RFAMBA AHB vs AXI: Key Differences Explained
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This article compares AMBA AHB and AXI, highlighting the key differences between these two important AMBA (Advanced Microcontroller Bus Architecture) interface bus types.
Introduction to AMBA
AMBA stands for Advanced Microcontroller Bus Architecture. It defines AMBA protocols used for connections on boards with various functional blocks and peripherals. This is especially useful when you have multiple microcontrollers, microprocessors, memory, DSPs, DMAs, USBs, PCI, I2C, and other peripherals on a single board.
Figure 1: AMBA standard evolution timeline
AMBA standards cover various bus types, including:
- AHB (Advanced High-performance Bus)
- ASB (Advanced System Bus)
- APB (Advanced Peripheral Bus)
- ATB (Advanced Trace Bus)
- AXI (AMBA Extensible Interface)
AMBA AHB (Advanced High-Performance Bus)
AMBA AHB is designed for high-performance, high clock frequency system modules. It allows efficient connection of processors, on-chip memories, and off-chip external memory interfaces.
Key features of AMBA AHB:
- High performance
- Pipelined operation
- Multiple bus masters
- Burst transfers
- Split transactions
- Single clock edge operation
- Single cycle bus master handover
- Non-tristate implementation
- Wide data bus configurations (64/128 bits)
Figure 2: AMBA AHB Architecture
Figure 2 shows an AMBA-based SoC design using AHB or ASB protocols for high-bandwidth interconnects and APB protocol for low-bandwidth peripheral interconnects. An AHB to APB bridge or ASB to APB bridge connects the high-bandwidth and low-bandwidth peripherals.
AMBA AXI (AMBA Extensible Interface)
AMBA AXI is designed for high-performance, high-frequency, and high-speed submicron interconnect. It’s well-suited for high-bandwidth and low-latency designs. It’s also backward compatible with previous interfaces like AHB and APB. AXI enables high-frequency operation without the need for complex bridges.
Figure 3: AMBA AXI architecture
There are different versions of AXI interfaces, including AXI3, AXI4, and AXI-Lite, each defined in various standard specifications.
As shown in Figure 3, an AXI system consists of multiple master and slave devices connected using interconnects.
AMBA AHB vs. AMBA AXI: Key Differences
The following table highlights the comparison between AMBA AHB and AMBA AXI:
| Features | AMBA AHB Bus | AMBA AXI Bus |
|---|---|---|
| Architecture | Single channel, Shared bus | Multi-channel, read/write optimized bus |
| Bus width and Speed | 128-bit bus running at 400 MHz | 64-bit bus running at 200 MHz |
| Burst mechanism | Address and data are locked together (single pipeline stage), HREADY controls intervals for address and data | One address for the entire burst, simultaneous read and write transactions |
| Address Transmission | Requires transmitting the address of every data item transmitted on the bus | better bus utilization as burst mode requires transmitting address of only the first data item on the bus. |
| Throughput | Good | Excellent |
| Latency | Excellent | Good |
| Power consumption | Low | High |
| Burst mode | No fixed burst mode | Fixed burst mode for memory-mapped I/O peripherals |
| Access | No exclusive access support | Exclusive data access (semaphore operation) support |
| Security | Simple protection and cache hint support | Advanced security and cache hint support |
| Timing Isolation | No inherent support for timing isolation | Register slice support for timing isolation |
| Power interface | No low power interface | Native low power clock control interface |
| Topology | Default hierarchical bus topology support | default bus matrix topology support |
