Editing intel/microarchitectures/silvermont

{{intel title|Silvermont|arch}}
{{microarchitecture
| atype            = CPU
| name          = Silvermont
| designer      = Intel
| manufacturer  = Intel
| introduction  = 2013
| phase-out     = 2015
| process       = 22 nm
| cores         = 1
| cores 2       = 2
| cores 3       = 4
| cores 4       = 8

| pipeline      = Yes
| type          = Superscalar
| OoOE          = Yes
| speculative   = Yes
| renaming      = Yes
|isa=x86-64
| stages min    = 12
| stages max    = 14
| issues        = 2

| inst          = Yes
| feature       = 
| extension     = MOVBE
| extension 2   = MMX
| extension 3   = SSE
| extension 4   = SSE2
| extension 5   = SSE3
| extension 6   = SSSE3
| extension 7   = SSE4.1
| extension 8   = SSE4.2
| extension 9   = POPCNT
| extension 10  = AES
| extension 11  = PCLMUL
| extension 12  = RDRND

| cache         = Yes
| l1i           = 32 KiB
| l1i per       = Core
| l1i desc      = 8-way set associative
| l1d           = 24 KiB
| l1d per       = Core
| l1d desc      = 6-way set associative
| l2            = 1 MiB
| l2 per        = 2 Cores
| l2 desc       = 16-way set associative

| core names       = Yes
| core name        = Tangier
| core name 2      = Valleyview
| core name 3      = Avoton
| core name 4      = Rangeley

| succession       = Yes
| predecessor      = Saltwell
| predecessor link = intel/microarchitectures/saltwell
| successor        = Airmont
| successor link   = intel/microarchitectures/airmont
}}
'''Silvermont''' ('''SLM''') is [[Intel]]'s [[22 nm]] [[microarchitecture]] for the {{intel|Atom|Atom family}} of [[system on chip]]s. Introduced in 2013, Silvermont was the successor to {{intel|Saltwell}}, targeting smartphones, tablets, embedded devices, and consumer electronics.

== Codenames ==
{| class="wikitable"
|-
! Platform !! Core !! Target
|-
| {{intel|Merrifield}} || {{intel|Tangier}} || Smartphones
|-
| {{intel|Moorefield}} || {{intel|Anniedale}} || High-end Smartphones
|-
| {{intel|Slayton}}    ||  {{intel|SoFIA}} || Smartphones (3G only)
|-
| {{intel|Bay Trail}} || {{intel|Bay Trail}} || Tablets
|-
| {{intel|Edisonville}} || {{intel|Avoton}} || Microservers
|-
| {{intel|Edisonville}} || {{intel|Rangeley}} || Embedded Networking
|}

== Process Technology ==
{{main|intel/microarchitectures/ivy bridge#Process_Technology|l1=Ivy Bridge § Process Technology}}
Silvermont-based chips are manufactured on Intel's [[22 nm process]].

== Architecture==
Silvermont introduced a number of significant changes from the {{intel|Saltwell|previous}}  {{intel|Atom}} microarchitecture in addition to the increase performance and lower power consumption.

=== Key changes from {{intel|Saltwell}} ===
* Pipeline is now OoOE
* 14 stage (2 shorter)
* 10 stage panelty for miss (3 shorter)
* Support up to {{intel|Westmere}}
* Multi-core modular system (up to 8 cores)

==== New instructions ====
Silvermont introduced a number of {{x86|extensions|new instructions}}:

* {{x86|SSE4.1|<code>SSE4.1</code>}} - Streaming SIMD Extensions, Version 4.1
* {{x86|SSE4.2|<code>SSE4.2</code>}} - Streaming SIMD Extensions, Version 4.2
* {{x86|MOVBE|<code>MOVBE</code>}} - Move Big-Endian instruction
* {{x86|CRC32|<code>CRC32</code>}} - [[Hardware-accelerated]] [[CRC32]]
* {{x86|POPCNT|<code>POPCNT</code>}} - Hardware-accelerated [[population count]]
* {{x86|CLMUL|<code>CLMUL</code>}} - Hardware-accelerated Carry-less Multiplication
* {{x86|AES|<code>AES</code>}} - Hardware-accelerated AES operations
* {{x86|RDRAND|<code>RDRAND</code>}} - Secure Key Technology extension
* {{x86|PREFETCHW|<code>PREFETCHW</code>}} - Prefetch data into caches, hinting a write is expected in the future

=== Block Diagram ===
[[File:silvermont block.png]]

=== Core Modules ===
[[File:silvermont modules.svg|right|450px]]
Silvermont employees a modular core design. Each module consists of 2 cores and 2 threads with exclusive hardware - resources are not shared. Within each module is a 1 MB L2 cache shared between the two cores. The L1 is still identical to {{intel|Saltwell|Saltwell's}}: 32K L1I$ and 24K L1D$. Each module as a dedicated point-to-point interface (IDI) to the system agent. Each module has a per-core frequency and power management support. This is a departure from previous microarchitectures as well as similar desktop (e.g. Core) where all cores are tied to the same frequency.

==== System Agent ====
The system agent (''Silvermont System Agent''') acts very much like a [[North Bridge]] however it does a much better job than previous {{intel|Atom}} microarchitectures performance-wise because it's capable of reordering all requests from all consumers (e.g. Core, GPU). 

==== IDI ====
While the previous {{intel|Atom}} architecture did away with the memory controller by integrating and other support chips on-die, it still used a Front Side Bus implementation to talk to North Bridge. In Silvermont, this was replaced with a lightweight in-die interconnect (IDI) - same one used in the {{\\|Core}} processors. The use of IDI should have noticeable performance impact per thread.

=== Memory Hierarchy ===
* Cache
** Hardware prefetchers
** L1 Cache:
*** 32 [[KiB]] 8-way [[set associative]] instruction, 64 B line size
*** 24 KiB 6-way set associative data, 64 B line size
*** Per core
** L2 Cache:
*** 1 MiB 16-way set associative, 64 B line size
*** Per 2 cores
*** 32B/cycle, 14 cycle latency
** L3 Cache:
*** No level 3 cache
** RAM
*** Maximum of 1 GiB, 2 GiB, and 4 GiB
*** dual 32-bit channels, 1 or 2 ranks per channel

=== Multithreading ===
Silvermont dropped support for Intel Hyper-Threading Technology.

=== Pipeline ===
While Silvermont share some similarities with {{\\|Saltwell}}, it introduces a number of significant changes that sets it apart from part {{intel|Atom}} microarchitectures. Like {{\\|Saltwell}}, the pipeline is still uses a dual-issue design; however it has a pipeline that is 2 stages shorter with a branch misprediction penalty of 3 cycles lower. Silvermont is the first microarchitecture to introduce [[out-of-order execution]] (OoOE) 

[[File:silvermont pipeline.svg]]

Silvermont pipeline decodes and issues 2 instructions and dispatches 5 operations/cycle.

==== Instruction Fetch ====
Instruction Fetch, just like in previous microarchs make up the first three stages of the pipeline. However, with the introduction of out-of-order execution, silvermont's more aggressive fetching and branch prediction mean stalled instructions do not clog the entire pipeline as it did in {{intel|Saltwell}}.  

====Instruction Decode====
In previous generations of microarchitectures, common software code had roughly 5% of instructions split up into micro-ops. In Silvermont this is reduced down to just 1-2%. This reduction translates directly into performance because it eliminates the 3-4 additional cycles of overhead. Silvermont has a second branch predictor that can make more accurate predictions based on previously unknown information (e.g. target address from memory or register) and override the generic predictor. Nevertheless the expense of branch misprediction penalties was also reduced by 3 stages (down to 10 cycles from 13 in {{intel|Saltwell}}).

=== Branch Prediction ===
Silvermont has two branch predictions: one that controls the instruction fetching and a second one that can override the first during the decode stage after gather additional information. The second predictor controls the speculative instruction issuing. For the first predictor, Silvermont uses a [[Branch Target Buffer]] to determine the next fetch address which also includes a 4-entry Return Stack Buffer for calls and returns handling.

== Die ==
8-core {{intel|Avoton}} Die:

[[File:silvermont die (quad-core).png]]

== Cores ==
* {{intel|Tangier}} - SoCs for Smartphones
* {{intel|Valleyview}} - SoCs for Tablets
* {{intel|Avoton}} - SoCs for Microservers
* {{intel|Rangeley}} - SoCs for Embedded Networking

== All Silvermont Chips ==
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<table class="wikitable sortable">
<tr><th colspan="12" style="background:#D6D6FF;">Silvermont Chips</th></tr>
<tr><th colspan="9">Main processor</th><th colspan="3">IGP</th></tr>
<tr><th>Model</th><th>µarch</th><th>Platform</th><th>Core</th><th>Launched</th><th>SDP</th><th>TDP</th><th>Freq</th><th>Max Mem</th><th>Name</th><th>Freq</th><th>Max Freq</th></tr>
{{#ask: [[Category:microprocessor models by intel]] [[microarchitecture::Silvermont]]
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 |?model number
 |?microarchitecture
 |?platform
 |?core name
 |?first launched
 |?sdp
 |?tdp
 |?base frequency
 |?max memory
 |?integrated gpu
 |?integrated gpu base frequency
 |?integrated gpu max frequency
 |format=template
 |template=proc table 2
 |userparam=13
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</table>
codename	Silvermont +
core count	1 +, 2 +, 4 + and 8 +
designer	Intel +
first launched	2013 +
full page name	intel/microarchitectures/silvermont +
instance of	microarchitecture +
instruction set architecture	x86-64 +
manufacturer	Intel +
microarchitecture type	CPU +
name	Silvermont +
phase-out	2015 +
pipeline stages (max)	14 +
pipeline stages (min)	12 +
process	22 nm (0.022 μm, 2.2e-5 mm) +