Dsp Add Rs Modes

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Data addressing modes providevarious ways to access operands to

execute instructions and placeresults in the memory or theregisters.


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In immediate addressing, the instruction syntaxcontains the specific value of the operand.

Two types of values can be encoded in aninstruction:

Short immediate values can be 3, 5, 8, or 9 bits inlength.

Long immediate values are always 16 bits inlength.

Immediate values can be encoded in 1-word or 2-word instructions. The 3-, 5-, 8-, or 9-bit values are encoded into 1-

word instructions; 16-bit values are encoded into 2-word instructions.


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The length of the immediate value encoded in aninstruction depends on the type of instruction used.


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The syntax for immediate addressing uses anumber sign (#) immediately preceding the

value or symbol to indicate that it is animmediate value.

For example, to load accumulator A with thevalue 80 in hexadecimal, LD #80h, A

RPT instruction: a long-immediate (#lk) valueis encoded in instructions that use immediateaddressing.

The opcode of the instruction is encoded in the

high half of the instruction, bits 015 of thehigh word of a 2-word encoding.

The value of the constant is in the remaininginstruction space.


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Data-memory address (dmad) addressing: MVDK Smem, dmad, MVDM dmad, MMR, MVKD dmad,

Smem MVMD MMR, dmad Program-memory address (pmad) addressing:

FIRS Xmem, Ymem, pmad MACD Smem, pmad, src MACP Smem, pmad, src MVDP Smem, pmad MVPD

pmad, Smem Port address (PA) addressing: PORTR PA, Smem PORTW Smem, PA

*(lk) addressing is used with all instructions that support theuse of a single data-memory (Smem) operand. Absolute addresses are always encoded with a length of 16

bits, so instructions that encode absolute addresses arealways at least two words in length.


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dmad Addressing

Data-memory address (dmad) addressing uses aspecific value to specify an address in data space.

The syntax for dmad addressing uses a symbol ora number to specify an address in data space.

For example, to copy the value contained at theaddress labeled SAMPLE in data space to thememory location in data space pointed to by AR5,one would write:

MVKD SAMPLE, *AR5 In this example, the address referenced by

SAMPLE is the dmad value.


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pmad Addressing

Program-memory address (pmad) addressing usesa specific value to specify an address in programspace.

The syntax for pmad addressing uses a symbol or a

number to specify an address in program space. For example, to copy a word in the program

memory location labeled TABLE to a data-memorylocation specified by AR7, one would write:

MVPD TABLE, *AR7 In this example, the address referenced by TABLE

is the pmad value.


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PA Addressing

Port address (PA) addressing uses a specificvalue to specify an external I/O port address.

The syntax for PA addressing uses a symbol ora number to specify the port address.

For example, to copy a value from the I/O portat port address FIFO to a data-memory locationpointed to by AR5, one would write:

PORTR FIFO, *AR5

In the example, FIFO refers to the port address.


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*(lk) Addressing

*(lk) addressing uses a specific value to specify anaddress in data space.

The syntax for *(lk) addressing uses a symbol or anumber to specify an address in data space.

For example, to load accumulator A with the valuecontained in address BUFFER in data space, onewould write:

LD *(BUFFER),A

The syntax for *(lk) addressing allows allinstructions that use Smem addressing to accessany location in data space without changing theDP or initializing an AR.


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Accumulator Addressing: Accumulator addressing uses the value in the

accumulator as an address. This addressing mode is used to address program

memory as data. Two instructions allow to use the accumulator as

an address: READA Smem, WRITA Smem READA transfers a word from a program-memory

location specified by accumulator A to a data-memory location specified by the single data-

memory (Smem) operand of the instruction. WRITA transfers a word from a data-memorylocation specified by the Smem operand of theinstruction to a program-memory locationspecified by accumulator A.


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Direct Addressing

In direct addressing, the instruction containsthe lower seven bits of the data memory

address (dma).

The 7-bit dma is an address offset that is

combined with a base address, with the data-page pointer (DP), or with the stack pointer(SP) to form a 16-bit data-memory address.

Using this form of addressing, you can access

any of 128 locations in random order withoutchanging the DP or the SP.


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Either DP or SP can be combined with the dma offset to generate theactual

address. The compiler mode bit (CPL), located in status register ST1,selects

which method is used to generate the address: When CPL = 0, the dma field is concatenated with the 9-bit DP field to

form the 16-bit data-memory address. When CPL = 1, the dma field is added (positive offset) to SP to form

the

16-bit data-memory address. The syntax for direct addressing uses a symbol or a number to specify the

offset value. For example, to add the contents of the memory location SAMPLE to accumulator B, provided that the correct base address is in DP (CPL =

0) or SP (CPL = 1), you would write: ADD SAMPLE, B The lower seven bits of the address of SAMPLE are stored in the

instruction word.


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In DP-referenced direct addressing, the 7-bit dma inthe instruction register is concatenated with the 9-bit

DP to form the address. DP-referenced direct addressing divides memoryinto 512 pages, because the DPs range is from 0 to511 (29 1). Each page has 128 addressable locations,because the dma ranges from 0 to 127 (27 1).

In other words, the DP points to one of 512 possible128-word data-memory pages; the dma points to thespecific location within that page.

The only difference between an access to location 0on page 1 and to location 0 on page 2 is the value ofthe DP.

The DP is loaded by the LD instruction.


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SP-ReferencedDirect Addressing

In SP-referenced direct addressing, the 7-bitdma in the instruction register is added as apositive offset to the SP to form the effective 16-bit data-memory address.

The SP points to any address in memory. Thedma points to the specific location on the page,allowing you to access a contiguous 128-word(2^7 1) block in memory from any base

address. SP can also add or remove items from the

stack.


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Indirect Addressing:

In indirect addressing, any location in the 64K-word data space can be accessed using the 16-bit address contained in an auxiliary register.

The C54xDSP has eight 16-bit auxiliary

registers (AR0AR7). Indirect addressing is used mainly when there

is a need to step through sequential locations inmemory in fixed-size steps.


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When memory is addressed with indirectaddressing, the auxiliary register and the

address can be optionally modified by adecrement, an increment, an offset, or an index.

Special modes offer circular and bit-reversedaddressing. A circular buffer size register (BK)

is used with circular addressing. The AR0 register is used for indexed and bit-

reversed addressing modes in addition tobeing used to point to memory as the otherauxiliary registers do.


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Indirect addressing is flexible enough not onlyto read or write a single 16-bit data operandfrom memory with one instruction, but also toaccess two data memory locations with oneinstruction.

Accesses of two data-memory locations includereads of two independent memory locations,reads and writes of two consecutive memorylocations, and a read of one memory

location combined with a write to a memorylocation.


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ARAU and Address-Generation Operation

Two auxiliary register arithmetic units(ARAU0 and ARAU1) operate on the contentsof the auxiliary registers.

The ARAUs perform unsigned, 16-bit auxiliary

register arithmetic operations.

Some addresses can be obtained bypremodifying the auxiliary register.


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Memory-mapped register addressing is used tomodify the memory-mapped registers withoutaffecting either the current data-page pointer(DP) value or the current stack-pointer (SP)

value. Because DP and SP do not need to be modified

in this mode, the overhead for writing to aregister is minimal.

Memory-mapped register addressing works forboth direct and indirect addressing.


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Addresses are generated by:

Forcing the nine most significant bits (MSBs) ofdata-memory address to 0, regardless of thecurrent value of DP or SP when directaddressing is used

Using the seven LSBs of the current auxiliaryregister value when indirect addressing is used

If AR1 is used to point to a memory-mappedregister in memory mapped registeraddressing mode and it contains a value ofFF25h.


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Then AR1 points to the timer period register

(PRD), since the seven LSBs of AR1 are 25h

and the address of the PRD is 0025h. After execution, the value remaining in AR1 is

0025h.


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The system stack is used to automatically storethe program counter during interrupts andsubroutines.

The stack is filled from the highest to the

lowest memory address. The processor uses a16-bit memory mapped register, the stackpointer (SP), to address the stack.

SP always points to the last element stored

onto the stack.


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Four instructions access the stack using thestack addressing mode:

PSHD pushes a data-memory value onto thestack.

PSHM pushes a memory-mapped register onto

the stack. POPD pops a data-memory value from the

stack.

POPM pops a memory-mapped register fromthe stack.


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A push predecrements and a pop postincrements

the address in the SP.


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Other operations also affect the stack and the

stack pointer. The stack is used during interrupts and

subroutines to save and restore the PCcontents.

When a subroutine is called or an interruptoccurs, the return address is automaticallysaved in the stack using a push operation.

When a subroutine returns, the return addressis retrieved from the stack using a popoperation and loaded into the PC.


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Circular Addressing:

Many algorithms, such as convolution,correlation, and FIR filters, require theimplementation of a circular buffer in memory.

In these algorithms, a circular buffer is a sliding

window containing the most recent data. Asnew data comes in, the buffer overwrites theoldest data.

The key to the implementation of a circular

buffer is the implementation of circularaddressing.


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The circular-buffer size register (BK) specifiesthe size of the circular buffer.

A circular buffer of size R must start on a N-bitboundary (that is, the N LSBs of the baseaddress of the circular buffer must be 0), whereN is the smallest integer that satisfies 2N> R.

The value R must be loaded into BK. For eg, a31-word circular buffer must start at an addresswhose five LSBs are 0 (that is, XXXX XXXXXXX0 00002), and the value 31 must be loadedinto BK.


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A 32-word circular buffer must start at anaddress whose six LSBs are 0 (that is, XXXX

XXXX XX00 00002), and the value 32 must beloaded into BK.

The effective base address (EFB) of the circularbuffer is determined by zeroing the N LSBs of auser-selected auxiliary register (ARx).

The end of buffer address (EOB) of the circularbuffer is determined by replacing the N LSBs of

ARx with the N LSBs of BK.


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The index of the circular buffer is simply the NLSBs of ARx and the step is the quantity being

added to or subtracted from the auxiliaryregister.

RULES: Place the first (lowest) address of thecircular buffer on a 2N boundary where 2N is

larger than the circular buffer size. Use a step less than or equal to the circular

buffer size.

The first time the circular queue is addressed,the auxiliary register must point to an elementin the circular queue.


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The algorithm for circular addressing is asfollows: If 0


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Bit-reversed addressing enhances executionspeed and program memory for FFTalgorithms that use a variety of radixes. In thisaddressing mode, AR0 specifies one half of the

size of the FFT. The value contained in AR0 must be equal to

2N1, where N is an integer, and the FFT size is2N.

An auxiliary register points to the physicallocation of a data value.


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When you add AR0 to the auxiliary registerusing bit-reversed addressing, the address isgenerated in a bit-reversed fashion, with thecarry bit propagating from left to right, insteadof the normal right to left.


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Dual data-memory operand addressing is usedfor instructions that perform two reads or asingle read and a parallel store (indicated by

two vertical bars, ||) at the same time. Theseinstructions are all one word long and operatein indirect addressing mode only.

Two data-memory operands are represented

by Xmem and Ymem: Xmem is a read operand with access through

the D bus.


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Ymem is used as a read operand in instructions

with dual reads (accessed through the C bus)or as a write operand in instructions with aparallel store (accessed through the E bus).

Because only two bits are available for

selecting each auxiliary register in this mode,only four of the auxiliary registers can be used,AR2 AR5.


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Dsp Add Rs Modes