May 12 th, 2002 Microprocessors

Introduction Motorola controls roughly 40% of the 32-bit embedded processor market ColdFire is the next generation 68K (research on commonly used instructions and addressing modes) Result is a variable length RISC chip  Length varies from 1 to 3 words

Integer Units 16 general purpose 32-bit registers  D0-D7: Data registers Can be used as index registers  A0-A7: Address registers Software stack pointers Index registers Base address registers A7 is used as hardware stack pointer during stacking for subroutine calls and exception handling

Integer Units Cont… 32-bit Program Counter (PC)  For some modes the PC can serve as a pointer for PC relative addressing 8-bit Condition Code Register (CCR)  Status Register’s low order byte. Only potion of the SR available in User Mode

CCR

Floating Point Units 8 64-bit FP data registers (FP0-FP7)  FP data registers are analogous to the integer data registers  Numbers stored in double-precision format All external data, operands, etc are converted to double –precision before storage  A reset or a null-restore sets FP0-FP7 to positive, nonsignaling NANs

FPUs cont… 32-bit FP control register (FPCR)  Next slide has bit information for FPCR 32-bit FP status register (FPSR)  Refer to manual pages 16 and 17 for bit information 32-bit FP instruction address register (FPIAR)

FPUs cont… ColdFire can execute Integer and FP instructions simultaneously  In case of exception, PC value stacked doesn’t may not point to correct instruction  For the FPU instructions that can generate traps, the FPIAR is loaded with the PC address before FPU begins instructions

Optional MAC Module Multiply and Accumulate Module 32-bit MAC status register (MACSR) 32-bit accumulator register (ACC)  Contains the result of MAC operations 32-bit MAC mask register (MASK)  Only the low-order 16-bits are implemented  When loaded, the low-order 16 bits of the operand are loaded into the register. When stored, the upper 16-bits are forced to 1.

Optional EMAC Module Enhanced MAC 32-bit MACSR  Plus 4 indicator bits for product of accumulation overflow (PAV0-PAV3) 4 32-bit accumulators (ACC0-ACC3) 8 8-bit accumulator extensions (ACCext01, ACCext23)  See manual pages 22 and 23

EMAC cont… 32-bit mask register (MASK) Integrated EMAC provides a common set of DSP operations and enhances the Integer multiply instructions. Provides functionality in 3 areas: 1. Faster signed and unsigned integer multiplies 2. New multiply-accumulate operations supporting signed and unsigned operands 3. New miscellaneous register operations

Supervisor Programming Model Used to implement OS functions. All accesses that affect the control features of the ColdFire processors must be made in supervisor mode. 16-bit status register (SR) 32-bit supervisor stack pointer (OTHER_A7) 32-bit vector base register (VBR) 32-bit cache control register (CACR) 32-bit address space ID register (ASID) 2 32-bit data access control registers (ACR0-1) 2 32-bit instruction access control registers (ACR2-3)

continued… 32-bit MMU base address register (MMUBAR) 2 32-bit ROM base address registers (ROMBAR0-1) 2 32-bit RAM base address registers (RAMBAR0-1) 32-bit module base address register (MBAR) Not all registers are implemented on every version of ColdFire (see page 24)

OTHER_A7 This only exists in V4 of ColdFire  In V4, the SSP and SP exist to provide the necessary support for isolation as dictated by the virtual memory management scheme provided by the Memory Management Unit (MMU). if SR[S] = 1 then A7 = Supervisor Stack Pointer other_A7 = User Stack Pointer else A7 = User Stack Pointer other_A7 = Supervisor Stack Pointer

VBR (Vector Base Reg.) Bits 0-19 are set to 0 Bits contains the 1MByte-aligned base address of the exception vector table in memory. CACR (Cache Control Reg.) Controls operation of data and instruction cache memory Bits can enable, freeze, invalidate cache Also can define default cache mode and write-protect fields

ASID (Address Space Ident.) Only the low-order 8 bits are implemented. Each process has it’s own value, and with the 32-bit MMU will create a 40-bit virtual address space.  Extends 4GB addressable space to 1TB

continued… The other registers address how memory is accessed and mapped. See manual pages 26-28

Addressing Modes There is an extensive list of ASM commands that use different addressing modes.  They enable you to do multiple operations and access multiple resources using basic syntax, such as postincrement and predecrement of registers. Too many to discuss here. See manual pages

Marketing Overview 2 Independent decoupled piplelines  4-stage Instruction Fetch Pipeline (IFP)  5-stage Operand Execution Pipeline  FIFO I-buffer is the decoupling mechanism Limited superscalar execution through use of instruction folding Approaches dual-issue performance but at a much lower silicon cost. 2-level branch acceleration mechanisms

Summary This processor specializes in small code and quick execution. Able to extend addressable space well beyond the 4GB virtual memory range Excels in integer manipulation and DSP functions by use of EMAC module, quite common. Lots of details in the compressed code, reference guide is a must have.

References and Links ColdFire Family Programmer's Reference Manual ColdFire V4 General Information Links of Interest