Chapter 11. Debug Support
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11-33
Background Debug Mode (BDM)
11.5.3.1 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 11-20.
Table 11-25 describes BDM fields.
11.5.3.1.1 Extension Words as Required
Some commands require extension words for addresses 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.
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 11-20. BDM Command Format
Table 11-25. BDM Field Descriptions
Bit
Name
Description
15–10
Operation Specifies the command. These values are listed in Table 11-24.
9
0
Reserved
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
Operand
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
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.
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