Programable Logic Devices In the 1970s programmable logic circuits called programmable logic device (PLD) was introduced. They are based on a structure with an AND- OR array that makes it easy to implement SOP expression William Sandqvist [email protected] PLD structure x 1 x 2 x n Input buffers and inverters x 1 x 1 x n x n P1 AND plane OR plane Pk f 1 f m William Sandqvist [email protected] Programmable Logic Array (PLA) x1 x2 x3 Both AND and OR arrays are OR P1 plane programmable P2 P3 P4 AND plane f f William Sandqvist [email protected] Programmable Array Logic (PAL) x1 x2 x3 Only the AND array is programmable P1 f1 P2 P3 f2 P4 AND plane William Sandqvist [email protected] Register output In the earlier PLD circuits there were • combinatorial outputs • register outputs (output with a flip-flop) For each circuit there were a fixed number of combinational and register outputs To increase flexibility the macrocell where you could choose if an output would be a combinatorial or a register output was introduced. William Sandqvist [email protected] Macrocels ia a PLD Select Enable f 1 Flip-flop D Q With a programmable multiplexer one can Clock select the type of output To AND plane William Sandqvist [email protected] PAL William Sandqvist [email protected] Programing of PLDs William Sandqvist [email protected] Complex PLDs (CPLD) PLD were quite small (PALCE 22V10 had 10 flip-flops) For bigger programmable circuits a structure consisting of several PLD-like block was developed. William Sandqvist [email protected] CPLD (MAX) William Sandqvist [email protected] CPLD structure I/O block block I/O PAL-like PAL-like block block I/O block block I/O Interconnection wires I/O block block I/O PAL-like PAL-like block block I/O block block I/O William Sandqvist [email protected] Programing with JTAG Modern CPLDs (and FPGAs) can be programmed by downloading programming information via a cable Download will usually use a standard port: JTAG-port William Sandqvist [email protected] JTAG programing You can program the chips when they are soldered to the circuit board - from inside the programmer you (a) CPLD in a Quad Flat Pack (QFP) package can select which chip you want to program with the To computer JTAG connector. Pri nted ci rcui t board (b) JTAG programming William Sandqvist [email protected] FPGA chips CPLD:s are based on the AND-OR array, and it becomes difficult to make really large circuits FPGA (Field Programmable Gate Array) circuits using a different concept based on logical blocks William Sandqvist [email protected] FPGA-structure William Sandqvist [email protected] LUT-LookUp-Table Programmable 0/1 A LUT with n 1 cells inputs can realize all combinational 0/1 0 functions with n 1 inputs. f The usual size in 0/1 0 1 an FPGA is n=4 0/1 0 x2 x1 Two-input LUT William Sandqvist [email protected] Ex. LUT for XOR-gate 0 1 xxf21 1 0 110 1 011 f 0 1 1 101 000 0 0 x2 x1 Two-input LUT William Sandqvist [email protected] Logic block in FPGA A logic block of an FPGA consists of a LUT, a flip- flop, and a mux to select register output. Select Out Flip-flop In 1 In 2 LUT D Q In 3 Clock William Sandqvist [email protected] Interconnexion matrix in FPGA x 3 f • Blue cross: connection is x programmed 1 x 1 0 x 2 0 • Black cross: 0 1 f 1 f 2 x x 0 x 0 connection is not 2 2 1 3 0 programmed f 1 0 1 f 1 f 2 1 William Sandqvist [email protected] DE2 University Board Cyclone II EP2C35 FPGA – Datorteknik- course William Sandqvist [email protected] Cyclone II logic element William Sandqvist [email protected] Cyclone II Family (3) Total Number of 18x18 Multipliers DE2 William Sandqvist [email protected] Stratix III Family DE3 Board William Sandqvist [email protected] Multiple processors on an FPGA • Nios II is a so-called 'soft- processor' (32-bit) which can be implemented on an Nios II Altera FPGA • Today's FPGAs are so large that multiple Nios II processors can fit on a single FPGA chip Very powerful multiprocessor systems can be created on an FPGA! William Sandqvist [email protected] ASIC • An ASIC (Application Specific Integrated Circuit) is a circuit that is madi in a semiconductor factory • In a full custom integrated circuit you in principle tailors the whole circuit • In an ASIC have certain work steps already been made to reduce design time and cost William Sandqvist [email protected] ASIC, gate array In an Gate Array the gates (or transistors) are allready on the silicon. William Sandqvist [email protected] ASIC, gate array f 1 One only creates x 1 links between inputs, gates, and outputs x 2 x 3 William Sandqvist [email protected] Comparison ASIC, FPGA Initial Cost Cost per part Performance Fabrication Time FPGA Low High Low Short Gate Array (ASIC) Standard Cell High Low High Long (ASIC) William Sandqvist [email protected] Design Trade-Offs Design Time Full Custom Standard Cell Gate Array Programmable Logic Microprocessor Performance William Sandqvist [email protected] William Sandqvist [email protected] Sekvenskretsar med VHDL State NEXT STATE OUTPUT DECODER STATE REGISTER DECODER Input- Output- signals signals Clk Moore-machine William Sandqvist [email protected] Model a State Machine in VHDL • In a Moore-machine we have three blocks – Next-state-decoder – Output-decoder – State-register • These blocks execute in parallel William Sandqvist [email protected] Quickie Question … which logic gate corresponds to the following VHDL code William Sandqvist [email protected] Quickie Question … which logic gate corresponds to the following VHDL code William Sandqvist [email protected] Quickie Question … which logic gate corresponds to the following VHDL code William Sandqvist [email protected] Quickie Question … which logic gate corresponds to the following VHDL code William Sandqvist [email protected] Processes in VHDL • An architecture in VHDL can consist of several processes • Processes are executed in parallel • A process is written as a sequential program William Sandqvist [email protected] Moore-machine processes • For a Moore-machine, we can create three processes – Next-state-decoder – Output-decoder – State-register William Sandqvist [email protected] Internal signals • Moore-machine contains internal signals – Next state – Present state • Theese signals are declared in the architecture-description William Sandqvist [email protected] The vending machine in VHDL We use bottle vending machine (system control) from last lecture as a concrete VHDL example COIN COIN_PRESENT DROP DROP BOTTLE RECEIVER GT_1_EURO DROP_READY EQ_1_EURO SYSTEM CONTROL LT_1_EURO DEC_ACC RETURN_10_CENT ACCUMU- COIN RETURN LATOR CLR_ACC CHANGER_READY William Sandqvist [email protected] Vending machine entity ENTITY Vending_Machine IS COIN_PRESENT DROP PORT ( GT_1_EURO DROP_READY -- Inputs coin_present : IN std_logic; EQ_1_EURO SYSTEM CONTROL gt_1_euro : IN std_logic; LT_1_EURO eq_1_euro : IN std_logic; lt_1_euro : IN std_logic; DEC_ACC RETURN_10_CENT drop_ready : IN std_logic; CLR_ACC CHANGER_READY changer_ready : IN std_logic; Reset_n reset_n : IN std_logic; clk : IN std_logic; Clk -- Outputs dec_acc : OUT std_logic; clr_acc : OUT std_logic; Clk and Reset (active low) is drop : OUT std_logic; also needed! return_10_cent : OUT std_logic); END Vending_Machine; William Sandqvist [email protected] Vending machine architecture • The architecture describes the function of the vending machine • We define – internal signals for present and next state – three processes for next-state- decoder, output-decoder and state- register William Sandqvist [email protected] State diagram (a) Wait for coin input (b) Register the coin (c) Coin is registered (3 cases) (d) Drop bottle (e) Reset sum (f) Return 10 Cent (g) Decrement sum with 10 Cent William Sandqvist [email protected] Internal signals • We need to create a data type for the internal signal • Since we describe the states we use an enumeration type with values a,b,c,d,e,f,g • We declare a variable for the current state (current_state) and one for next state (next_state) ARCHITECTURE Moore_FSM OF Vending_Machine IS TYPE state_type IS (a, b, c, d, e, f, g); SIGNAL current_state, next_state : state_type; BEGIN -- Moore_FSM … William Sandqvist [email protected] We want to keep our "clever” state encoding • If we do not specify the encoding state then the synthesis tool chooses the coding. • We can force it to a specific encoding with attributes (NOTE Attributes are dependent on synthesis tool and thus not portable!) ARCHITECTURE Moore_FSM OF Vending_Machine IS TYPE state_type IS (a, b, c, d, e, f, g); -- We can use state encoding according to BV 8.4.6 -- to enforce a particular encoding (for Quartus) ATTRIBUTE enum_encoding : string; ATTRIBUTE enum_encoding OF state_type : TYPE IS "000 001 011 110 111 100 101"; SIGNAL current_state, next_state : state_type; BEGIN -- Moore_FSM … William Sandqvist [email protected] Block schematic DA A COIN_PRESENT D LT_I_EURO Clk DROP EQ_I_EURO RETURN_I0_CENT GT_I_EURO DB B DROP_READY Next State D Output Decoder Clk Decoder CHANGER_READY CLR_ACC DEC_ACC A DC C B D C Clk • Signals A,B,C describes present state • Signals DA, DB, DC describes next state William Sandqvist [email protected] Quickie Question … which statemachine corresponds to the VHDL code William Sandqvist [email protected] Quickie Question … which statemachine corresponds to the VHDL code William Sandqvist [email protected] Next-State-Decoder • Next-State-Decoder describes as a process • Sensitivity list contains all input signals that 'activates' the process William Sandqvist [email protected] Next-State-Decoder • Usually the sensitivity list contains all the inputs to the process NEXTSTATE : PROCESS (current_state, coin_present, gt_1_euro, eq_1_euro, lt_1_euro, drop_ready, changer_ready)