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Keeping the instruction stream feed is the task of the branch prediction unit. Like the {{\\|Enyo}}, the branch prediction unit on Deimos is decoupled from the instruction fetch, allowing it to run ahead and in parallel with the instruction fetch to hide branch prediction latency. Since the instruction fetch has been increased, Arm also doubled the branch predictor instruction window size to 64 bytes/cycle, in order to allow it to runahead of the instruction stream. The main [[branch target buffer]] on the A77 has been increased by 33% compared to A76. It is now 8K-entries deep which Arm says directly improves the real-world performance of many workloads. The BPU comprises three stages in order to reduce latency with a 64-entry micro-BTB and a smaller 64-entry nano BTB which has been quadrupled in size from 16 entries in the A76. | Keeping the instruction stream feed is the task of the branch prediction unit. Like the {{\\|Enyo}}, the branch prediction unit on Deimos is decoupled from the instruction fetch, allowing it to run ahead and in parallel with the instruction fetch to hide branch prediction latency. Since the instruction fetch has been increased, Arm also doubled the branch predictor instruction window size to 64 bytes/cycle, in order to allow it to runahead of the instruction stream. The main [[branch target buffer]] on the A77 has been increased by 33% compared to A76. It is now 8K-entries deep which Arm says directly improves the real-world performance of many workloads. The BPU comprises three stages in order to reduce latency with a 64-entry micro-BTB and a smaller 64-entry nano BTB which has been quadrupled in size from 16 entries in the A76. | ||
− | Deimos has a fixed 64 KiB L1I cache. It is [[virtually indexed, physically tagged]] (VIPT), which behaves as a [[physically indexed, physically tagged]] (PIPT) 4-way set-associative cache. The L1I$ supports optional parity protection and implements a [[pseudo-LRU]] [[cache replacement]] policy. The instruction cache has a 256-bit read interface from the L2 cache. Each cycle up to | + | Deimos has a fixed 64 KiB L1I cache. It is [[virtually indexed, physically tagged]] (VIPT), which behaves as a [[physically indexed, physically tagged]] (PIPT) 4-way set-associative cache. The L1I$ supports optional parity protection and implements a [[pseudo-LRU]] [[cache replacement]] policy. The instruction cache has a 256-bit read interface from the L2 cache. Each cycle up to 32 bytes may be transferred to the L1I cache from the shared L2 cache. |
− | From the instruction fetch, up to | + | From the instruction fetch, up to six 32-bit instructions are sent to the decode queue (DQ) each cycle. This is two additional instructions per cycle more than the {{\\|Enyo}} and is the widest pipeline Arm designed to that point. For narrower 16-bit instructions (i.e., {{arm|Thumb}}), this means up to twelve instructions get queued. The A76 features a 6-way decode. Each cycle, up to six instructions may be decoded into a relatively semi-complex [[macro-operations]] (MOPs). There are on average 6% more MOPs than instructions. In total two cycles are involved in this operation - one for alignment and one for decode. |
==== Back-end ==== | ==== Back-end ==== |
Facts about "Cortex-A77 - Microarchitectures - ARM"
codename | Cortex-A77 + |
core count | 1 +, 2 +, 4 +, 6 + and 8 + |
designer | ARM Holdings + |
first launched | May 27, 2019 + |
full page name | arm holdings/microarchitectures/cortex-a77 + |
instance of | microarchitecture + |
instruction set architecture | ARMv8.2 + |
manufacturer | TSMC +, samsung + and SMIC + |
microarchitecture type | CPU + |
name | Cortex-A77 + |
pipeline stages | 13 + |
process | 10 nm (0.01 μm, 1.0e-5 mm) +, 7 nm (0.007 μm, 7.0e-6 mm) + and 5 nm (0.005 μm, 5.0e-6 mm) + |