1 for the intended VisualSim Model.

Figure 1: VisualSim Model

VisualSim Model for the tutorial can be found in following location

$VS\doc\Training_Material\Tutorial\WebHelp\Tutorial\Architecture_Exploration\Processor_Modeling_Tutorial\Processor_Modeling_Part1_DMA.xml

Building the VisualSim Model

Blocks Used

In addition to the blocks used in Scenario 4, this model uses the blocks listed in the following table.

S.No.	Library Block	Description
1	Device Interface	This block adds the device name to the Routing Table and maps the incoming data structures fields to the equivalent in the Processor_DS. Click here for detailed description and examples.
2	DMA	This block represents a memory controller that sits between the Processor or bus or I_O Block and the Memory bank. The IO Controller acts as an intermediate block and just transfers the transactions from bus or DMA Controller to appropriate memory bank or devices connected to the IO Controller. Click here for further details.
3	DMA Database	This block is a lookup table or database containing rows and columns. Each row is a data structure. Each column of the row is a field of the data structure. Click here for further details.

Initial Setup

Define the following additional parameter from Model Setup.

DMA_Bytes: 64

Sets the value for the size of the tasks (Store and Load).

Architectural Elements

Add the following architectural elements to the ones existing in scenario 4.

Drag and drop a Traffic block from Traffic to represent a device that generate transaction.
In the Traffic block,

Enter the Data_Structure_Name as "Processor_DS".
Enter Value_1 as 1.0e-3.
Select Time_Distribution as Fixed (Value_1).

Figure 1: Traffic Parameters

Add an ExpressionList block from Behavior to categorize the instruction as Store or Load.

Define the following fields in the Expression_List parameter.

RandNum = irand(1,100)

Generate random numbers to assist in the selection of tasks.

input.A_Source = "Display_Intf"

Adds a field to the datastructure to store the name of the device that sends the transactions.

input.A_Instruction = (RandNum >= 50)?{"Store"}:{"Load"}

Use random numbers to select a task.

input.A_Task_Flag = true

This flag is set to true when the memory sends an acknowledgment for a Store task. Then, the behavior flow is triggered.

input.A_Task_Name = "Display_Task"

Adds a field to the datastructure to store the name of the task.

input.A_Bytes = DMA_Bytes

Adds a field to store the value for the size of a task. This value is set as part of the initial parameters.

The rest of the parameters retain the default settings.

Figure 2: ExpressionList Parameters

Add a DeviceInterface block from HardwareSetup.
In the DeviceInterface block enter,

IO_Name as "Display_Intf"
IO_Bytes as "A_Bytes"

The rest of the parameters retain the default settings.

Figure 3: Device Interface Parameters

Drag and drop a DMADatabase block to store the details of the tasks.
In the DMADatabase block,enter Linking_Name as "DMA_DB".
Enter the following details in the Data_Structure_Text parameter.

A_Task_Name    A_Instruction    A_IDX    A_Task_Source    Burst_Word_Size    A_Task_Address A_Command    A_Bytes    A_Priority    A_Destination    ;
Display_Task     Load              0       DRAM                  32            1          Read               DMA_Bytes         0                 DMA ;
Display_Task    Store              0       DRAM                  32            1          Write       DMA_Bytes         1                 DMA ;