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Intel ARM Cortex-A9, Руководство по введению

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I

NTRODUCTION TO THE

ARM

®

P

ROCESSOR

U

SING

I

NTEL

FPGA T

OOLCHAIN

For Quartus Prime 16.1

The suffix AL (Always) causes the unconditional branch. The same effect is achieved if there is no suffix appended.
The Assembler interprets the instruction

B LABEL

as being the same as

BAL LABEL

6.12

Subroutine Linkage Instructions

Subroutine calls are achieved with the

Branch and Link

instruction

BL

Destination

where the

Destination

is typically the label of the first instruction in the subroutine. In addition to behaving as a

Branch instruction, this instruction saves the return address (which is the address of the instruction that follows the
BL instruction) in the Link register, R14.

There is no specific

return-from-subroutine

instruction. The return from a subroutine can be performed by an in-

struction that loads the contents of R14 into R15, such as

MOV PC, LR

Since LR can hold only one return address, it follows that if nested subroutines are used it is necessary to save the
contents of R14, typically on the stack, prior to a nested subroutine call.

We should also mention that in the ARM environment, there is a convention that registers R0 to R4 are used to pass
parameters to a subroutine, while register R0 is used to return a result. If more than four parameters are needed, then
some of the parameters have to be passed via the stack.

7

Assembler Directives

Assembler directives provide information used by the assembler when assembling an application program. Different
assemblers often use different assembler directives. We will restrict our discussion to the assembler that is used by
the Intel FPGA Monitor Program. This assembler conforms to the widely used GNU Assembler, which is software
available in the public domain. Thus, the GNU Assembler directives can be used in ARM programs intended to be
used with the Intel FPGA Monitor Program.

Assembler directives begin with a period. We describe some of the more frequently used assembler directives below.

Intel Corporation - FPGA University Program

November 2016

17

Содержание ARM Cortex-A9

Страница 1: ...an ARM based system on Intel s DE1 SOC board A full description of ARM processors is provided in the ARM Architecture Reference Manual which is available on the ARM Holdings web site Contents Overvie...

Страница 2: ...ral purpose registers R0 to R14 a Program Counter R15 and a Current Program Status Register CPSR as shown in Figure 1 All general purpose registers can be used in the same way However software program...

Страница 3: ...s called banked registers for saving the contents of primary registers when various types of interrupts occur as discussed in Section 10 4 Instruction Sets The ARM Cortex A9 processor can execute inst...

Страница 4: ...base register and a value that is either given as a signed 12 bit offset directly in the instruction or as a magnitude in the index register The magnitude in Rm can be scaled by shifting it either lef...

Страница 5: ...hift Address Rn Rn Rn Rm shifted offset a signed number given in the instruction shift direction integer where direction is LSL for left shift or LSR for right shift and integer is a 5 bit unsigned nu...

Страница 6: ...will determine the immediate offset as the difference between the address MEMLOC and the contents of the updated Program Counter It will generate the instruction LDR R2 R15 offset This offset takes in...

Страница 7: ...emory and I 0 interfaces and the general purpose registers The LDR Load Register instruction illustrated in the previous section loads a 32 bit operand into a register The corresponding Store instruct...

Страница 8: ...o not have to be contiguous A range of registers is specified by listing the first and the last registers in the range separated by a dash In the resulting machine instruction each register is identif...

Страница 9: ...B SP R1 R3 R5 The instruction POP R1 R3 R5 restores the contents of these registers from the stack The equivalent Load Multiple instruction would be LDMIA SP R1 R3 R5 6 2 Data Processing Instructions...

Страница 10: ...its value can be shifted before being used If it is shifted then the shifting amount can be specified as a five bit constant as in OP Rd Rn Rm LSL 3 or as the least significant byte of a register Rs...

Страница 11: ...in ADD R0 R1 24 The Assembler will implement this operation with the Subtract instruction SUB R0 R1 24 6 4 1 Multiplication There are two versions of multiplication instructions MUL Multiply MLA Mult...

Страница 12: ...uctions that perform logic operations for testing purposes The Test instruction TST Rn Operand2 performs the AND operation using the contents of Rn and Operand2 and sets the condition code flags based...

Страница 13: ...sing mode to access the literal pool The Assembler decides where in memory to place the literal pool typically it is immediately following the program s machine code A constant may be represented by a...

Страница 14: ...wo registers or the contents of a register and an immediate value and set the condition code flags based on the result The Compare instruction CMP Rn Operand2 performs the comparison by subtracting th...

Страница 15: ...f data processing instructions is OP S cond Rd Rn Operand2 The conditions that can be specified are those in Table 2 Observe that there are 14 patterns for conditions that depend on the condition code...

Страница 16: ...d operation of the ARM processor The branch instruction is executed conditionally based on the current setting of the Condition Code flags The conditions that can be specified are given in Table 2 For...

Страница 17: ...that if nested subroutines are used it is necessary to save the contents of R14 typically on the stack prior to a nested subroutine call We should also mention that in the ARM environment there is a c...

Страница 18: ...ymbol visible outside the assembled object file hword expressions Expressions separated by commas are specified Each expression is assembled into a 16 bit number include filename Provides a mechanism...

Страница 19: ...st instruction in the program The execution of the program ends by continuously looping on this instruction text global _start _start LDR R0 AVECTOR Register R0 is a pointer to vector A LDR R1 BVECTOR...

Страница 20: ...d by a program executing a Supervisor Call instruction SVC It is also entered on reset or power up Abort mode is entered if a program attempts to access a non existing memory location Undefined mode i...

Страница 21: ...re efficient some other registers are involved These registers are shown in blue in Figure 4 They are called the banked registers There is a different set of banked registers for each exception mode A...

Страница 22: ...service routine needs to use some of these registers the contents of the registers must be saved on the stack and later restored However having the five banked registers R8_fiq to R12_fiq in the FIQ m...

Страница 23: ...anked saved status register that is accessed Thus MRS Rd SPSR copies the contents of SPSR_irq into register Rd 11 Exception Processing An exception in the normal flow of program execution can be cause...

Страница 24: ...A software interrupt which is called a software exception in ARM literature occurs when an SVC instruction is encountered in a program This instruction causes the processor to switch into Supervisor m...

Страница 25: ...e processor saves the contents of CPSR in the SPSR_irq register and it saves the contents of PC in the link register LR_irq It also sets the mode bits in CPSR to denote the IRQ exception mode and it s...

Страница 26: ...d with the instruction SUBS PC LR 8 11 6 Nested Interrupts When two or more interrupts or exceptions occur at different priority levels causing the processor to enter different modes of operation thei...

Страница 27: ...gure 5 illustrates the structure of the code that can be used text global _start LDR PC _start Go to the beginning of the MAIN program LDR PC SERVICE_UND Unimplemented instruction LDR PC SERVICE_SVC S...

Страница 28: ...al to ensure that the cached data is not used instead of the current values in the I O device registers In effect the data cache has to be bypassed when reading or writing the registers in I O devices...

Страница 29: ...ifications in accordance with Intel s stan dard warranty but reserves the right to make changes to any products and services at any time without notice Intel assumes no responsibility or liability ari...

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