![12
TM 12
39v10 The ARM Architecture
When the processor is executing in ARM state:
All instructions are 32 bits wide
All instructions must be word aligned
Therefore the pc value is stored in bits [31:2] with bits [1:0] undefined (as
instruction cannot be halfword or byte aligned).
When the processor is executing in Thumb state:
All instructions are 16 bits wide
All instructions must be halfword aligned
Therefore the pc value is stored in bits [31:1] with bit [0] undefined (as
instruction cannot be byte aligned).
When the processor is executing in Jazelle state:
All instructions are 8 bits wide
Processor performs a word access to read 4 instructions at once
Program Counter (r15)](https://image.slidesharecdn.com/arm-intro-230111140901-db5b9345/85/arm-intro-ppt-12-320.jpg)
![22
TM 22
39v10 The ARM Architecture
To allow larger constants to be loaded, the assembler offers a pseudo-
instruction:
LDR rd, =const
This will either:
Produce a MOV or MVN instruction to generate the value (if possible).
or
Generate a LDR instruction with a PC-relative address to read the constant
from a literal pool (Constant data area embedded in the code).
For example
LDR r0,=0xFF => MOV r0,#0xFF
LDR r0,=0x55555555 => LDR r0,[PC,#Imm12]
…
…
DCD 0x55555555
This is the recommended way of loading constants into a register
Loading 32 bit constants](https://image.slidesharecdn.com/arm-intro-230111140901-db5b9345/85/arm-intro-ppt-22-320.jpg)
![23
TM 23
39v10 The ARM Architecture
Multiply
Syntax:
MUL{<cond>}{S} Rd, Rm, Rs Rd = Rm * Rs
MLA{<cond>}{S} Rd,Rm,Rs,Rn Rd = (Rm * Rs) + Rn
[U|S]MULL{<cond>}{S} RdLo, RdHi, Rm, Rs RdHi,RdLo := Rm*Rs
[U|S]MLAL{<cond>}{S} RdLo, RdHi, Rm, Rs RdHi,RdLo := (Rm*Rs)+RdHi,RdLo
Cycle time
Basic MUL instruction
2-5 cycles on ARM7TDMI
1-3 cycles on StrongARM/XScale
2 cycles on ARM9E/ARM102xE
+1 cycle for ARM9TDMI (over ARM7TDMI)
+1 cycle for accumulate (not on 9E though result delay is one cycle longer)
+1 cycle for “long”
Above are “general rules” - refer to the TRM for the core you are using
for the exact details](https://image.slidesharecdn.com/arm-intro-230111140901-db5b9345/85/arm-intro-ppt-23-320.jpg)
![25
TM 25
39v10 The ARM Architecture
Address accessed
Address accessed by LDR/STR is specified by a base register plus an
offset
For word and unsigned byte accesses, offset can be
An unsigned 12-bit immediate value (ie 0 - 4095 bytes).
LDR r0,[r1,#8]
A register, optionally shifted by an immediate value
LDR r0,[r1,r2]
LDR r0,[r1,r2,LSL#2]
This can be either added or subtracted from the base register:
LDR r0,[r1,#-8]
LDR r0,[r1,-r2]
LDR r0,[r1,-r2,LSL#2]
For halfword and signed halfword / byte, offset can be:
An unsigned 8 bit immediate value (ie 0-255 bytes).
A register (unshifted).
Choice of pre-indexed or post-indexed addressing](https://image.slidesharecdn.com/arm-intro-230111140901-db5b9345/85/arm-intro-ppt-25-320.jpg)
![26
TM 26
39v10 The ARM Architecture
0x5
0x5
r1
0x200
Base
Register 0x200
r0
0x5
Source
Register
for STR
Offset
12 0x20c
r1
0x200
Original
Base
Register
0x200
r0
0x5
Source
Register
for STR
Offset
12 0x20c
r1
0x20c
Updated
Base
Register
Auto-update form: STR r0,[r1,#12]!
Pre or Post Indexed Addressing?
Pre-indexed: STR r0,[r1,#12]
Post-indexed: STR r0,[r1],#12](https://image.slidesharecdn.com/arm-intro-230111140901-db5b9345/85/arm-intro-ppt-26-320.jpg)
![28
TM 28
39v10 The ARM Architecture
PSR Transfer Instructions
MRS and MSR allow contents of CPSR / SPSR to be transferred to / from
a general purpose register.
Syntax:
MRS{<cond>} Rd,<psr> ; Rd = <psr>
MSR{<cond>} <psr[_fields]>,Rm ; <psr[_fields]> = Rm
where
<psr> = CPSR or SPSR
[_fields] = any combination of ‘fsxc’
Also an immediate form
MSR{<cond>} <psr_fields>,#Immediate
In User Mode, all bits can be read but only the condition flags (_f) can be
written.
27
31
N Z C V Q
28 6
7
I F T mode
16
23 8
15 5 4 0
24
f s x c
U n d e f i n e d
J](https://image.slidesharecdn.com/arm-intro-230111140901-db5b9345/85/arm-intro-ppt-28-320.jpg)
arm-intro.ppt
- 1. 1 TM T H E A R C H I T E C T U R E F O R T H E D I G I T A L W O R L D The ARM Architecture
- 2. 2 TM 2 39v10 The ARM Architecture Agenda Introduction to ARM Ltd Programmers Model Instruction Set System Design Development Tools
- 3. 3 TM 3 39v10 The ARM Architecture ARM Ltd Founded in November 1990 Spun out of Acorn Computers Designs the ARM range of RISC processor cores Licenses ARM core designs to semiconductor partners who fabricate and sell to their customers. ARM does not fabricate silicon itself Also develop technologies to assist with the design-in of the ARM architecture Software tools, boards, debug hardware, application software, bus architectures, peripherals etc
- 4. 4 TM 4 39v10 The ARM Architecture ARM Partnership Model
- 5. 5 TM 5 39v10 The ARM Architecture ARM Powered Products
- 6. 6 TM 6 39v10 The ARM Architecture Agenda Introduction to ARM Ltd Programmers Model Instruction Sets System Design Development Tools
- 7. 7 TM 7 39v10 The ARM Architecture Data Sizes and Instruction Sets The ARM is a 32-bit architecture. When used in relation to the ARM: Byte means 8 bits Halfword means 16 bits (two bytes) Word means 32 bits (four bytes) Most ARM’s implement two instruction sets 32-bit ARM Instruction Set 16-bit Thumb Instruction Set Jazelle cores can also execute Java bytecode
- 8. 8 TM 8 39v10 The ARM Architecture Processor Modes The ARM has seven basic operating modes: User : unprivileged mode under which most tasks run FIQ : entered when a high priority (fast) interrupt is raised IRQ : entered when a low priority (normal) interrupt is raised Supervisor : entered on reset and when a Software Interrupt instruction is executed Abort : used to handle memory access violations Undef : used to handle undefined instructions System : privileged mode using the same registers as user mode
- 9. 9 TM 9 39v10 The ARM Architecture r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 (sp) r14 (lr) r15 (pc) cpsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r8 r9 r10 r11 r12 r13 (sp) r14 (lr) spsr FIQ IRQ SVC Undef Abort User Mode r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 (sp) r14 (lr) r15 (pc) cpsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r8 r9 r10 r11 r12 r13 (sp) r14 (lr) spsr Current Visible Registers Banked out Registers FIQ IRQ SVC Undef Abort r0 r1 r2 r3 r4 r5 r6 r7 r15 (pc) cpsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r8 r9 r10 r11 r12 r13 (sp) r14 (lr) spsr Current Visible Registers Banked out Registers User IRQ SVC Undef Abort r8 r9 r10 r11 r12 r13 (sp) r14 (lr) FIQ Mode IRQ Mode r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r15 (pc) cpsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r8 r9 r10 r11 r12 r13 (sp) r14 (lr) spsr Current Visible Registers Banked out Registers User FIQ SVC Undef Abort r13 (sp) r14 (lr) Undef Mode r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r15 (pc) cpsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r8 r9 r10 r11 r12 r13 (sp) r14 (lr) spsr Current Visible Registers Banked out Registers User FIQ IRQ SVC Abort r13 (sp) r14 (lr) SVC Mode r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r15 (pc) cpsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r8 r9 r10 r11 r12 r13 (sp) r14 (lr) spsr Current Visible Registers Banked out Registers User FIQ IRQ Undef Abort r13 (sp) r14 (lr) Abort Mode r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r15 (pc) cpsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r13 (sp) r14 (lr) spsr r8 r9 r10 r11 r12 r13 (sp) r14 (lr) spsr Current Visible Registers Banked out Registers User FIQ IRQ SVC Undef r13 (sp) r14 (lr) The ARM Register Set
- 10. 10 TM 10 39v10 The ARM Architecture The Registers ARM has 37 registers all of which are 32-bits long. 1 dedicated program counter 1 dedicated current program status register 5 dedicated saved program status registers 30 general purpose registers The current processor mode governs which of several banks is accessible. Each mode can access a particular set of r0-r12 registers a particular r13 (the stack pointer, sp) and r14 (the link register, lr) the program counter, r15 (pc) the current program status register, cpsr Privileged modes (except System) can also access a particular spsr (saved program status register)
- 11. 11 TM 11 39v10 The ARM Architecture Program Status Registers Condition code flags N = Negative result from ALU Z = Zero result from ALU C = ALU operation Carried out V = ALU operation oVerflowed Sticky Overflow flag - Q flag Architecture 5TE/J only Indicates if saturation has occurred J bit Architecture 5TEJ only J = 1: Processor in Jazelle state Interrupt Disable bits. I = 1: Disables the IRQ. F = 1: Disables the FIQ. T Bit Architecture xT only T = 0: Processor in ARM state T = 1: Processor in Thumb state Mode bits Specify the processor mode 27 31 N Z C V Q 28 6 7 I F T mode 16 23 8 15 5 4 0 24 f s x c U n d e f i n e d J
- 12. 12 TM 12 39v10 The ARM Architecture When the processor is executing in ARM state: All instructions are 32 bits wide All instructions must be word aligned Therefore the pc value is stored in bits [31:2] with bits [1:0] undefined (as instruction cannot be halfword or byte aligned). When the processor is executing in Thumb state: All instructions are 16 bits wide All instructions must be halfword aligned Therefore the pc value is stored in bits [31:1] with bit [0] undefined (as instruction cannot be byte aligned). When the processor is executing in Jazelle state: All instructions are 8 bits wide Processor performs a word access to read 4 instructions at once Program Counter (r15)
- 13. 13 TM 13 39v10 The ARM Architecture Vector Table Exception Handling When an exception occurs, the ARM: Copies CPSR into SPSR_<mode> Sets appropriate CPSR bits Change to ARM state Change to exception mode Disable interrupts (if appropriate) Stores the return address in LR_<mode> Sets PC to vector address To return, exception handler needs to: Restore CPSR from SPSR_<mode> Restore PC from LR_<mode> This can only be done in ARM state. Vector table can be at 0xFFFF0000 on ARM720T and on ARM9/10 family devices FIQ IRQ (Reserved) Data Abort Prefetch Abort Software Interrupt Undefined Instruction Reset 0x1C 0x18 0x14 0x10 0x0C 0x08 0x04 0x00
- 14. 14 TM 14 39v10 The ARM Architecture Agenda Introduction to ARM Ltd Programmers Model Instruction Sets System Design Development Tools
- 15. 15 TM 15 39v10 The ARM Architecture ARM instructions can be made to execute conditionally by postfixing them with the appropriate condition code field. This improves code density and performance by reducing the number of forward branch instructions. CMP r3,#0 CMP r3,#0 BEQ skip ADDNE r0,r1,r2 ADD r0,r1,r2 skip By default, data processing instructions do not affect the condition code flags but the flags can be optionally set by using “S”. CMP does not need “S”. loop … SUBS r1,r1,#1 BNE loop if Z flag clear then branch decrement r1 and set flags Conditional Execution and Flags
- 16. 16 TM 16 39v10 The ARM Architecture Examples of conditional execution Use a sequence of several conditional instructions if (a==0) func(1); CMP r0,#0 MOVEQ r0,#1 BLEQ func Set the flags, then use various condition codes if (a==0) x=0; if (a>0) x=1; CMP r0,#0 MOVEQ r1,#0 MOVGT r1,#1 Use conditional compare instructions if (a==4 || a==10) x=0; CMP r0,#4 CMPNE r0,#10 MOVEQ r1,#0
- 17. 17 TM 17 39v10 The ARM Architecture Branch : B{<cond>} label Branch with Link : BL{<cond>} subroutine_label The processor core shifts the offset field left by 2 positions, sign-extends it and adds it to the PC ± 32 Mbyte range How to perform longer branches? 28 31 24 0 Cond 1 0 1 L Offset Condition field Link bit 0 = Branch 1 = Branch with link 23 25 27 Branch instructions
- 18. 18 TM 18 39v10 The ARM Architecture Data processing Instructions Consist of : Arithmetic: ADD ADC SUB SBC RSB RSC Logical: AND ORR EOR BIC Comparisons: CMP CMN TST TEQ Data movement: MOV MVN These instructions only work on registers, NOT memory. Syntax: <Operation>{<cond>}{S} Rd, Rn, Operand2 Comparisons set flags only - they do not specify Rd Data movement does not specify Rn Second operand is sent to the ALU via barrel shifter.
- 19. 19 TM 19 39v10 The ARM Architecture The Barrel Shifter Destination CF 0 Destination CF LSL : Logical Left Shift ASR: Arithmetic Right Shift Multiplication by a power of 2 Division by a power of 2, preserving the sign bit Destination CF ...0 Destination CF LSR : Logical Shift Right ROR: Rotate Right Division by a power of 2 Bit rotate with wrap around from LSB to MSB Destination RRX: Rotate Right Extended Single bit rotate with wrap around from CF to MSB CF
- 20. 20 TM 20 39v10 The ARM Architecture Register, optionally with shift operation Shift value can be either be: 5 bit unsigned integer Specified in bottom byte of another register. Used for multiplication by constant Immediate value 8 bit number, with a range of 0-255. Rotated right through even number of positions Allows increased range of 32-bit constants to be loaded directly into registers Result Operand 1 Barrel Shifter Operand 2 ALU Using the Barrel Shifter: The Second Operand
- 21. 21 TM 21 39v10 The ARM Architecture No ARM instruction can contain a 32 bit immediate constant All ARM instructions are fixed as 32 bits long The data processing instruction format has 12 bits available for operand2 4 bit rotate value (0-15) is multiplied by two to give range 0-30 in steps of 2 Rule to remember is “8-bits shifted by an even number of bit positions”. 0 7 11 8 immed_8 Shifter ROR rot x2 Quick Quiz: 0xe3a004ff MOV r0, #??? Immediate constants (1)
- 22. 22 TM 22 39v10 The ARM Architecture To allow larger constants to be loaded, the assembler offers a pseudo- instruction: LDR rd, =const This will either: Produce a MOV or MVN instruction to generate the value (if possible). or Generate a LDR instruction with a PC-relative address to read the constant from a literal pool (Constant data area embedded in the code). For example LDR r0,=0xFF => MOV r0,#0xFF LDR r0,=0x55555555 => LDR r0,[PC,#Imm12] … … DCD 0x55555555 This is the recommended way of loading constants into a register Loading 32 bit constants
- 23. 23 TM 23 39v10 The ARM Architecture Multiply Syntax: MUL{<cond>}{S} Rd, Rm, Rs Rd = Rm * Rs MLA{<cond>}{S} Rd,Rm,Rs,Rn Rd = (Rm * Rs) + Rn [U|S]MULL{<cond>}{S} RdLo, RdHi, Rm, Rs RdHi,RdLo := Rm*Rs [U|S]MLAL{<cond>}{S} RdLo, RdHi, Rm, Rs RdHi,RdLo := (Rm*Rs)+RdHi,RdLo Cycle time Basic MUL instruction 2-5 cycles on ARM7TDMI 1-3 cycles on StrongARM/XScale 2 cycles on ARM9E/ARM102xE +1 cycle for ARM9TDMI (over ARM7TDMI) +1 cycle for accumulate (not on 9E though result delay is one cycle longer) +1 cycle for “long” Above are “general rules” - refer to the TRM for the core you are using for the exact details
- 24. 24 TM 24 39v10 The ARM Architecture Single register data transfer LDR STR Word LDRB STRB Byte LDRH STRH Halfword LDRSB Signed byte load LDRSH Signed halfword load Memory system must support all access sizes Syntax: LDR{<cond>}{<size>} Rd, <address> STR{<cond>}{<size>} Rd, <address> e.g. LDREQB
- 25. 25 TM 25 39v10 The ARM Architecture Address accessed Address accessed by LDR/STR is specified by a base register plus an offset For word and unsigned byte accesses, offset can be An unsigned 12-bit immediate value (ie 0 - 4095 bytes). LDR r0,[r1,#8] A register, optionally shifted by an immediate value LDR r0,[r1,r2] LDR r0,[r1,r2,LSL#2] This can be either added or subtracted from the base register: LDR r0,[r1,#-8] LDR r0,[r1,-r2] LDR r0,[r1,-r2,LSL#2] For halfword and signed halfword / byte, offset can be: An unsigned 8 bit immediate value (ie 0-255 bytes). A register (unshifted). Choice of pre-indexed or post-indexed addressing
- 26. 26 TM 26 39v10 The ARM Architecture 0x5 0x5 r1 0x200 Base Register 0x200 r0 0x5 Source Register for STR Offset 12 0x20c r1 0x200 Original Base Register 0x200 r0 0x5 Source Register for STR Offset 12 0x20c r1 0x20c Updated Base Register Auto-update form: STR r0,[r1,#12]! Pre or Post Indexed Addressing? Pre-indexed: STR r0,[r1,#12] Post-indexed: STR r0,[r1],#12
- 27. 27 TM 27 39v10 The ARM Architecture Software Interrupt (SWI) Causes an exception trap to the SWI hardware vector The SWI handler can examine the SWI number to decide what operation has been requested. By using the SWI mechanism, an operating system can implement a set of privileged operations which applications running in user mode can request. Syntax: SWI{<cond>} <SWI number> 28 31 24 27 0 Cond 1 1 1 1 SWI number (ignored by processor) 23 Condition Field
- 28. 28 TM 28 39v10 The ARM Architecture PSR Transfer Instructions MRS and MSR allow contents of CPSR / SPSR to be transferred to / from a general purpose register. Syntax: MRS{<cond>} Rd,<psr> ; Rd = <psr> MSR{<cond>} <psr[_fields]>,Rm ; <psr[_fields]> = Rm where <psr> = CPSR or SPSR [_fields] = any combination of ‘fsxc’ Also an immediate form MSR{<cond>} <psr_fields>,#Immediate In User Mode, all bits can be read but only the condition flags (_f) can be written. 27 31 N Z C V Q 28 6 7 I F T mode 16 23 8 15 5 4 0 24 f s x c U n d e f i n e d J
- 29. 29 TM 29 39v10 The ARM Architecture ARM Branches and Subroutines B <label> PC relative. ±32 Mbyte range. BL <subroutine> Stores return address in LR Returning implemented by restoring the PC from LR For non-leaf functions, LR will have to be stacked STMFD sp!,{regs,lr} : BL func2 : LDMFD sp!,{regs,pc} func1 func2 : : BL func1 : : : : : : : MOV pc, lr
- 30. 30 TM 30 39v10 The ARM Architecture Thumb Thumb is a 16-bit instruction set Optimised for code density from C code (~65% of ARM code size) Improved performance from narrow memory Subset of the functionality of the ARM instruction set Core has additional execution state - Thumb Switch between ARM and Thumb using BX instruction 0 15 31 0 ADDS r2,r2,#1 ADD r2,#1 32-bit ARM Instruction 16-bit Thumb Instruction For most instructions generated by compiler: Conditional execution is not used Source and destination registers identical Only Low registers used Constants are of limited size Inline barrel shifter not used
- 31. 31 TM 31 39v10 The ARM Architecture Agenda Introduction Programmers Model Instruction Sets System Design Development Tools
- 32. 32 TM 32 39v10 The ARM Architecture AMBA Bridge Timer On-chip RAM ARM Interrupt Controller Remap/ Pause TIC Arbiter Bus Interface External ROM External RAM Reset System Bus Peripheral Bus AMBA Advanced Microcontroller Bus Architecture ADK Complete AMBA Design Kit ACT AMBA Compliance Testbench PrimeCell ARM’s AMBA compliant peripherals AHB or ASB APB External Bus Interface Decoder
- 33. 33 TM 33 39v10 The ARM Architecture Agenda Introduction Programmers Model Instruction Sets System Design Development Tools
- 34. 34 TM 34 39v10 The ARM Architecture ARM Debug Architecture ARM core ETM TAP controller Trace Port JTAG port Ethernet Debugger (+ optional trace tools) EmbeddedICE Logic Provides breakpoints and processor/system access JTAG interface (ICE) Converts debugger commands to JTAG signals Embedded trace Macrocell (ETM) Compresses real-time instruction and data access trace Contains ICE features (trigger & filter logic) Trace port analyzer (TPA) Captures trace in a deep buffer EmbeddedICE Logic