What is the difference between processor A76 architecture and A77 architecture?

The difference between processor A76 architecture and A77 architecture

1. A77 has twice the branch predictor than A76;

2. A77 directly allows instructions to enter the CPU central renaming stage in the case of a cache hit, which reduces the length of the computing pipeline and improves efficiency by 30%.

Cortex-A77

From the perspective of product development generations, Cortex-A77 is the direct successor of Cortex-A76 , which means that the new architecture is basically the same as the previous generation product. ARM said that Cortex-A77 only needs to simply upgrade the SoC IP to deploy, and does not need to tear down and start from scratch.

Corresponding to the actual product, Cortex-A77, like Cortex-A76, still uses the ARMv8.2 CPU core and supports AArch32 and AArch64. In terms of multi-core design, Cortex-A77 still supports DSU (DynamIQ Shared Uint) to pair with the smaller Cortex-A55 unit. In terms of basic architectural configuration, Cortex-A77 still supports 64KB L1 instruction and data cache and 256KB or 512KB L2 cache.

Interestingly, ARM chose a smaller capacity solution for the L2 cache design of Cortex-A77, because its infrastructure-oriented Neoverse N1 processor architecture uses a 1MB L2 cache. This The architecture of the processor itself comes from Cortex-A76, which may mean that ARM has more unique ideas in processor configuration.

According to experience, as an evolution of the Cortex-A76 architecture, from a micro-architectural perspective, the performance improvement of Cortex-A77 should not be very large, and the same should be true from an absolute performance perspective. After all, the craftsmanship has not improved significantly at this time point. Most Cortex-A77 products will still use the 7nm process. ARM claims that the peak frequency of Cortex-A77 is the same as the previous generation Cortex-A76, which is 3GHz. If this is the case, the Cortex-A77 may not have much to offer.

But according to the roadmap released by ARM, Cortex-A77 can bring a 20% performance improvement compared to the previous generation products. Considering that it has not changed much in terms of process and frequency, this means that the architecture of Cortex-A77 will have obvious changes, and the IPC has been significantly improved. In fact, ARM has redesigned the Cortex-A77 architecture and introduced a large number of intelligent functions, thus bringing about a performance increase of up to 20% while the process and frequency remain unchanged.

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