CS 152
Computer Architecture and Engineering
Lecture 1 – Single Cycle Design
2014-1-21
John Lazzaro
(not a prof - “John” is always OK)
TA: Eric Love
www-inst.eecs.berkeley.edu/~cs152/
Play:
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Today’s lecture plan ...
Class Outline.
What we’ll be doing this semester.
Short Break.
Single-cycle processor design.
Preliminaries ... prep for Thursday.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Nvidia
Tegra K1
Tech Talk
5:30 PM
this
Thursday
in the Woz.
Tegra K1
remixes the
Kepler GPU
architecture
for lowpower
SOCs.
Nvidia
Tegra K1
This class
prepares
you to be on
a team like
the one at
Nvidia that
designed
this chip.
Nvidia
Tegra K1
This is true
even if your
goal is to be
in the group
that designs
circuits ...
... or writes
software ...
for the chip.
Lecture
topics
GPU
architecture:
Apr 15/17.
Dynamic
scheduling:
Apr 1/3, 8/10.
Memory
System:
(February)
Array of 192
CUDA cores
in the
Kepler GPU
ARM A15 CPU Cores (4+1)
Hierarchical Memory System
And other topics
What do we get to do?
Timeline
For 9 weeks, lectures and labs only.
Lab 1: Pipelines:
Lab 2: Caches:
Midterm March 18: Complete HW1 and take Midterm 1
Lab 3: Dynamically-Scheduled CPU Design:
Midterm II May 1:
Complete HW2 and take Midterm 2
About the labs
Rocket, a RISC-V (“risk five”) chip project
Professor
Krste Asanovic
directs ASPIRE
(microprocessor design
research project).
CS 152 uses ASPIRE
software tools and
CPU designs.
ASPIRE graduate
students take turns
with TA duties.
RISC-V: a new instruction set architecture (ISA)
Extensive software support: gcc port, disassemblers, etc.
Chisel: Professor Bachrach’s hardware description language
Labs will use Chisel simulators of RISC-V CPU designs
Open-source ... on the web ...
Warning: It’s tricky
to compile ...
Each lab has two parts
Not ‘team’
labs - you
work alone.
Directed portion
Teaches you how to use the tools.
Helps you understand the material.
Not doing well puts you in ‘C’ grade territory.
Open-ended portion
Define a project and work on it for several weeks.
“High bar” for an ‘A’ grade (about 10% of class).
“Solid, competent work” gets you a ‘B’ grade.
Falls out of EECS 2.7-3.1
upper-division GPA guidelines.
About exams:
Two mid-terms and no final.
Mid-term start time TBD
About homeworks:
Discussion sections
Go to the section
you can make.
Focused on labs.
TA: Eric Love (ASPIRE graduate student).
Essential for doing well in the labs.
John does Q&A for lecture materials, midterms, hw.
What constitutes ‘cheating’ on labs?
And more generally ...
Required text ... 5th edition only
On reserve in library.
See class website for readings for each lecture ...
Recommended text ...
On reserve in library.
Any edition is fine ... whatever you used for 61C.
Administriva, Part I
Piazza is our all-to-all communication media.
Send John email if he hasn’t contacted you about it.
Class website is our archival media.
Lecture slides, labs, due dates ... add ‘/sp14’ to URL.
Tools run on EECS instructional machines.
Get the account form from Eric in discussion.
Laptop/tablet/smartphone in class.
Fine for note taking and class-related activities.
Every lecture will have a short break in the middle.
Please wait till the break for heavy-duty multitasking.
Administriva Rain Checks
Expect updates soon on the following items:
Course grading
Breakdown between mid-terms and labs,
more details on how we will grade the labs.
Office hours
For Eric and John.
Deadlines policies.
Our late policies for labs, and procedures
if you can’t make it to one of the mid-terms.
Wait list.
We hope we can let everyone in, but we don’t know for
sure yet. If you are planning to drop, email John.
Break
Play:
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Instruction Set Architecture
The labs
will use
the RISC-V
ISA ...
CS 152: Single-Cycle Design
Lectures
examples
will mostly
use the
MIPS ISA.
UC Regents Spring 2014 © UCB
New successful instruction sets are rare
software
instruction set
hardware
Implementors suffer with original sins of
ISAs, to support the installed base of
software.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Instruction Sets: A Thin Interface
Syntax: ADD $8 $9 $10
Semantics: $8 = $9 + $10
Application (iTunes)
Compiler
Software
Hardware
Assembler
Operating
System
(Mac OS X)
Processor Memory I/O system
Instruction Set
Architecture
Datapath & Control
Digital Design
Circuit Design
Transistors
“R-Format”
Fieldsize: 6 bits 5 bits 5 bits 5 bits 5 bits
6 bits
Bitfield: opcode
rs
rt
rd shamt funct
Binary:000000 01001 01010 01000 00000 100000
In Hexadecimal: 012A4020
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Hardware implements semantics ...
Syntax: ADD $8 $9 $10
Instruction
Fetch
Instruction
Decode
Operand
Fetch
Execute
Result
Store
Next
Instruction
Semantics: $8 = $9 + $10
Fetch next inst from memory:012A4020
opcode rs
rt
rd shamt funct
Decode fields to get : ADD $8 $9 $10
“Retrieve” register values: $9 $10
Add $9 to $10
Place this sum in $8
Prepare to fetch instruction that
follows the ADD in the program.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
ADD
syntax &
semantics,
as seen in
the MIPS
ISA
document.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Memory Instructions: LW $1,32($2)
Instruction
Fetch
Instruction
Decode
Operand
Fetch
Execute
Result
Store
Next
Instruction
Fetch the load inst from memory
opcode
rs
rt
offset
“I-Format”
Decode fields to get : LW $1, 32($2)
“Retrieve” register value: $2
Compute memory address: 32 + $2
Load memory address contents into: $1
Prepare to fetch instr that follows
the LW in the program. Depending on
load semantics, new $1 is visible to
that instr, or not until the following
instr (”delayed loads”).
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
LW
syntax &
semantics,
as seen in
the MIPS
ISA
document.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Branch Instructions: BEQ $1,$2,25
Instruction
Fetch
Instruction
Decode
Operand
Fetch
Execute
Result
Store
Next
Instruction
Fetch branch inst from memory
opcode
rs
rt
offset
“I-Format”
Decode fields to get: BEQ $1, $2, 25
“Retrieve” register values: $1, $2
Compute if we take branch: $1 == $2 ?
ALWAYS prepare to fetch instr that
follows the BEQ in the program
(”delayed branch”). IF we take branch,
the instr we fetch AFTER that
instruction is PC + 4 + 100.
CS 152: Single-Cycle Design
PC == “Program
UC Regents Spring 2014 © UCB
BEQ
syntax &
semantics,
as seen in
the MIPS
ISA
document.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
define: The Architect’s Contract
To the program, it appears that
instructions execute in the correct
order defined by the ISA.
As each instruction completes, the
machine state (regs, mem) appears to
the program to obey the ISA.
What the machine actually does is up
to the hardware designers, as long
as the contract is kept.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Single Cycle CPU Design
Preliminaries
...
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
Single cycle data paths: Assumptions
Processor uses
synchronous logic
design (a “clock”).
f
T
1 MHz
1 μs
10 MHz
100 ns
100 MHz
10 ns
1 GHz
1 ns
D
All state elements act
like positive edgetriggered flip flops.
CS 152: Single-Cycle Design
Q
Reset ?
clk
UC Regents Spring 2014 © UCB
Review: Edge-Triggered D Flip Flops
D
Q
Value of D is sampled on positive clock
edge.
Q outputs sampled value for rest of
cycle.
CLK
D
Q
This abstraction is sufficient for the 2014 CS 152!
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
If you are a circuit designer ...
Not required for 2014 CS 152 ...
D
Q
A flip-flop “samples” right before
the edge, and then “holds” value.
Sampling
circuit
Holds
value
16 Transistors: Makes an SRAM look compact!
What do we get for the 10 extra transistors?
Clocked logic semantics.
CS 250 L3: Timing
UC Regents Fall 2013 © UCB
If you are a CS 150 veteran ...
Not required for 2014 CS 152 ...
D
Q
Value of D is sampled on positive clock
edge.
Q outputs sampled value for rest of
cycle.
module ff(D, Q, CLK);
CLK
input D, CLK;
output Q;
reg Q;
always @ (posedge CLK)
Q <= D;
endmodule
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB
define: Single-cycle datapath
All instructions
execute in a single
cycle of the clock
(positive edge to
positive edge)
Advantage: a great
way to learn CPUs.
CS 152: Single-Cycle Design
Drawbacks: unrealistic
hardware assumptions,
slow clock period
UC Regents Spring 2014 © UCB
Thursday:
Complete single-cycle ...
and maybe get to other
listed topics.
CS 152: Single-Cycle Design
UC Regents Spring 2014 © UCB