Editing movidius/microarchitectures/shave v2.0

{{movidius title|SHAVE v2.0|arch}}
{{microarchitecture
|atype=Accelerator
|name=SHAVE v2.0
|designer=Movidius
|manufacturer=TSMC
|introduction=2011
|phase-out=2014
|process=65 nm
|type=VLLIW
|isa=SHAVE
|isa 2=SPARC v8
|l1=1 KiB
|l1 per=core
|l2=128 KiB
|l2 per=chip
|l2 desc=2-way set associative
|side cache=8-64 MiB SDRAM
|side cache per=chip
|predecessor=SHAVE v1.0
|predecessor link=movidius/microarchitectures/shave_v1.0
|successor=SHAVE v3.0
|successor link=movidius/microarchitectures/shave_v3.0
}}
'''Streaming Hybrid Architecture Vector Engine v2.0''' ('''SHAVE v2.0''') is an accelerator microarchitecture designed by [[Movidius]] for their vision processors. SHAVE-based products are branded as the {{movidius|Myriad}} family of vision processors.

== History ==
The original SHAVE architecture was designed primarily for the [[hardware acceleration|acceleration]] of game physics. Low demand for expensive physics acceleration in smartphones has forced a re-focus on image and vision processing. Their architecture was versatile enough that it allowed for fairly simple modification to target machine vision processing.

== Process Technology ==
{{main|65 nm lithography process}}
This microarchitecture was designed for [[TSMC]]'s [[65 nm process]].

== Architecture ==
* Hybrid [[RISC]]-[[DSP]]-[[GPU]] [[VLIW]] architecture
* 20 GFLOPS computational power
** 180 MHz
** At 300 mW
* [[Predicated execution]]
* [[Branch delay slots]]
* Tailored to streaming workloads
* 128-bit vector arithmetic
** 8/16/32-bit [[integer]]
** 16/32-bit [[floating point]]
* Full support for sparse data structures (matrix/array, random access)

=== Instruction Set ===
SHAVE supports a mixture of many different types of instructions belonging to a number of different classes of architectures.

* RISC style
** Instruction predication
** Large set of integer operations
* VLIW style
** Parallel functional units controlled by VLIW instructions
** 8/16/32-bit x 1-4 SIMD int
* DSP style
** Zero overhead looping
** Modulo addressing
** Transparent DMA modes
** FFT, Viterbi, etc..
** Parallel comparisons
* GPU style
** Streaming operations
** 16/32-bit FP operations
** Texture management unit

=== Block Diagram ===
==== Entire SoC ====
[[File:shave v2 soc block.svg|800px]]
==== Individual Core ====
[[File:shave v2 block diagram.svg|900px]]

== Overview ==
[[File:shave v2 overview.svg|right|300px]]
Architecturally, SHAVE is organized similar to [[IBM]]'s {{ibm|CBEA|l=arch|CELL}} architecture. There are independent SHAVE cores, with up to eight in this generation may be chained together. Cores benefit from zero penalty from their two neighbors closest, an intrinsic property of architecture that inherently benefits most code. The chip features an [[L2 cache]] that is shared by all the cores as well as an integrated [[DDR2]] [[integrated memory controller|memory controller]] that is connected to an on-package [[known good die|KGD]] [[3d ic|stacked die]] ranging from 8 to 64 [[MiB]] of [[SDRAM]].

A large set of peripherals are attached to the parameter of the chip which communicate with the cores via the [[AXI bus]]. Those peripherals include support for two high-resolution cameras (up to 12 megapixel) at high rate and high-resolution LCD controllers. The various peripherals can be software-multiplexed via the limited number of I/O pins in the package. The overall management controller core is a [[synthesizable]] [[SPARC]] [[V8]] [[LEON3]].

== Core ==
The underlying concept behind the SHAVE core is extracting significant [[data-level parallelism]]. Each SHAVE core is a [[variable-length very long instruction word]] (VLLIW) processor that can operates on native 32-bit [[integer]] and 128-bit [[vector]] values. Each core incorporates a number of different types of [[register files]] as well as a large set of execution units that make use of the multiple register files with a large number of ports in order to operate on a relatively big set of values at once.

Every SHAVE core resides on an independent power island. Although we were not able to verify this, presumably you can enable and disable cores based on your power requirements through software.

=== Register Files ===
There are three register files: Integer Register File (IRF), Scalar Register File (SRF), Vector Register File (VRF).

The SHAVE's integer register file (IRF) has 17 ports in order enable a large set of parallel data operations each cycle. The IRF has 32 entries of 32-bit integers which are predominantly operated on by the IAU and the SAU. In addition to the IRF is the scalar register file (SRF) which has another set of 32 entries of 32-bit integers. The reason for the second register is to allow the SHAVE to do various three-operand operations and generate predicates for the execution units.

The SHAVE core also has a dedicated vector register file (VRF) which contains 32 entries, each 128-bit wide. 

=== Execution Units ===
[[File:shave v2 eus.png|right|400px]]
The three major arithmetic execution units are the vector arithmetic unit (VAU), the scalar arithmetic unit (SAU), and the integer arithmetic unit (IAU).

The '''integer arithmetic unit''' ('''IAU''') performs all arithmetic instructions that operate on 32-bit integer numbers and access the IRF. The '''scalar arithmetic unit''' ('''SAU''') is far more versatile and can perform all [[integer]] (8-32 bit) and [[floating point]] (HP/FP) operations. The '''vector arithmetic unit''' ('''VAU''') supports 128-bit vector operations of all the integer (8-32 bit) and floating point (HP/FP) types. Since those operations can be done at in the same cycle, it's possible to perform combination of the two in order to do various DSP-like operations such as matrix switching.

In addition to those units, there is also a '''compare-move unit''' ('''CMU''') which is used to generate [[predicates]]. This unit can do things such as three comparison operations per 16-bit/32-bit/8bit entry in the vector register file in parallel with the vector operations which can generate predicates for predicated execution. The CMU effectively interfaces with all the register files and is capable of moving data between them.

The '''branch and repeat unit''' ('''BRU''') is another execution unit with the ability to do continuous iterations with zero overhead. This applies to single or multiple VLIW words and can be used for things usch as parameterizable [[finite impulse response]] (FIR) filters, allowing for significant instruction fetch bandwidth reduction. 

Both the CMU and the BRU can work in conjunction with the '''predicated execution unit''' ('''PEU''') and they work with the VAU all in the same cycle, meaning applications such as pixel decision making can be done incredibly fast in the same cycle.

=== Memory Subsystem ===
[[File:shave v2 mem subsys.svg|right|300px]]
Each SHAVE core has two [[load-store units]], each is capable of doing a single 64-bit operation per cycle from the SRAM tile.

Each SHAVE core has a local 128 KiB slice of SRAM the LSU operates on [[Movidius]] calls the  Connection MatriX (CMX) block. The cache is split between [[instruction cache|instruction]] and [[data cache|data]]. The exact amount is software configurable with a granularity of 8 KiB intervals. Each local cache tile is directly linked to two of its closest neighbors (presumably to the cores located to the west and to the east), allowing for zero-penalty accesses from those memory banks as well. For cache tiles located further on do have a slight latency penalty. Movidius noted that most of the software they've tested does almost all of its communication with its neighboring cores, allowing them to take advantage of this.

The entire chip also has a share 128 KiB of L2 cache and a integrated [[DDR2]] [[integrated memory controller|memory controller]] which is connected to an on-package stacked 8-64 MiB of [[SDRAM]].

=== Bandwidth ===
Each of the registers files in the core incorporate a large number of ports. That, along with wide buses allow for very high sustainable throughput to be achieved at very low clock frequencies (180 MHz). 


:[[File:shave v2 block diagram bandwidth.svg|600px]]


{| class="wikitable" style="text-align: center;"
|-
! colspan="10" | Bandwidth
|-
! Parameter !! VRF !! SRF !! IRF !! LSU !! IDC !!  L1 !!  ISB !! L2 !! SDRAM
|-
| Clk || colspan="9" | 180 MHz
|-
| Bytes || 16 || 4 || 4 || 8 || 16 || 8 || 16  || 16 || 4 
|-
| Ports || 12 || 12 || 17 || 2 || 1 || 1 || 2 || 1 || 2
|-
| Bandwidth || 34.56 || 8.64 || 12.24 || 2.88 || 2.88 || 1.44 || 5.76 || 2.88 ||  1.44
|-
| SHAVE cores || colspan="7" | 8 || colspan="2" | &nbsp;
|-
| Total BW || 276.48 ||  69.12 ||  97.92 || 23.04 || 23.04 || 11.52 || 46.08
|-
| Total || colspan="7" | 547.2 || 2.88 || 1.44
|}

=== Sparse Data Acceleration ===
[[File:movidius shave v2.0 sparse data example.png|right|400px]]
The SHAVE cores support sparse data operations with the [[load-store unit]] using eight 4-bit fields to generate the address.

:[[File:movidius shave v2.0 sparse data support.png|700px]]

== Inter-core communication ==
This architecture does not have support for hardware synchronization primitives, however it does have a light communication system.

Each of the SHAVE cores has a small arbitration messaging [[queue]] consisting of four entries of 64-bit words which is only accessibly (read-wise) from that core. Each SHAVE core can send a message to any other core. When this happens the message is pushed onto that core's queue. If that core's queue is full, the sender will stall. This allows for very efficient SHAVE-SHAVE synchronization and communication without using any shared memory techniques.

It's worth noting that the control/management [[LEON3]] [[SPARC]] core does not have access to this communication system.

== Performance claims ==
Movidius reported very high performance numbers for their chip. Fabricated on a [[65 nm process]] and operating at 180 MHz and consuming 300 milliwatt, the full chip is capable of doing 300 GOPS or just over 1 TOPS per watt for 8-bit arithmetic for their integer arithmetic operations and 60 GOPS for 8-bit vector operations.

:[[File:shave v2 performance claims.png|600px]]

== Package ==
[[File:myriad 1 bga.png|right|200px]]
Movidius packaged those chips in an 8x8 mm [[BGA]] package with 225 [[solder ball|balls]]. The die is then bumped on top of a custom [[FR-4 substrate]]. The SDRAM is then [[wire bond|wire bond]] on top of the Myriad die.

:[[File:myriad package diagram.svg|600px]]

== Floorplan ==
The full chip consists of just two macros - the CMX block and the SHAVE core block. The whole die was place and routed with those two marcros with the rest routed flat at the end. 

:[[File:shave v2 floorplan.svg|400px]]

== Myriad Die ==
* [[TSMC]]'s [[65 nm process|65nm Low Power (65LP) process]]
* < 64 mm² die size


:[[File:myriad 1 (shave v2.0) die shot.png|class=wikichip_ogimage|600px]]


:[[File:myriad 1 (shave v2.0) die shot (annotated).png|600px]]

== All SHAVE v2.0 Chips ==
<!-- 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 tc4">
{{comp table header|main|5:List of SHAVE v2.0-based Processors}}
{{comp table header|main|5:Main processor}}
{{comp table header|cols|Price|Launched|Cores|%Frequency}}
{{#ask: [[Category:microprocessor models by movidius]] [[microarchitecture::SHAVE v2.0]]
 |?full page name
 |?model number
 |?release price
 |?first launched
 |?core count
 |?base frequency#MHz
 |format=template
 |template=proc table 3
 |userparam=6
 |mainlabel=-
}}
{{comp table count|ask=[[Category:microprocessor models by movidius]] [[microarchitecture::SHAVE v2.0]]}}
</table>
{{comp table end}}

== References ==
* Some information was obtained directly from Movidius
* HotChips 23 (HC23), 2011
codename	SHAVE v2.0 +
designer	Movidius +
first launched	2011 +
full page name	movidius/microarchitectures/shave v2.0 +
instance of	microarchitecture +
instruction set architecture	SHAVE + and SPARC v8 +
manufacturer	TSMC +
name	SHAVE v2.0 +
phase-out	2014 +
process	65 nm (0.065 μm, 6.5e-5 mm) +