Background Debug Mode (BDM)

29.5.3.1 ColdFire BDM Command Format

All ColdFire Family BDM commands include a 16-bit operation word followed by an optional set of one or more extension words, as shown in Figure 29-15.

15

10

9

8

7

6

5

4

3

2

0

Operation

0

R/W

Op Size

0

0

A/D

Register

Extension Word(s)

Figure 29-15. BDM Command Format

Table 29-18describes BDM fields.

 

 

 

Table 29-18. BDM Field Descriptions

 

 

 

 

 

Bit

Name

 

 

Description

 

 

 

15–10

Operation

Specifies the command. These values are listed in Table 29-17.

 

 

 

9

0

Reserved, should be cleared.

 

 

 

8

R/W

Direction of operand transfer.

 

 

0 Data is written to the CPU or to memory from the development system.

 

 

1 The transfer is from the CPU to the development system.

 

 

 

7–6

Op Size

Operand data size for sized operations. Addresses are expressed as 32-bit absolute values. Note that a

 

 

command performing a byte-sized memory read leaves the upper 8 bits of the response data undefined.

 

 

Referenced data is returned in the lower 8 bits of the response.

 

 

 

Operand Size

Bit Values

 

 

00

Byte

8 bits

 

 

01

Word

16 bits

 

 

10

Longword

32 bits

 

 

11

Reserved

 

 

 

5–4

00

Reserved, should be cleared.

 

 

 

3

A/D

Address/data. Determines whether the register field specifies a data or address register.

 

 

0 Indicates a data register.

 

 

1 Indicates an address register.

 

 

 

2–0

Register

Contains the register number in commands that operate on processor registers.

 

 

 

 

 

29.5.3.1.1 Extension Words as Required

Some commands require extension words for addresses and/or immediate data. Addresses require two extension words because only absolute long addressing is permitted. Longword accesses are forcibly longword-aligned and word accesses are forcibly word-aligned. Immediate data can be 1 or 2 words long. Byte and word data each requires a single extension word and longword data requires two extension words.

Operands and addresses are transferred most-significant word first. In the following descriptions of the BDM command set, the optional set of extension words is defined as address, data, or operand data.

MOTOROLA

Chapter 29. Debug Support

29-21

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Motorola MCF5281 ColdFire BDM Command Format, 18describes BDM fields, Extension Words as Required, BDM Field Descriptions