Level Two Interface

Table 9-18shows possible values of AWADDRM, AWBURSTM, AWSIZEM, and AWLENM for an STR or an STM that transfers one register, an STM1, to Normal memory through the AXI master port.

Table 9-18 STR or STM1 to Cacheable write-through or Non-cacheable Normal memory

Address[2:0]

AWADDRM

AWBURSTM

AWSIZEM

AWLENM

WSTRBM

 

 

 

 

 

 

 

0x0

(byte 0) (word 0)

0x00

Incr

32-bit

1 data transfer

b00001111

 

 

 

 

 

 

 

0x1

(byte 1)

0x01

Incr

64-bit

1 data transfer

b00011110

 

 

 

 

 

 

 

0x2

(byte 2)

0x00

Incr

64-bit

1 data transfer

b00111100

 

 

 

 

 

 

 

0x3

(byte 3)

0x03

Incr

64-bit

2 data transfers

b01111000

 

 

 

 

 

 

b00000000

 

 

 

 

 

 

 

0x4

(byte 4) (word 1)

0x04

Incr

32-bit

1 data transfer

b11110000

 

 

 

 

 

 

 

0x5

(byte 5)

0x05

Incr

32-bit

2 data transfers

b11100000

 

 

 

 

 

 

b00000001

 

 

 

 

 

 

 

0x6

(byte 6)

0x06

Incr

16-bit

1 data transfer

b11000000

 

 

0x08

Incr

16-bit

1 data transfer

b00000011

 

 

 

 

 

 

 

0x7

(byte 7)

0x04

Incr

32-bit

2 data transfers

b10000000

 

 

 

 

 

 

b00000111

 

 

 

 

 

 

 

9.3.7AXI transaction splitting

The processor splits AXI bursts when it accesses addresses across a cache line boundary, that is, a 32-byte boundary. An instruction which accesses memory across one or two 32-byte boundaries generates two or three AXI bursts respectively. The following examples show this behavior. They are provided as examples only, and are not an exhaustive description of the AXI transactions. Depending on the state of the processor, and the timing of the accesses, the actual bursts generated might have a different size and length to the examples shown, even for the same instruction.

For example, LDMIA R10, {R0-R5}loads six words from memory. The number of AXI transactions generated by this instruction depends on the base address, R10:

If all six words are in the same cache line, there is a single AXI transaction. For example, for LDMIA R10, {R0-R5}with R10 = 0x1008, the interface might generate a burst of three, 64-bit read transfers, as shown in Table 9-19.

Table 9-19 AXI transaction splitting, all six words in same cache line

ARADDRM ARBURSTM ARSIZEM ARLENM

0x1008

Incr

64-bit

3 data transfers

 

 

 

 

ARM DDI 0363E

Copyright © 2009 ARM Limited. All rights reserved.

9-16

ID013010

Non-Confidential, Unrestricted Access

 

Page 249
Image 249
ARM R4F, r1p3 manual AXI transaction splitting