AXI Specification of AMBA

AXI Specification of AMBA

AMBA Specification

1. AHB (Advanced High-Performance Bus)
   A bus designed for high-performance systems, supporting high-bandwidth data transfer between memory and high-speed peripheral devices.
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2. APB (Advanced Peripheral Bus)
   A low-power bus used for communication with slower peripheral devices. It is simpler compared to AHB and is mainly used for tasks such as register access.
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3. AXI (Advanced eXtensible Interface)
   A high-performance, high-bandwidth bus designed for simultaneous data transfer between multiple masters and slaves. Key features include separate read and write data channels, QoS (Quality of Service) support, and flexible memory mapping.

4. AXI4 (Advanced eXtensible Interface 4)
   An extended version of the AXI interface that provides higher performance and efficiency. It includes the following three main subsets
• AXI4: High-bandwidth, high-performance bus
• AXI4-Lite: A simple, low-bandwidth communication bus
• AXI4-Stream: A bus for data streaming
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5. ACE (AXI Coherency Extensions)
   Provides extensions to maintain data coherency in multicore systems.

AXI4 Specification

Key Features of AXI4

1. Independent Read and Write Data Channels
   AXI4 handles read and write requests through independent channels, improving parallel processing performance.

2. Data Burst Transfer
   AXI4 supports continuous data transfers of up to 256 bits, enhancing data transfer efficiency.

3. QoS (Quality of Service) Support
   Manages the priority of data transfers to ensure the transmission of important data.

4. Support for Unaligned Address Transfers
   Provides flexibility by supporting data access to unaligned addresses.

5. Register Slices
   Allows the placement of register slices in the data transfer path to optimize performance.

Components of AXI4

1. Read Address Channel
   Delivers read commands to the slave, including the address and control signals for the read operation.

2. Read Data Channel
   Transfers data from the slave to the master, along with status signals.

3. Write Address Channel
   Delivers write commands to the slave, including the address and control signals for the write operation.

4. Write Data Channel
   Transfers data from the master to the slave, along with control signals.

5. Write Response Channel
   Indicates the completion status of the write operation from the slave to the master.

Subsets of AXI4

1. AXI4
   A high-bandwidth, high-performance bus interface supporting up to 256 data bits.

2. AXI4-Lite
   A simple, low-bandwidth communication interface mainly used for simple tasks such as register access, supporting 32-bit data transfers.

3. AXI4-Stream
   An interface designed for data streaming, suitable for packet-based data transfers. It has minimal overhead and is optimized for continuous data stream transfers.

AXI4-Lite Specification

Key Features of AXI4-Lite

1. Simplified Interface
   The interface is simplified compared to AXI4, making design and implementation easier.

2. 32-bit Data Transfer
   Supports data transfers with a single bit width (32 bits), enabling simple data processing.

3. Single Bit Width Address
   The address bus is also fixed at 32 bits, simplifying address calculations.

4. No Burst Transfers
   AXI4-Lite supports only single transfers and does not have burst transfer capability.

5. Independent Read and Write Channels
   Like AXI4, it uses independent read and write channels to transfer data.

Components of AXI4-Lite

1. Read Address Channel
   The master delivers read commands to the slave, including address and control signals.

2. Read Data Channel
   The slave transfers data to the master, including data and status signals.

3. Write Address Channel
   The master delivers write commands to the slave, including address and control signals.

4. Write Data Channel
   The master transfers data to the slave, including data and control signals.

5. Write Response Channel
   The slave indicates the completion status of the write operation to the master.

Advantages of AXI4-Lite

1. Simplified Design
   The simple interface makes design and implementation easier.

2. Low Resource Consumption
   Optimized design for low-bandwidth communication results in low resource consumption.

3. Compatibility
   Complies with the AMBA standard, ensuring interoperability between various IP blocks.

4. Fewer Pins
   The simplified interface reduces the number of required pins, reducing hardware complexity.

5. Efficient Register Access
   Supports only single transfers, making it suitable for simple tasks such as register access.

Use Cases of AXI4-Lite

1. Register Map Access
   When microcontrollers or processors access the registers of peripheral devices.

2. Low-speed Peripheral Interface
   Interfaces with low-speed peripherals such as SPI and I2C.

3. Simple Data Transfer
   Simple data transfer tasks that do not require high bandwidth.

AXI4 Communication Mechanism

Ready/Valid Handshake Mechanism

1. Valid
   The side that intends to send data (master or slave) activates the VALID signal along with the data. This indicates that the data is valid and ready to be transmitted.

2. Ready
   The side that intends to receive data (slave or master) activates the READY signal. This indicates that it is ready to receive the data.
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Handshake for Each AXI Channel

1. Read Address Channel
• ARVALID: Indicates that the master is ready to send the read address and control information.
• ARREADY: Indicates that the slave is ready to receive the read address and control information.
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2. Read Data Channel
• RVALID: Indicates that the slave is ready to send the read data.
• RREADY: Indicates that the master is ready to receive the read data.
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3. Write Address Channel
• AWVALID: Indicates that the master is ready to send the write address and control information.
• AWREADY: Indicates that the slave is ready to receive the write address and control information.
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4. Write Data Channel
• WVALID: Indicates that the master is ready to send the write data.
• WREADY: Indicates that the slave is ready to receive the write data.
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5. Write Response Channel
• BVALID: Indicates that the slave is ready to send the write response.
• BREADY: Indicates that the master is ready to receive the write response.

Write Data Transfer Example

1. Write Address Transfer
• AWVALID: The master activates the AWVALID signal to indicate it is ready to send the write address and control information to the slave.
• AWREADY: The slave activates the AWREADY signal to indicate it is ready to receive the write address and control information.
• Address Transfer: The write address and control information are transferred in the clock cycle when both AWVALID and AWREADY signals are activated.
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2. Write Data Transfer
• WVALID: The master activates the WVALID signal to indicate it is ready to send the write data to the slave.
• WREADY: The slave activates the WREADY signal to indicate it is ready to receive the write data.
• Data Transfer: The write data is transferred in the clock cycle when both WVALID and WREADY signals are activated. This process can repeat as needed, with each transfer being part of a data burst.
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3. Write Response Transfer
• BVALID: The slave activates the BVALID signal to indicate it is ready to send the write response to the master.
• BREADY: The master activates the BREADY signal to indicate it is ready to receive the write response.
• Response Transfer: The write response is transferred in the clock cycle when both BVALID and BREADY signals are activated. The response includes success or failure status.

Read Data Transfer Example

1. Read Address Transfer
• ARVALID: The master activates the ARVALID signal to indicate it is ready to send the read address and control information to the slave.
• ARREADY: The slave activates the ARREADY signal to indicate it is ready to receive the read address and control information.
• Address Transfer: The read address and control information are transferred in the clock cycle when both ARVALID and ARREADY signals are activated.
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2. Read Data Transfer
• RVALID: The slave activates the RVALID signal to indicate it is ready to send the read data to the master.
• RREADY: The master activates the RREADY signal to indicate it is ready to receive the read data.
• Data Transfer: The read data is transferred in the clock cycle when both RVALID and RREADY signals are activated. This process can repeat as needed, with each transfer being part of a data burst.