ECOM 4311 Digital Systems Design

Transcription

1 ECOM4311 Digital Systems Design ECOM 4311 Digital Systems Design Eng. Monther busultan Computer Engineering Dept. Islamic University of Gaza genda 1. History of Digital Design pproach 2. HDLs 3. Design bstraction 4. Modern Design Steps 5. Implementation Options (FPGs) Page 1 Page 2 In the beginning More recently 1970's - designers used Paper/Pencil & oolean Equations to create schematics - impractical in large designs 1980's - schematic based designs using electronic editors - this enabled Copy/Paste & Hierarchy - Design-reuse was enabled which increased design sizes mid 80's - HDL's became more common (created mid 80's) - Text-based Compilers (C, PSCL) could be adapted to perform digital simulation - Larger Designs could be described using text Design 1990's - Synthesis became practical due to increase in computational power of computers Synthesis - The creation of circuitry from a functional description ex) "Functional Description of MU" if (Sel = 0) = else = Synthesis Sel Still separate Physical Implementation Page 3 Page 4 Real Power 1990's - Now engineers had a power combination "HDL" if (Sel = 0) = else = bstraction Engineers could now stay at a higher level of abstraction and rely on the tools to 1) Simulate. 2) Synthesize the circuitry. - This allows larger systems to be described/designed in the same time. "" "Synthesis" Sel - Since HW is expensive to build, using the tools to reduce prototyping was the next step. Page 5 Page 6 1

2 Timing Verification - Let the tool "Verify" timing - Less time spent prepping design for a prototyping run Functional HDL Synthesis Technology Mapping VHDL V = Very High Speed Integrated Circuit (VHSIC) H = Hardware D = Description L = Language Place/Route (extract RC's) - Originally Designed by IM, TI, Intermetrics (all sponsored by US DoD) - Original Intent was to Document ehavior (instead of writing system manuals) Match? Post Implementation - Original Intent was NOT synthesis, that came later Fab - was a given, since the designs were already in text and we had text compilers (C,.) Page 7 Page 8 - In 1987, IEEE published the "VHDL Standard" - High Impedance - IEEE = First formal version of VHDL - Strong "Data Typing" - each signal/variable is typed (bit, bit_vector, real, integer) - assignments between different types NOT allowed - Did not handle multi-valued logic - it is how circuits behave, strong drivers will control the bus when everyone is High-Z - When nobody is driving the bus, the bus is High-Z - So for true behavior, VHDL has to model High-Z - VHDL's built in types (bit and bit_vector) can only be 0 or 1, these don't cut it. - Weak/Strong - usses have multiple drivers but some are weaker than others. - We should model these too. Page 9 Page 10 - VHDL allows users to come up with their own data types. - Since the world needed multi-valued logic, everyone started creating their own add-on packages. - this created a lot of confusion when multiple vendors worked together (i.e., Fab Shop and Designer) - In 1993, IEEE published an Upgrade - IEEE added support for Multi-Valued Logic through the "STD_LOGIC" package - better syntax consistency - Other package standards that were added to VHDL = "Real and Complex Data Types" = "Signed and Unsigned Data Types" - The rev of VHDL in 2003 (1076.3) is the most commonly used release. - The most recent update is in 2008 (VHDL 4.0) which was approved by IEEE in 2009 ( ). - Every time there is a need for a data type, industry will start to create add-ons, then IEEE will create a standard to reduce confusion. Page 11 Page 12 2

3 Design bstraction VHDL Usage t What level can we design? fundamental motivation to use VHDL is that VHDL is a standard, technology/vendor independent language, and is therefore portable and reusable. The two main immediate applications of VHDL are in: The field of Programmable Logic Devices (CPLDs, FPGs). The field of SICs. Once the VHDL code has been written, it can be used either to implement the circuit in: a programmable device (from ltera, ilinx, tmel, etc.) or can be submitted to a foundry for fabrication of an SIC chip. Currently, many complex commercial chips (microcontrollers, for example) are designed using such an approach. Page 13 Page 14 Design bstraction What does abstraction give us? - The higher in abstraction we go, the more complex & larger the system becomes - ut, we let go over the details of how it performs (speed, fine tuning) - There are engineering jobs at each level Designing Large Circuits - this is the ideal process Digital Design Flow What does VHDL model? - System : Chip : Register : Gate - VHDL let's us describe systems in two ways: 1) Structural (text netlist) 2) ehavioral (requires synthesis) Page 15 Page 16 Digital Design Flow FPG's Designing Large Circuits - this is reality What is an FPG Field Programmable Gate rray n FPG uses Re-urable Logic locks - we set the uration bits of this block to set its oolean logic function - the uration is a Truth Table (or Look Up Table) of functionality 000 NOT() 001 NOT() 010 OR 011 NOR 100 ND 101 NND 110 OR 111 NOR Page 17 Page 18 3

4 FPG's FPG's FOR 4-INPUT EVEN PRITY GENERTOR DDRESS Input put s = Look Up Tables - we can program the s to be whatever type of gate is needed by the design - there are a finite number of s within a given FPG (also called "resources") The s are ured into an RRY on the silicon - rray of 's = rray of Gates = Gate rray Page 19 Page 20 FPG's FPG's Programmable Interconnect - there are programmable interconnect switches that connect the s - We start with a Gate Level Schematic of our design (from synthesis) - The FPG s are ured to implement Gates Page 21 Page 22 FPG's FPG's - The interconnect switches are then programmed to implement the net connections - The and Interconnect uration is volatile (i.e., it goes away when power is removed) - Since the programming is done by the user after fabrication, we call it "Field Programmable C INV ND INV OR - That is where Field Programmable Gate rray comes from. C INV ND INV OR Page 23 Page 24 4

5 FPG's FPG's dding More Functionality - FPG manufacturer's quickly learned that Flip-Flops would be useful Switch box - They put a DFF next to a 4-Input to form a "Configurable Logic lock" (CL) CL CL CL CL Page 25 Page 26 FPG's dding Even More Functionality - To Improve performance, common logic functions were "hard coded" on the silicon - lock RM - dders / Multipliers - Global Clock uffers - even Microprocessors! - PowerPC 32/64 bits RISC - Microlaze* 32 bits RISC - NIOS II* 32 bits RISC - Picolaze* 8 bits RISC What else can we program? FPG's - Which Pins to use on the package - Clock - GPIOs - Reset - - What logic levels - CMOS_33, CMOS25, etc * This is provided as a synthesizable component that can be Implemented on the logic fabric. Page 27 Page 28 FPG's FPG Overview Programming the FPG The Real World - FPG - EEPROM - we can program the FPG directly - volatile nature means if we remove power, we'll lose program - we can download our code into an on-board EEProm - Upon power up, the EEProm will program the FPG - FPG's historically (mid 90's) have been too expensive for deployment in commercial designs - SICs have become very expensive and FPG's have become more powerful - s a result, it is now cost effective to use FPG's in designs - Learning how an FPG operates and how to get performance out of them is a highly sought after engineer skill! Page 29 Page 30 5