This discussion has been locked.

You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Question : The Definitive Guide to the ARM Cortex-M3

Note: This was originally posted on 11th December 2007 at http://forums.arm.com

Dear, all.

I am new in this forum.
Recently I studying Cortex-M3 core, so I bought book "The Definitive Guide to the ARM Cortex-M3" by Joseph Yiu.
This book is very good book and this explains most of unaswered questions by TRM or AALRM.

As I found some mistake in this book, I would like to feedback, but I could not find publisher's homepage. Then I found Josephe's name in this forum, I would like to ask here.

In page 42, there is fig 3.11 and 3.12 but this contents is same as fig 3.8 and 3.9.
Fig 3.8 and 3.9 should be some program list.

Can I get correct figure? Or where I should contact?
Please advise.

Kenichi

Parents

0 David Clark over 10 years ago

Note: This was originally posted on 10th April 2010 at http://forums.arm.com

Joseph -

Question about the new IF-THEN construct. Basically, I don't understand the advantage of it over the previous "conditional execution" model that I was so fond of.

It seems that the 2nd edition of the book gives it a little more treatment, which is good, but I'm still not sold on it.

I have 2 problems with it. To illustrate, I'll use the example from the 2nd ed. of the book, table 4.33

OLD ARM CODE WITH CONDITIONAL EXECUTION:
[font="Courier New"]
CMP   R1, #2
ADDEQ R0, R1, #1
[/font]

NEW CODE WITH IF-THEN:
[font="Courier New"]CMP   R1, #2
IT    EQ
ADDEQ R0, R1, #1[/font]

Forgive me for being cynical, but what I see is:

(1) More code (3 instructions vs. 2). This is not good for 2 reasons:
   - longer execution time (* maybe it's not, I'm not up to speed)
   - more code to maintain (3 source lines vs. 2)

(2) Potential for inconsistency. Isn't the EQ suffix on the ADD redundant? The way I read "IT EQ" is "If EQ evaluates to TRUE, THEN execute the next 1 instruction, otherwise don't." So WHY do we need the EQ suffix on ADD?!?!? Put another way, what would happen with the following code, would the assembler just spit out an error?

[font="Courier New"]CMP R1, #2
IT EQ
ADDNE R0, R1, #1[/font]

So in other words, the conditional suffix doesn't match up with the ITEQ. This situation cannot happen with the old syntax.

I will admit I haven't spent lots of time understanding the construct, but IF-THEN seems like a step backwards in code maintainability, and at best a wash when it comes to performance. Actually it seems like the performance would be worse. The engineers I've worked with ARM are smart, so clearly I'm missing something (I'm being serious). Sorry if these issues are addressed in the book, I don't have it handy & I wanted to send this off before I forget.

Please help sell me on the IF-THEN construct!

Thanks.
Cancel
Up 0 Down

Cancel

Reply

0 David Clark over 10 years ago

Note: This was originally posted on 10th April 2010 at http://forums.arm.com

Joseph -

Question about the new IF-THEN construct. Basically, I don't understand the advantage of it over the previous "conditional execution" model that I was so fond of.

It seems that the 2nd edition of the book gives it a little more treatment, which is good, but I'm still not sold on it.

I have 2 problems with it. To illustrate, I'll use the example from the 2nd ed. of the book, table 4.33

OLD ARM CODE WITH CONDITIONAL EXECUTION:
[font="Courier New"]
CMP   R1, #2
ADDEQ R0, R1, #1
[/font]

NEW CODE WITH IF-THEN:
[font="Courier New"]CMP   R1, #2
IT    EQ
ADDEQ R0, R1, #1[/font]

Forgive me for being cynical, but what I see is:

(1) More code (3 instructions vs. 2). This is not good for 2 reasons:
   - longer execution time (* maybe it's not, I'm not up to speed)
   - more code to maintain (3 source lines vs. 2)

(2) Potential for inconsistency. Isn't the EQ suffix on the ADD redundant? The way I read "IT EQ" is "If EQ evaluates to TRUE, THEN execute the next 1 instruction, otherwise don't." So WHY do we need the EQ suffix on ADD?!?!? Put another way, what would happen with the following code, would the assembler just spit out an error?

[font="Courier New"]CMP R1, #2
IT EQ
ADDNE R0, R1, #1[/font]

So in other words, the conditional suffix doesn't match up with the ITEQ. This situation cannot happen with the old syntax.

I will admit I haven't spent lots of time understanding the construct, but IF-THEN seems like a step backwards in code maintainability, and at best a wash when it comes to performance. Actually it seems like the performance would be worse. The engineers I've worked with ARM are smart, so clearly I'm missing something (I'm being serious). Sorry if these issues are addressed in the book, I don't have it handy & I wanted to send this off before I forget.

Please help sell me on the IF-THEN construct!

Thanks.
Cancel
Up 0 Down

Cancel

Children

No data