Embedded Systems: Hardware Computer Processor Basics ISA (Instruction Set Architecture) RTL (Register Transfer Language) Main reference: Peckol, Chapter 1 Fig

ISA: Categories: busing structure data types, size, representation instructions length, format(s) operator, # operands, address mode instruction types arithmetic / logical data movement, including I/O control function and procedure calls: stack?

fig_01_01 Basic components Common bus structure: address, data, control fig_01_03

fig_01_05 Some processor options (note firmware) DSP (A/D, D/A; high speed—video, audio, images 2. Microcontroller-based system Fig components integrated into one unit) 1. Microprocessor- based system fig_01_06 fig_01_07

fig_01_08 DATA: DATA TYPES NUMERIC --Unsigned integer --Signed integer (2’s complement, sign-magnitude, fixed point, etc.) --Floating point: 3 components: sign exponent mantissa NONNUMERIC --address --character

Numeric data 1.Range is always limited. Number of digits of resolution is size of fractional part. Example: in 4 numeric bits: Number of bits in fractionrange 0 (integer)0-15 1: xxx.x0-7.5 (fractions 0, ½) 2: xx.xx (fractions, 0, ¼, ½, ¾) 3: x.xxx (fractions, 0, 1/8, ¼, 3/8, ½, 5/8, ¾, 7/8)

fig_01_09 Most base 10 fractions cannot be represented exactly in binary: Example: how to represent 2.x in 4 bits, with 2 bits of resolution? Choices: 2.0, 2.25, 2.5, 2.75,  2.0 or  2.0 or  2.0 or 2.25 or 2.5 truncation rounding down rounding up r roundingtruncation Error range for n bits of resolution: Truncation: -2 -n < E truncation < 0 Rounding: - ½ 2 -n < E rounding < ½ 2 -n Computation: which is easier to compute?

Error propagation in arithmetic: Examples: Consider two numbers whose true values are N 1 and N 2 and whose values in the computing system are N 1E and N 2E Addition: errors add:N 1E = N 1 + E 1 N 2E = N 2 + E 2 N 1E + N 2E = (N 1 + E 1 ) + (N 2 + E 2 ) = N 1 + N 2 + E 1 + E 2 Multiplication: error : N 1E * N 2E = (N 1 + E 1 ) * (N 1 + E 2 ) = (N 1 N 2 ) + (N 2 * E 1 + N 1 * E 2 ) + (E 1 * E 2 ) term 1term 2 Note that if term 2 is neglected then error depends on size of N 1 and N 2

fig_01_10 Another example (pp of text): measuring power dissipated in resistor R in the following circuit: Suppose E = 100 VDC +/- 1%, I = 10A +/- 1%, R = 10 ohms +/- 1%. 3 methods of calculating power dissipated, neglecting lower order error terms: a. E1 = (100V +/- 1%) * (10A +/- 1%) =  b. I 2 R = (10A +/- 1%) * (10A +/- 1%) * (10 ohms +/- 1%) = 997  1003 c. E3 = (100 V +/- 1%)*(100 V +/- 1%) / (10 ohms +/- 1%) =  Which should we use? “optimistic”: a “middle-of-the-road”: average of a,b,c “safest”: c

Instructions—ISA level Instruction coding: HLL (high level language, C, C++, e.g.)  assembly language (ISA)  machine language (can work at any level; high level allows faster but less efficient coding) IEEE Standard —IEEE standard for microprocessor assembly language—used for examples in text

Instruction coding: Fields: operator, operands (type of addressing) Example: 32 bits 3 bits: opcode 2 bits: address mode (e.g. direct, indirect, indexed, immediate) 27 bits: for addressing operand (s) Expanding opcode (example): xxxx…xxx: 2 operands 1110xxx…xxx: 1 operand 1111xxx…xxx: no operand (e.g., HALT) operator addr mode operand(s)

fig_01_13 fig_01_14 fig_01_15 Example instruction formats

Instructions Instruction types: arithmetic / logical data movement control Arithmetic / logical instructions: operator; number of operands; arity (unary, binary, three-operand, …) Examples: x = -x negation, assignment x = yassignment x = x + yaddition, assignment z = x + yaddition, assignment

fig_01_42 Typical ALU and registers

fig_01_43 Common ALU functions Cannot be affected by interrupt

fig_01_44 Common ALU functions (continued)

fig_01_45 Common ALU functions (continued) Question: what is a minimal set of ALU instructions?

fig_01_16 Data movement instructions: source / destination

fig_01_17 Common data movement instructions Question: how can you implement XCH without using a temporary variable?

fig_01_12 Addressing modes: Immediate: MOVE A, #BH; Direct:MOVE OPR1, OPR2; Indirect:MOVE OPR1, *myVarPtr; MOVE *OPR1, *OPR1; MOVE *OPR1, **yPtr; Register direct:MOVE Reg1, Reg2; Register indirect:MOVE Reg1, *Reg2; Indexed (loops):MOVE Reg1, OPR2[REG2]; PC relative (loops,e.g.; offset can be negative): ADD PC, [Reg1]; Example: what is the difference between Y, *Y, **Y Indirect addressing— myVarPtr holds address or myVar

fig_01_21 Addressing examples:

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Control instructions Control can be: sequential (default) loop (pre or posttest) branch: go to conditional (if, if-else,, case, branch on condition) procedure or function call [interrupt or exception] change in control flow, e.g., I/O device ready Unusual event, e.g., overflow or undefined instruction

fig_01_29 Branch instructions Typical condition codes Typical branch instructions: fig_01_30

fig_01_31 Example of conditional statements: C / assembly language: fig_01_32

fig_01_34 Looping: example fig_01_35

fig_01_36 fig_01_37 Function or procedure call: Must store return address, pass information back and forth What are standard parameter passing methods?

fig_01_39 Stack: common way to handle procedure / function calls Q: what are two alternative methods for handling function / procedure calls? Which methods facilitate recursion?

fig_01_40 Function call: example: fig_01_41

Question: can you design a “general-purpose computer” with a 3-bit opcode?

fig_01_46 Different viewpoint: RTL: register-transfer language level

fig_01_49 Register behavior: Read / Write; Serial / Parallel fig_01_50 fig_01_51

fig_01_52 RTL VIEW fig_01_53

fig_01_54 fig_01_55 Instruction execution cycle Q: Where is this step implemented?

fig_01_57 Multiple levels--examples

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table_01_03

Project 1: build a simple processor (bit-slice design) Von Neumann architecture Only one general purpose register (accumulator) Supports direct, indirect, and indexed addressing Small instruction set, 2 formats ( or 111) Primitive I/O (via accumulator) Word addressable, 18-bit word Addressing direct, indirect, indexed by A or by B I/O to and from accumulator or a special- purpose register ALU M MA IRACCFMDIAIBPC ABUS OBUS BBUS ALU OUTPUT M: memory MA: memory address register MD: memory data register IR: instruction register AC: accumulator CF: carry flag IA, IB: index registers (13 bit) PC: program counter Instruction format: Op code (3) Addr Mode (2) Address (13) Functionality: 2's complement add, subtract, multiply, and divide, and, or, not jumps (conditional and unconditional), simple subroutine call and return Interrupts I/O Minimal hardware resources  high degree of functionality