Embedded Systems phần 3 ppt
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22
Network Systems Architecture
Processor Capabilities
Can we make a useful embedded system
out of just a processor?
Memory?
I/O?
DMA transfers, networking, …
Power?
Most of this can be provided with a
system-on-a-chip
23
Network Systems Architecture
AMCC PowerPC 440GX
500 – 800 MHz
256kB on-chip SRAM
I/O support
PCI-X
DDR SDRAM memory controller
4 Ethernet MACs (2 gigabit, 2 10/100)
Hardware Assist Units
Accelerate and offload responsibility from CPU core
DMA Engine
TCP/IP Offload Engine
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Network Systems Architecture
PowerPC 440GX
25
Network Systems Architecture
PowerPC 440GX + Board
AMCC
PowerPC
440GX
AvBus
JTAG
RISCWatch
Flash
(32MB)
DDR SDRAM
256MB w/ECC
200-pin SODIMM
2x Ethernet PHY
10/100/1000
PCI-X
64-bit / 133 MHz
RS232
LEDs
Switches
26
Network Systems Architecture
Software Limits
How is software constrained by the PowerPC
440GX?
DMA engine limited to 256 byte transfers
TOE has specific interface
On-chip SRAM fixed at 256kB
Any other constraints?
A stand-alone processor might not solve all
problems for all customers
Not cost-effective for IBM (or Intel, AMD, …) to
integrate all possible functionality on all chips
27
Network Systems Architecture
Embedded Systems
Spectrum of design options
Run all tasks in software on embedded
processor
Offload a few tasks to hardware
Run most tasks in hardware, with high-level
control in software
28
Network Systems Architecture
Routers
Why would I build a router entirely in software?
Flexibility
Speed of implementation
Why would I use more custom hardware?
Efficiency - Power/space
Cost - Mass production?
Performance - Can’t route 10Gbps in software with a
single processor
Scale - General-purpose components too small
(not enough I/O ports, on-chip buffers, etc )
How could I build a 50 port 10Gbps router using only
software running on commodity PCs? Switch design must be
in custom hardware
29
Network Systems Architecture
Embedded Systems - Hardware Design
30
Network Systems Architecture
Hardware Design
How do I approach a new project involving
embedded systems?
Design first!
Pick right components for the job
Processors, custom hardware, FPGAs, …
Design tools, debugging tools, …
What questions should an engineer ask
about the project to guide the design?
Example: “What is my project budget?”
31
Network Systems Architecture
Design Questions
What do I need to interface
with?
What constraints do those
devices place on me?
Real-time control?
High data rates?
Continuous data stream?
What computation does my
device need to do?
Can these tasks be done in
parallel?
What is the minimum level of
reliability required?
What are my power
restrictions?
What is my project budget?
($$)
When must my project reach
the marketplace?
What is the production run of
the device? (tens? thousands?
millions?)
Can I buy a fast/expensive
chip and write “good-enough”
software?
Do I need to design an ASIC
that can be mass-produced
cheaply?
… and more!
