68k ASM寻址模式

Question

我在大学学习了68k / Coldfire，并且难以理解更复杂的寻址模式（数字位于取消引用的括号附近）。

我认为最好的例子是：

A) lea:
A1) lea $5(a1,a2.l), a0
A2) lea -1(a1,a2), a0

B) move:
B1) move.b 1(a1),d0
B2) move.b -2(a1),d0

谁能用简单的语言解释我，每条指令中发生了什么？

如果需要，请详细说明（增加/增加前后等）。

谢谢！！;）

Answer 1

广告说明：

• A1）A0将设置为A1 + A2 + 5
• A2）A0将下注设置为A1 + A2-1

As the name of the lea instructions implies, it is used to load an address into an address register. It will not move data from indirect addressing. I haven't checked if those instructions are valid and my 68k skills are quite rusty now, so I assume they are. Not specifying the index register width in A2 introduces ambiguity. From the top of my head I cannot recollect if .W or .L was the default register width here, so specifying that might be a good idea.

Ad move instructions:

• B1) D0 will be set to the byte that immediately follows the address stored in A1. E.g. if A1 is set to $1000, the byte that will be read is the one at address $1001.
• B2) As in B1, but the content will be readm from 2-bytes ahead the A1 address. Again assuming A1 will be preloaded with $1000, the byte that will be read is the one at location $FFE.

For completeness, the addressing modes are:

• A1) Register indirect with index and displacement
• A2) dito
• B1) Register indirect with displacement
• B2) dito