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Stack Mode Initialization/Reset TMS320C55x
Monideep Mukherjee ABSTRACT This document contains information examples initialize several stack modes that available TMS320C55x DSP. Contents Data System Stacks Stack Configurations Dual 16-Bit Stack With Fast Return Dual 16-Bit Stack With Slow Return 32-Bit Stack With Slow Return Stack Mode Initialization Booting From External Using Soft Reset With Vector Table Initialize Stack List Figures Figure Figure Stack Pointers Stack Mode Initialization C5000 Hardware Applications
Data System Stacks
TMS320C55x includes 16-bit software stacks known user data) stack system stack. user stack normal stack where user push values. user stack includes stack pointer (SP) that contains lower bits return address calls interrupts. also holds values anything pushed onto stack. system stack exists compatibility with TMS320C54x series processors. system stack incorporates system stack pointer (SSP) that contains upper bits return address calls interrupts. Once user sets system stack, left alone because does contain user-pushed data. Figure shows relationship between system user stack pointers.
22-16 15-0
XSSP
Legend: High bits XSSP (this modified during normal stack operations) 23-Bit Extended Data Stack Pointer XSSP 23-Bit Extended System Stack Pointer
Figure Stack Pointers
TMS320C55x TMS320C54x trademarks Texas Instruments. Other trademarks property their respective owners.
SPRA378
Stack Configurations
TMS320C55x provides three possible stack configurations with slow fast returns. difference between fast-return slow-return process saves restores value internal registers: program counter (PC) loop context register. holds 24-bit address bytes code being decoded unit. When performs interrupt call, current value (return address) stored, then loaded with start address interrupt service routine called routine. When returns from routine, return address transferred back that interrupted program sequence continue before. slow-return process, return address loop context stored stacks memory. When returns from subroutine, speed which these values restored dependent speed memory accesses. fast-return process, return address saved return address register (RETA) loop context saved control-flow context register (CFCT). RETA CFCT registers read written pair with 32-bit load store instructions.
Dual 16-Bit Stack With Fast Return
this mode, data system stack independent. When access made data stack, stack pointer (SP) modified, system stack pointer (SSP) not. RETA CFCT registers used implement fast return. This mode optimal stack mode operation: saves both cycles memory. Note that nested calls, RETA CFCT both saved.
Dual 16-Bit Stack With Slow Return
this mode, data stack system stack independent; when data stack accessed, stack pointer modified, system stack pointer not. Note that RETA CFCT registers used. This mode slower than Dual 16-Bit Stack With Fast Return mode; however, gives added advantage simplifying stack unwinding because only memory involved, registers used.
32-Bit Stack With Slow Return
data stack system stack single 32-bit stack; when data stack accessed, modified same increment. RETA CFCT used. Note that modified directly, automatically updated. user must keep pointers aligned. This configuration default stack mode supports C54x compatibility.
Stack Mode Initialization
stack mode during power reset; therefore, bits reset vector determine what mode operation stack performs. Texas Instruments (TI) bootloader used, code, default, sets C54x compatibility, which means 32-Bit Stack With Slow Return mode used.
C54x trademark Texas Instruments.
Stack Mode Initialization/Reset TMS320C55x
SPRA378
stack mode different ways:
booting from booting from vector table with mode Reset Vector location initiated with software reset
Booting From External
system boots from external ROM, then 32-bit reset vector location have following formats:
Dual 16-Bit Stack With Fast Return Reset Vector xxxx xxxx xxxx xxxx xxxx xxxx xxxx Bits must zero Bits contain 24-bit start address reset interrupt service routine Bits [30,31,27 don't cares
Dual 16-Bit Stack With Slow Return Reset Vector xxxx xxxx xxxx xxxx xxxx xxxx xxxx must must Bits contain 24-bit start address reset interrupt service routine Bits [30,31,27 don't cares
32-Bit Stack With Slow Return Reset Vector xxxx xxxx xxxx xxxx xxxx xxxx xxxx must must Bits contain 24-bit start address reset interrupt service routine Bits [30,31,27 don't cares
Please note that reset vector address refers location that automatically goes when software hardware reset occurs. reset interrupt service routine least bits reset vector where begins execution reset interrupt service routine.
Using Soft Reset With Vector Table Initialize Stack
second initialize stack mode reset vector, vectors.asm file.
;Vectors.asm .sect "vectors" rsv: .ivec ISR_start_location, STACK_MODE
where STACK_MODE
C54X_STK: USE_RETA: NO_RETA: 32-bit stack (default) 16-bit stack using RETA 16-bit stack with RETA
Figure Stack Mode Initialization
Stack Mode Initialization/Reset TMS320C55x
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