Freescale Semiconductor SC140 Multi-Register Transfer in Big and Little Endian Modes

Models: SC140

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Memory Interface

This is the desired result. This effect is achieved in little endian mode through logic in the core, which modifies the data on the data bus to the memory for both reads and writes.

Figure 2-23 shows examples of multi-register data transfers in big and little endian modes.

Big Endian

Memory

0 1 2 3 4 5 6 7

00a 0b 0c 0d 0e 0f

801 02 03 04 05 06 07 08

16 ($10) 11 22 33 44 cc dd ee ff

24($18)

32($20)

Little Endian

7

6

5

4

3

2

1

0

0f 0e 0d 0c 0b 0a

07 08 05 06 03 04 01 02

cc dd ee ff 11 22 33 44

0

8

16($10)

24($18)

32($20)

Data Bus Contents

xxxxxxxx 0102 0304

0102 0304 0506 0708

1122 3344 ccdd eeff

XA-BUS

XB-BUS

64-bit

64-bit

Instructions

(a)MOVE.2W (A8), D0:D1

(b)MOVE.4W (A8), D0:D1:D2:D3

(c)MOVE.2L (A16), D0:D1

SC140 Core

Data Bus Contents

xxxxxxxx 0304 0102

0708 0506 0304 0102 ccdd eeff 1122 3344

XA-BUS

XB-BUS

64-bit

64-bit

 

(a)

 

(b)

(c)

 

D0

0102

0102

11223344

 

D1

0304

0304

ccddeeff

 

D2

 

0506

 

D3

 

0708

 

 

 

 

 

 

Figure 2-23.

Multi-Register Transfer in Big and Little Endian Modes

Note: The only exceptions to the behavior described above are the VSL instructions. These instructions cause source data words from the core to be written to different memory locations in big and little endian modes. For more information about the VSL instructions, refer to Table 2-27 on page 2-64, and Appendix A, “Viterbi Shift Left Move (AGU) VSL,” on page A-422..

SC140 DSP Core Reference Manual

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Freescale Semiconductor SC140 specifications Multi-Register Transfer in Big and Little Endian Modes