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Bonnell µarch
General Info
Arch Type	CPU
Designer	Intel
Manufacturer	Intel
Introduction	2008
Phase-out	2011
Process	45 nm
Core Configs	1, 2
Pipeline
Type	Superscalar
Speculative	No
Reg Renaming	No
Stages	16-19
Instructions
ISA	IA-32, x86-64
Extensions	MOVBE, MMX, SSE, SSE2, SSE3, SSSE3
Cache
L1I Cache	32 KiB/Core 8-way set associative
L1D Cache	24 KiB/Core 6-way set associative
L2 Cache	512 KiB/Core 8-way set associative
Cores
Core Names	Silverthorne, Diamondville, Lincroft, Pineview, Tunnel Creek, Stellarton, Sodaville, Groveland
Succession
Saltwell

Bonnell was a microarchitecture for Intel's 45 nm ultra-low power microprocessors first introduced in 2008 for their then-new Atom family. Bonnell, which was named after the highest point in Austin - Mount Bonnell, was Intel's first x86-compatible microarchitecture designed to target the ultra-low power market.

Bonnell (project Silverthorne then) was designed by a then-new low-power design team Intel created at their Texas Development Center in Austin in 2004 along with a new chipset (Poulsbo) design team. The design team was led by Elinora Yoeli. While Yoeli previously worked at her native country, Bonnell was a US design and was unconnected to any of Intel's projects worked on by the Israel Design Center in Haifa. Previously Yoeli led the Israeli team in the development of Pentium M.

Codenames

Chipset	Platform	PHC	Core	Target
Poulsbo	Menlow		Silverthorne	MIDs
Poulsbo	Menlow		Diamondville	Nettops
	Moorestown	Langwell	Lincroft	MIDs
	Pine Trail	Tiger Point	Pineview	Nettops
	Queens Bay	Topcliff	Tunnel Creek	Embedded
	Queens Bay	Topcliff	Stellarton	Embedded + Altera FPGA
			Sodaville	CE
			Groveland	CE

Generation successor

First Generation		Second Generation
Silverthorne	→	Lincroft
Diamondville	→	Pineview
		Tunnel Creek
		Stellarton
		Sodaville
		Groveland

Release Dates

Bonnell was first announced on April 2nd 2008 during the Intel Developers Forum in Shanghai.

Process Technology

45 nm Manufacturing Fabs
Fab	Location
D1D	Hillsboro, Oregon
Fab 32	Chandler, Arizona
Fab 28	Kiryat Gat, Israel

Bonell is designed to be manufactured using a 45 nm process. Intel's 45 nm process is the first high-volume manufacturing process to introduce High-k + metal gate transistors.

	Bonnell
	45 nm
Gate Pitch	180 nm
Interconnect Pitch	160 nm
SRAM bit cell (HD)​	0.346 µm²
SRAM bit cell (LP)​	0.382 µm²

Compiler support

Compiler	Arch-Specific	Arch-Favorable
GCC	-march=bonnell	-mtune=bonnell
LLVM	-march=bonnell	-mtune=bonnell
Visual Studio	/arch:SSE3

Architecture

Bonnell features a brand new architecture not based on any previous Intel design. The architecture was specifically designed for ultra-mobile PCs (UMPCs), mobile internet devices (MID), and other embedded devices. Bonnell's primary goals were:

1. Reduce power consumption,
2. while staying fully x86-compatible,
3. at acceptable performance

Performance/Power new rule: +1% performance for at most +1% power consumption.

Architecture

• Strictly ultra-low power
  • 90%+ lower power than 90 nm Pentium M
• 45 nm process, 9 metal layers, CMOS
• 500 mW to 2 W TDP
  • Average 220 mW
  • Idle under 80 mW
• 533 MT/s dual mode (GTL & CMOS) FSB
• In-order
• 2-issue decode
• Simple 2-way SMT
• Instruction Queue of 32 entries (16 entries/thread)
• FP Register File (per thread)
• Integer Register File (per thread)
• Private L1 cache for each core
• Shared L2 cache for the entire chip

The number of functional units were kept to minimum to cut on power consumption.

• 2 address generation units (AGUs)
• 2 Integer ALUs (1 for jumps, 1 for shifts)
• 2 FP ALUs (1 adder, 1 for others)
• No Integer multiplier & divider (shared with FP ALU instead)

Memory Hierarchy

• Cache
  • Hardware prefetchers
  • C6 cache
    • 10.5 KiB array to hold the architectural state during deep power down state
  • L1 Instruction Cache
    • 36 KiB
      • 32 KiB Instruction + 4 KiB Boundary Mark
      • 8-way set associative
    • 1 read and 1 write port
    • 8 transistors (instead of 6) to reduce voltage
  • L1 Data Cache
    • 24 KiB
      • 6-way set associative
    • 1 read and 1 write port
    • 8 transistors (instead of 6) to reduce voltage
    • Per core
  • L2 Cache:
    • 512 KiB 8-way set associative
    • ECC support
    • Shrinkable from 512 KiB to 128 KiB (2-way)
    • 64-bit cache line
    • Per core
  • L3 Cache:
    • No level 3 cache
  • RAM
    • Maximum of 2 GiB, 4 GiB, and 8 GiB

Note that the L1 cache for data and instructions were originally both 32 KiB (8-way), however due to power restrictions, the L1d$ was later reduced to 24 KiB.

• TLB
  • ITLB
    • 32-entry
    • fully associative
  • DTLB
    • 4 KiB PAges
      • 64-entry TLB
        • 4-way set associative
      • 16-entry micro-TLB
        • fully associative
        • duplicated for each thread
      • 16-entry PDE cache
        • fully associative
    • Large Pages
      • 8 entries, 4-way set associative

Overview

Bonnell's architecture shares very little in common with other Intel designs. To achieve the strict ultra-low power objects, Bonnell features a very slimmed own design discarding many high-performance techniques used by Intel's high-performance architectures such as aggressive speculative execution, out-of-order execution, and µop transformation.

Part of the design requirement was that Bonnell retain full x86 compatibility, up to the latest extension - at the 10th of the power consumption of the Pentium M. This meant any software is now 100% compatible but it forced engineers to deal with all the baggage the architecture brought along. The decision to offer full compatibility brought its own set of benefits such as access to the largest software code base in the world, including the ability to run any other x86 operating system unmodified. At the same time it forced the design team to resort to other means of reducing power.

Up to Bonnell, all of Intel's existing architectures put very low priority on power efficiency (note that this has significantly changed since the introduction of Sandy Bridge). High-performance, high-throughput, complex designs are simply inadequate for the kind of power goals required out of Bonnell, even if they were trimmed down. It was decided that Bonnel would be designed from the scratch with power goals in mind. For those reasons Bonnell resembles the P5 microarchitecture.

Pipeline

Much like the original P5 microarchitecture, Bonnell consists of an in-order dual-issue pipeline. The pipeline is shown below. Note the pipeline is duplicated for dual-issue execution.

Unlike P5, which only had 5 stages, Bonnell has 16 to 19 stages pipeline. The longer pipeline allows a more evenly spreading of heat across the chip with more units. This also allows a higher clock rate.

Front End

Bonnell's front end is very simple when compared to Intel's high-performance architectures. Out-of-order execution (OoOE) that is found ubiquitously in all HPC architectures was rejected. Bonnell's power and area constraints simply couldn't allow for the complex logic needed to support that capability. The Instruction Fetch consists of 3 stages capable going through up to 8 bytes per cycle (with a lower amount if SMT is enabled). Like fetch, the Instruction Decode is also 3 stages capable of decording instructions with up to 3 prefixes each cycle (considerably longer for more complex instructions).

Bonnell is a departure from all modern x86 architectures with respect to decoding (including those developed by AMD and VIA and every Intel architecture since P6). Whereas modern architectures transform complex x86 instructions into a more easily digestible µop form, Bonnell does almost no such transformations. The pipeline is tailored to execute regular x86 instructions as single atomic operations consisting of a single destination register and up to three source-registers (typical load-operate-store format). Most instructions actually correspond very closely to the original x86 instructions. This design choice results in lower complexity but at the cost of performance reduction. Bonnell has two identical decoders capable of decoding complex x86 instructions. Being variable length instruction architecture introduces an additional layer of complexity. To assist the decoders, Bonnell implements predecoders that determine instruction boundaries and mark them using a single-bit marker. Two cycles are allocated for predecoding as well as L1 storage. Boundary marks are also stored in the L1 eliminating the need to preform needlessly redundant predecoding. Repeated operations are retrieved pre-marked eliminating two cycles. Bonnel has a 36 KiB L1 instruction cache consisting of 32 KiB instruction cache and 4 KiB instruction boundary mark cache. All instructions (coming from both cache or predecode) must undergo full decode. It's worthwhile noting that Intel states Bonnell is a 16-stage pipeline because for the most part, after a cache hit you'll have 16 stages. This is also true in some cases where the processor can simultaneously decode the next instruction. However, in the cases where you get a miss, it will cost 3 additional stages to catch up and locate the boundary for that instruction for a total of 19 stages.

Some x86 instructions are simply too complex to handle directly. Those selected few get diverted into the microcode sequencer for decoding producing much more sane RISCish instructions at the cost of 2 additional cycles. Intel estimates that only 5% of common software require instructions to be split up. The inability to execute things out-of-order eliminates lots of optimization opportunities at this stage. One thing Bonnell can do is lockstep instructions that can be execute simultaneously such as in the case of instructions that performance a memory access along an arithmetic operation. In those instances Bonnell will issue the instruction as if it were two separate instructions executing simultaneously.

Because Bonnell has support for Hyper-Threading, Intel's brand name for their own simultaneous multithreading technology, a number of modifications had to be done. The prefetch buffer and the instruction queue have been duplicated for each thread.

Branch predictor

No aggressive speculative execution is done in Bonnell, however it does implements a light-weight branch predictor consisting of a two-level adaptive predictor with a 12-bit global history table. The pattern history table has 4096 entries and is competitively shared between threads. The branch buffer target has 128 entries (4-way by 32 sets). While unconditional jumps are not recorded in the table, always-taken and never-taken jumps do.

The branch-misprediction penalty is 11 to 13 cycles. Some of the rare or complex x86 instructions will detour into a microcode sequencer for decoding, necessitating two additional clock cycles. Additionally there is a roughly 7 cycle penalty for correctly predicted branches but no target can be predicted because of a missing branch target buffer (BTB) entry. Bonnell return stack buffer is 8-entry deep.

Back End

Each cycle two instructions are dispatched in-order. The scheduler can take a pair of instructions from a single thread or across threads. Bonnell in-order back-end resembles a traditional early 90s design featuring a dual ALU, a dual FPU and a dual AGU. Similarly to the front-end, in order to accommodate simultaneous multithreading, the Bonnell design team chose to duplicate both the floating-point and integer register files. The duplication of the register files allows Bonnell to perform context switching on each stage by maintaining duplicate states for each thread. The decision to duplicate this logic directly results in more transistors and larger area of the silicon. Overall implementing SMT still required less power and less die area than the other heavyweight alternatives (i.e., out-of-order and larger superscaler).

In the further pursuit of power saving specialized execution units were minimized as much as possible. Bonnell uses the same logic that is used for SIMD integer multiplier and floating point divider to execute scalar integer multiply and integer divider respectively.

Multithreading

Bonnell supports Intel's Hyper-Threading, their marketing term for their own implementation of simultaneous multithreading. The notion of implementing simultaneous multithreading on such a low-power architecture might seem unusual at first. In fact, it's one of only a handful of ultra-low power architectures to support such feature. Intel justified this design choice by demonstrating that performance enjoys an uplift of anywhere from 30% to 50% while worsening power consumption by up to 20% (with an average of 30% performance increase for 15% more power). The toll on the die area was a mere 8%.

In the front-end, the prefetch buffer and the instruction queue have been duplicated for each thread, everything else is competitively shared between the threads. In the back-end, only the integer and floating register files are duplicated, everything else is competitively shared as well. Note that both threads compete over the L1 instruction and data caches as well as the L2 and the TLBs with the exception of a 16-entry micro-TLB that's duplicated for each thread.

Die

• 45 nm process
• 9 metal layers
• 47,000,000 transistors
• 3.1 mm x 7.8 mm
• 24.2 mm² die size

• BIC - Bus Interface Cluster
• MEC - Memory Cluster Execution & L1d$
• FPC - FP/SIMD execution Cluster
• IEC - Integer Execution Cluster
• FEC - Front-End Cluster & L1i$
• FSB - Front Side Bus

Cores

First Generation

First generation of Bonnell-based microprocessors introduced 2 cores: Silverthorne for ultra-mobile PCs and mobile Internet devices (MIDs) and Diamondville for ultra cheap notebooks and desktops.

Silverthorne

Main article: Silverthorne

Silverthorne was the codename for a series of Mobile Internet Devices (MIDs) introduced in 2008. These processors had 1 core and 2 threads with a FSB operating at 400 MHz-533 MHz.

Diamondville

Main article: Diamondville

Diamondville was the codename for the series of ultra cheap notebooks and desktops introduced in 2008. Diamondville is very much a soldered-on-motherboard derivative of Silverthorne with faster FSB (operating at 533 MHz - 667 MHz). The dual-core version is an MCM (Multi Chip Module) Silverthorne variant.

Second Generation

First generation of Bonnell-based microprocessors while being low power had to work with the older 90 nm process 945GSE chipset and 82801GBM I/O controller with a TDP of almost 9.5 watts - almost 4 times that of the processor itself. Second generation Bonnell-based microprocessors aimed to address this issue by integrating a memory controller and GPU on-chip. This drastically reduced power consumption and cost.

Lincroft

Main article: Lincroft

Lincroft is the codename for Bonnell-based Silverthorne's successor. Lincroft integrates on-die the graphics and memory controller.

Pineview

Main article: Pineview

Pineview was the codename for second generate Bonnell-based processors which integrated a memory controller, Direct Media Interface (DMI) link, and the GMA 3150 GPU. Pineview is the successor for Diamondville, targeting the same ultra cheap desktops, nettops and netbooks.

Tunnel Creek

Main article: Tunnel Creek

Tunnel Creek was the codename for a series of MPUs for embedded applications.

Stellarton

Main article: Stellarton

Stellarton was the codename for a series of MPUs for embedded applications. Stellarton is the Tunnel Creek core packaged with an Altera FPGA.

Sodaville

Main article: Sodaville

Sodaville is the codename for a series of consumer electronics system on a chip (e.g. set-top box).

Groveland

Main article: Groveland

Groveland is the codename for a series of consumer electronics MPUs (e.g. smart TVs).

All Bonnell Chips

Bonnell Chips
CPU								IGP
Model	µarch	Platform	Core	Launched	SDP	Freq	Max Mem	Name	Freq	Max Freq
230	Bonnell	Nettop 2008	Diamondville	3 June 2008		1,599.99 MHz 1.6 GHz 1,599,990 kHz	8,192 MiB 8,388,608 KiB 8,589,934,592 B 8 GiB 0.00781 TiB
330	Bonnell	Nettop 2008	Diamondville	21 September 2008		1,599.99 MHz 1.6 GHz 1,599,990 kHz	8,192 MiB 8,388,608 KiB 8,589,934,592 B 8 GiB 0.00781 TiB
N270	Bonnell	Nettop 2008	Diamondville	3 June 2008		1,599.99 MHz 1.6 GHz 1,599,990 kHz	8,192 MiB 8,388,608 KiB 8,589,934,592 B 8 GiB 0.00781 TiB
N280	Bonnell	Nettop 2008	Diamondville	7 February 2009		1,666.66 MHz 1.667 GHz 1,666,660 kHz	8,192 MiB 8,388,608 KiB 8,589,934,592 B 8 GiB 0.00781 TiB
Z500	Bonnell	Menlow	Silverthorne	2 April 2008	0.96 W 960 mW 0.00129 hp 9.6e-4 kW	800 MHz 0.8 GHz 800,000 kHz
Z510	Bonnell	Menlow	Silverthorne	2 April 2008	0.96 W 960 mW 0.00129 hp 9.6e-4 kW	1,100 MHz 1.1 GHz 1,100,000 kHz
Z510P	Bonnell	Menlow	Silverthorne	2 March 2009		1,100 MHz 1.1 GHz 1,100,000 kHz
Z510PT	Bonnell	Menlow	Silverthorne	2 March 2009		1,100 MHz 1.1 GHz 1,100,000 kHz
Z515	Bonnell	Menlow	Silverthorne	8 April 2009		1,200 MHz 1.2 GHz 1,200,000 kHz
Z520	Bonnell	Menlow	Silverthorne	2 April 2008	0.96 W 960 mW 0.00129 hp 9.6e-4 kW	1,333.33 MHz 1.333 GHz 1,333,330 kHz
Z520PT	Bonnell	Menlow	Silverthorne	2 March 2009		1,333.33 MHz 1.333 GHz 1,333,330 kHz
Z530	Bonnell	Menlow	Silverthorne	2 April 2008		1,599.99 MHz 1.6 GHz 1,599,990 kHz
Z530P	Bonnell	Menlow	Silverthorne	2 March 2009		1,599.99 MHz 1.6 GHz 1,599,990 kHz
Z540	Bonnell	Menlow	Silverthorne	2 April 2008	0.96 W 960 mW 0.00129 hp 9.6e-4 kW	1,866.66 MHz 1.867 GHz 1,866,660 kHz
Z550	Bonnell	Menlow	Silverthorne	8 April 2009		1,999.99 MHz 2 GHz 1,999,990 kHz
Z560	Bonnell	Menlow	Silverthorne	June 2010		2,133.33 MHz 2.133 GHz 2,133,330 kHz
Z600	Bonnell	Moorestown	Lincroft	4 May 2010		800 MHz 0.8 GHz 800,000 kHz	1,024 MiB 1,048,576 KiB 1,073,741,824 B 1 GiB 9.765625e-4 TiB	PowerVR SGX535	200 MHz 0.2 GHz 200,000 KHz
Z605	Bonnell	Moorestown	Lincroft	4 May 2010		1,000 MHz 1 GHz 1,000,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz
Z610	Bonnell	Moorestown	Lincroft	4 May 2010		800 MHz 0.8 GHz 800,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz
Z612	Bonnell	Moorestown	Lincroft	4 May 2010		900 MHz 0.9 GHz 900,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz
Z615	Bonnell	Moorestown	Lincroft	4 May 2010		1,200 MHz 1.2 GHz 1,200,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz
Z620	Bonnell	Moorestown	Lincroft	4 May 2010		900 MHz 0.9 GHz 900,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz
Z625	Bonnell	Moorestown	Lincroft	4 May 2010		1,500 MHz 1.5 GHz 1,500,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz
Z650	Bonnell	Oak Trail	Lincroft	11 April 2011		1,200 MHz 1.2 GHz 1,200,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz
Z670	Bonnell	Oak Trail	Lincroft	11 April 2011		1,500 MHz 1.5 GHz 1,500,000 kHz	2,048 MiB 2,097,152 KiB 2,147,483,648 B 2 GiB 0.00195 TiB	PowerVR SGX535	400 MHz 0.4 GHz 400,000 KHz

References

• Some information was obtained directly from Intel
• Gerosa, Gianfranco, et al. "A sub-2 W low power IA processor for mobile internet devices in 45 nm high-k metal gate CMOS." IEEE Journal of Solid-State Circuits 44.1 (2009): 73-82.
• Gerosa, Gianfranco, et al. "A sub-1W to 2W low-power IA processor for mobile internet devices and ultra-mobile PCs in 45nm hi-κ metal gate CMOS." Solid-State Circuits Conference, 2008. ISSCC 2008. Digest of Technical Papers. IEEE International. IEEE, 2008.