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AXI (Advanced eXtensible Interface)

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The Advanced eXtensible Interface (AXI) is a point-to-point interconnect protocol designed for high-performance systems. It is part of the ARM AMBA (Advanced Microcontroller Bus Architecture) specification and is widely used in various industries, including aerospace, defense, and telecommunications. In this article, we will explain the key features of the AXI protocol, including its components, transactions, and signaling.

AXI Components

The AXI protocol consists of several components that work together to enable high-speed communication between components. The components of the AXI protocol are as follows:

  1. Master: The master is a component that initiates transactions on the AXI bus. The master can be a processor, DMA controller, or any other component that can initiate transactions.
  2. Slave: The slave is a component that responds to transactions initiated by the master. The slave can be a memory controller, peripheral controller, or any other component that can respond to transactions.
  3. Channel: The channel is a unidirectional communication link between a master and a slave. The AXI protocol uses separate channels for data and control signals to enable high-speed data transfer.
  4. Transaction: A transaction is an exchange of information between a master and a slave. Transactions can be read or write operations, and they can transfer data between the master and the slave.

AXI Transactions

The AXI protocol defines four types of transactions: read, write, read with no data, and write with no data. Each transaction has a specific set of signals that must be asserted to indicate the type of transaction being performed. The following sections describe each type of transaction in more detail.

Read Transaction: A read transaction is initiated by a master to read data from a slave. The master sends an address to the slave, and the slave responds with the data at that address. The read transaction consists of two phases: address phase and data phase.

The address phase involves the master sending the address of the data it wants to read to the slave. The address is sent on the address channel. The master asserts the valid signal to indicate that the address is valid.

In the data phase, the slave responds with the data at the address sent in the address phase. The data is sent on the data channel. The slave asserts the ready signal to indicate that it is ready to send the data.

Write Transaction: A write transaction is initiated by a master to write data to a slave. The master sends an address and data to the slave, and the slave writes the data to the address. The write transaction consists of two phases: address phase and data phase.

The address phase involves the master sending the address of the data it wants to write to the slave. The address is sent on the address channel. The master asserts the valid signal to indicate that the address is valid.

In the data phase, the master sends the data to be written to the slave. The data is sent on the data channel. The master asserts the valid signal to indicate that the data is valid.

Read with No Data Transaction: A read with no data transaction is initiated by a master to read an address range without transferring any data. The read with no data transaction consists of only one phase: address phase.

The master sends the start address and end address of the range to be read to the slave. The addresses are sent on the address channel. The master asserts the valid signal to indicate that the addresses are valid.

Write with No Data Transaction: A write with no data transaction is initiated by a master to write an address range without transferring any data. The write with no data transaction consists of only one phase: address phase.

The master sends the start address and end address of the range to be written to the slave. The addresses are sent on the address channel. The master asserts the valid signal to indicate that the addresses are valid.

AXI Signaling

The AXI protocol uses a set of signals to communicate between the master and slave components. These signals include address, data, control, and status signals. The following sections describe each type of signal in more detail.

  1. Address Signals: The address signals carry the address of the data being read or written. The address signals include the address bus, which carries the actual address, and the address control signals, which include valid and ready signals.
  2. Data Signals: The data signals carry the actual data being read or written. The data signals include the data bus, which carries the actual data, and the data control signals, which include valid and ready signals.
  3. Control Signals: The control signals are used to control the flow of data between the master and slave components. The control signals include read/write, response, burst type, and size signals.
  4. Status Signals: The status signals are used to indicate the status of the transaction. The status signals include response, error, and completion signals.

AXI Protocol Versions

The AXI protocol has evolved over time, and several versions are currently available. The following sections describe each version of the AXI protocol.

  1. AXI: The original AXI protocol was introduced in 2003 and was designed for use in low-power, high-performance systems.
  2. AXI4: The AXI4 protocol was introduced in 2010 and added several new features, including support for burst transactions, atomic operations, and memory-mapped I/O.
  3. AXI4-Lite: The AXI4-Lite protocol was also introduced in 2010 and is a simplified version of the AXI4 protocol. It is designed for use in systems with low gate count and low bandwidth requirements.
  4. AXI4-Stream: The AXI4-Stream protocol was introduced in 2010 and is designed for use in high-bandwidth streaming applications, such as video and audio processing.

Conclusion

In conclusion, the Advanced eXtensible Interface (AXI) protocol is a high-performance interconnect protocol used in various industries. It consists of several components, including master, slave, channel, and transaction, and defines four types of transactions: read, write, read with no data, and write with no data. The AXI protocol uses a set of signals, including address, data, control, and status signals, to communicate between the master and slave components. The AXI protocol has evolved over time, with several versions available, including AXI, AXI4, AXI4-Lite, and AXI4-Stream.