Real-Time Embedded Systems

 Microprocessor Characteristics  Von Neumann and Harvard architectures  I/O Addressing  Endianness  Memory organization of some classic microprocessors ◦ PIC18F8720 ◦ Intel 8086 ◦ Intel Pentium ◦ Arm

X. Fan: Real-Time Embedded Systems 2 Some microprocessors used in embedded systems

3 Microprocessor Architectures

 Von Neumann Architecture ◦ Data and instructions (executable code) are stored in the same address space. ◦ The processor interfaces to memory through a single set of address/data buses.  Harvard Architecture ◦ Data and instructions (executable code) are stored in separate address spaces. ◦ There are two sets of address/data buses between processor and memory.  Complex Instruction Set Computer (CISC) ◦ runs “complex instructions“ where a single instruction may execute several low-level operations  Reduced Instruction Set Computer (RISC) ◦ runs compact, uniform instructions where the amount of work any single instruction accomplishes is reduced.

4 Other Stuff

 Processing Width ◦ Width ◦ Word  I/O Addressing ◦ Special instruction vs memory mapped  Reset Vector ◦ Intell – high end of address space ◦ PIC/ and Motorolla (Frescale, NXT….) low ◦ Arm definable ◦ Why put it on end or the other?

X. Fan: Real-Time Embedded Systems 5 Endianness

6 Endianness  Whether integers are presented from left to right or right to left ◦ Little-endian: the least significant byte stored at the lowest memory address ◦ Big-endian: the most significant byte stored at the lowest memory address

7 System Convention

 Be internally consistent ◦ Endianness ◦ Data formats ◦ Protocols ◦ Units  Do conversion ASAP and ALAP ◦ On and off the wire

X. Fan: Real-Time Embedded Systems 8 PIC18F8720

9 PIC18F8720: Memory organization

10 PIC18F8720: EMI Operating mode: Word Write Mode  This mode allows instruction fetches and table reads from, and table writes to, all forms of 16-bit (word-wide) external memories.

Embedded Real-Time Systems 11 PIC18F8720: Word Write Mode: Timing Diagram

Embedded Real-Time Systems 12 PIC18F8720: EMI Operating mode: Byte Select Mode

 This mode allows instruction fetches and table reads from, and table writes to, external memories with byte selection capability.

Embedded Real-Time Systems 13 PIC18F8720: Byte Select Mode: Timing Diagram

Embedded Real-Time Systems 14 PIC18F8720: Byte Select Mode: Memory Mappings

15 PIC18F8720: Byte Select Mode: Problem 3.3

 Which chip would be written to if in the first cycle the instruction is “TBLWT 12h to address 1A6B4Ch" and in the second cycle the instruction is “TBLWT 8Ah to address 1A6B4Dh?  Would the data 12h and 8Ah be stored on the memory chip correctly? Explain why.

Embedded Real-Time Systems 16 PIC18F8720: Byte Write Mode

 This mode allows table reads from, and table writes to, 8- bit-wide external memories.

Embedded Real-Time Systems 17 PIC18F8720: Byte Write Mode: Timing Diagram

Embedded Real-Time Systems 18 Intel 8086

CLK provides the basic timing for the processor and bus controller. Each bus cycle (read, write, or interrupt acknowledge) consists of at least four clock cycles, which are referred to as T1, T2, T3 and T4.

19 Memory Organization: internal segmentation

 There are four 16-bit segment registers ◦ CS for Code Segment, ◦ DS for Data Segment, ◦ ES for Extra data Segment, and ◦ SS for Stack Segment.  All memory references are of form [segment:offset], relative to the base address contained in the corresponding segment register.  Given a pair [segment:offset], a 20-bit external address is produced by

20 Intel 8086 Memory IO Mappings

21 Intel 8086 Memory Mapping

22 Intel 8086: Chip Select

23 Shift Register: 74LS164

1 2 3 4 5

Embedded Real-Time Systems 24 Intel 8086 Wait State Generator

25 Intel Pentium

26 Intel Pentium: Bus State Transition

X. Fan: Real-Time Embedded Systems 27 Intel Pentium Memory Mapping

X. Fan: Real-Time Embedded Systems 28 Arm926EJ-S

X. Fan: Real-Time Embedded Systems 29 Arm926EJ-S: memory mapping (8-bit memory)

X. Fan: Real-Time Embedded Systems 30 Arm926EJ-S: memory mapping (32-bit memory)

X. Fan: Real-Time Embedded Systems 31