Editing samsung/microarchitectures/m4

{{samsung title|Exynos M4|arch}}
{{microarchitecture
|atype=CPU
|name=Cheetah
|designer=Samsung
|manufacturer=Samsung
|introduction=2019
|process=8 nm
|cores=4
|type=Superscalar
|type 2=Superpipeline
|oooe=Yes
|speculative=Yes
|renaming=Yes
|stages=16
|decode=6-way
|isa=ARMv8.2
|l1i=64 KiB
|l1i per=core
|l1i desc=4-way set associative
|l1d=64 KiB
|l1d per=core
|l1d desc=8-way set associative
|l2=512 KiB
|l2 per=core
|l2 desc=8-way set associative
|l3=2 MiB
|l3 per=cluster
|l3 desc=16-way set associative
|predecessor=M3
|predecessor link=samsung/microarchitectures/m3
|successor=M5
|successor link=samsung/microarchitectures/m5
}}
'''Exynos Cheetah''' ('''M4''') is the successor to the {{\\|M3}}, an [[8 nm]] [[ARM]] microarchitecture designed by [[Samsung]] for their consumer electronics.

== Process Technology ==
The M4 is fabricated on Samsung's [[8 nm process]] (8LPP).

== Compiler support ==
{| class="wikitable"
|-
! Compiler !! Arch-Specific || Arch-Favorable
|-
| [[GCC]] || <code>-mcpu=exynos-m4</code> || <code>-mtune=exynos-m4</code>
|-
| [[LLVM]] || <code>-mcpu=exynos-m4</code> || <code>-mtune=exynos-m4</code>
|}


== Architecture ==
The M4 is an incremental microarchitecture that brought a die shrink and minor enhancements.

=== Key changes from {{\\|Mongoose 3|M3}} ===
* [[8 nm process]] (from [[10 nm]])
* [[ARMv8.2]] (from [[ARMv8]])
** Support for full FP16 scalar extension
** Support for integer dot product extension
* Front end
** Larger [[instruction queue]] (48 entries, up from 40)
* Back end
** LSU executiion units reorganized
** Floating-point execution units reorganized
{{expand list}}

=== Block Diagram ===
==== Individual Core ====

[[File:mongoose 4 block diagram.svg|900px]]

=== Memory Hierarchy ===
* Cache
** L1I Caches
*** 64 KiB, 4-way set associative
**** 128 B line size
**** per core
*** Parity-protected
** L1D Cache
*** 64 KiB, 8-way set associative
**** 64 B line size
**** per core
*** 4 cycles for fastest load-to-use
*** 32 B/cycle load bandwidth
*** 16 B/cycle store bandwidth
** L2 Cache
*** 512 KiB, 8-way set associative
*** Inclusive of L1
*** 12 cycles latency
*** 32 B/cycle bandwidth
** L3 Cache
*** 2 MiB, 16-way set associative
**** 1 MiB slice/core
*** Exlusive of L2
*** ~37-cycle typical (NUCA)
** BIU
*** 80 outstanding transactions

The M3 TLB consists of dedicated L1 TLB for instruction cache (ITLB) and another one for data cache (DTLB). Additionally, there is a unified L2 TLB (STLB).

* TLBs
** ITLB
*** 512-entry
** DTLB
*** 32-entry
*** 512-entry Mid-level DTLB
** STLB
*** 4,096-entry
*** Per core

* BPU
** 4K-entry main BTB
** 128-entry µBTB
** 64-entry return stack
** 16K-entry L2 BTB

== Core ==
The core of the M4 is largely the same as {{\\|M3}}. A number of buffers have been enlarged and some of the execution units have been reorganized.

=== Execution engine ===
==== Floating-point cluster ====
The execution units on the M4 have been reorganized. In total, three new units were also added  - a second FP square root unit, a second vector multiplication unit, and a new horizontal vector arithmetic unit.

:[[File:m4 fp eu pipes changes.svg|thumb|left|600px|Floating-point pipe changes.]]

{{clear}}

==== Memory subsystem ====
[[File:m4 data cache.svg|thumb|left]]
Samsung also made an enhancement to the M4 memory subsystem. In the M3, there were three AGUs - two dedicated Load [[AGUs]] and a single dedicated Store [[AGU]]. In the M4, Samsung changed one of the dedicated Load [[AGU]]s into a generic AGU capable of handling both loads and stores. In other words, the M4 can now schedule both load and store µOPs on two ports.

{{clear}}

== All M4 Processors ==
<!-- NOTE: 
           This table is generated automatically from the data in the actual articles.
           If a microprocessor is missing from the list, an appropriate article for it needs to be
           created and tagged accordingly.

           Missing a chip? please dump its name here: https://en.wikichip.org/wiki/WikiChip:wanted_chips
-->
{{comp table start}}
<table class="comptable sortable tc5 tc6 tc7">
{{comp table header|main|7:List of M4-based Processors}}
{{comp table header|main|5:Main processor|2:Integrated Graphics}}
{{comp table header|cols|Family|Launched|Arch|Cores|%Frequency|GPU|%Frequency}}
{{#ask: [[Category:microprocessor models by samsung]] [[microarchitecture::Mongoose 4]]
 |?full page name
 |?model number
 |?family
 |?first launched
 |?microarchitecture
 |?core count
 |?base frequency#GHz
 |?integrated gpu
 |?integrated gpu base frequency
 |format=template
 |template=proc table 3
 |userparam=9
 |mainlabel=-
 |valuesep=,
}}
{{comp table count|ask=[[Category:microprocessor models by samsung]] [[microarchitecture::Mongoose 4]]}}
</table>
{{comp table end}}

== Bibliography ==
* LLVM: lib/Target/AArch64/AArch64SchedExynosM4.td
codename	Cheetah +
core count	4 +
designer	Samsung +
first launched	2019 +
full page name	samsung/microarchitectures/m4 +
instance of	microarchitecture +
instruction set architecture	ARMv8.2 +
manufacturer	Samsung +
microarchitecture type	CPU +
name	Cheetah +
pipeline stages	16 +
process	8 nm (0.008 μm, 8.0e-6 mm) +