Hello. I copied "LCD_4bit.c" and "LCD.h" files from Keil examples folder to my project folder and add it to my project. Then I changed Pins definition in "LCD_4bit.c" according to my project board LCD pins(LPC 2378). (I don't think that The problem is here.) Then I could successfully Build it, but when I download it to my project board,there is no signs that LCD works. However when I compile "LCD_4bit.c" in IAR environment ,the produced "hex file" works well on my project board. Thanks for your help.
So, clearly, there must be something non-portable about this software, and/or some critical differences about the way you have your projects configured.
A prime suspect would be Timing - in particular, any HLL delay loops:
www.8052.com/.../162556
You need to start debugging to find where, exactly, the problems are:
www.8052.com/.../120313
" you can never predict the duration of any piece of high-level language (HLL) source code[1]. "
I will expand it for you:
1) you cannot predict the duration of many (assembler) instructions; 2) you can never predict the duration of any series of (assembler) instructions.
does that mean you should stop using assembler to code delays?
"not at the time of writing the (HLL) code but certainly after the compilation"
But that was my point: you cannot predict it - you can only examine it after the fact.
With a HLL, you have no chance of predicting the delay;
In Assembler, you can see the actual instruction sequence, so you can know to what extent its execution time is predictable, and make your prediction within known limits.
"in most applications, we don't need (absolutely) precise delays"
True, but the duration of a HLL loop could vary by orders of magnitude depending on how, exactly, the compiler decides to implement it.
"the bigger your tolerance for in-precision"
I think the tolerance may be quite low for timing an LCD interface...
but you are supposed to have understood it.
Actually I understood your sweepingly generalized statement so well that it took me less than a minute to come up with a counter-example. Which worked so well you didn't even have the guts to quote it in your reply, turning it into one of those 100% pure ad-hominems we've become used to from you.
You appear to be under the impression that anything you say must be correct simply becuase you said so. You couldn't be any more wrong if you tried hard.
you have that with HLLs too:
No.
if not at the time of writing the (HLL) code but certainly after the compilation and having looked at the disassembly.
.. but that only holds until the next time you run the compiler and/or linker, with modifications somewhere else in the source code, or a different compiler version, or just different switch settings.
Looking at what the compiler did today doesn't, in general, tell you anything about what will happen tomorrow. If you want a specific machine code sequence to look the same everytime, you have to write it in assembly.
To summarize: writing delays in pure software (without reference to a hardware time of some sorts) is already a bad idea --- writing them in any other language above assembly, however, is lunacy.
"With a HLL, you have no chance of predicting the delay;"
you certainly have a chance of predicting a HLL delay. I do it all the time.
"In Assembler, you can see the actual instruction sequence, so you can know to what extent its execution time is predictable, and make your prediction within known limits."
only after you have examined the code in its totality.
for a "dumb-ass" example, the following code:
NOP; NOP;
has an undetermined and undeterminable duration without knowing what's happening outside of that sequence, even if each NOP has a finite and well defined execution duration.
so in both cases, you have to examine the generated code to figure out how long the execution will take place, and in some cases even looking at the assembly you wouldn't be able to tell its execution duration.
"True, but the duration of a HLL loop could vary by orders of magnitude depending on how, exactly, the compiler decides to implement it."
the same holds true for assembly too.
"I think the tolerance may be quite low for timing an LCD interface..."
it depends on the actual display. for example, many hd44780 controllers can tolerate initial delay as short as 0.5ms (specification is 15ms), and the longest I have tried is 10s.
"it took me less than a minute to come up with a counter-example."
that's why no one gives a rat's real @#$ to being able to come up with a wrong answer quickly.
try harder next time.
"has an undetermined and undeterminable duration"
How so?
<QUOTE>"How so?"</QUOTE>
the sequence can be in interrupted
always yo're freind.
Zeusti
Yes, of course - for any timing loop you would have to disable interrupts.
That was already covered in the linked thread: www.8052.com/.../149030
(under "Addendum")
"If you want a specific machine code sequence to look the same everytime..."
Which, of course, is fundamental to having a predictable time delay
"...you have to write it in assembly"
Yes, that is the point.
And, if it can't be done in assembly, then it can't be done at all.
Things like caches, pipelines, etc can certainly complicate the issue...
My Keil installation has 46 files named "LCD_4bit.c"
16 have a filesize of 12K; 10 have a filesize of 13K; 20 have a filesize of 14K.
At a quick check, it appears that the 12K files are all the same, the 13K files are all the same, and the 14K files are all the same.
Sampling one of each set shows that they do all contain 'C' for loop delays.
Therefore you cannot just drop these files into any arbitrary project and assume that they will work - you must check that the delays work appropriately with your particular project.
(A check would also be necessary for assembler delays, but it wouldn't have to include checking the code generation).
At a quick check, the code does not disable interrupts during these delays.
<QUOTE>At a quick check, the code does not disable interrupts during these delays.</QUOTE>
most text LCD timing needs minimum delay not precise. disabling interrupts not usually needed.
"...disabling interrupts not usually needed"
Probably true.
However, the minimum delay that a HLL loop might produce is zero - if the loop gets optimised away.
BTW: You do realise that this forum does not support <QUOTE>...</QUOTE> tags - don't you?
<QUOTE>However, the minimum delay that a HLL loop might produce is zero - if the loop gets optimised away.</QUOTE>
yes i know
<QUOTE>BTW: You do realise that this forum does not support <QUOTE>...</QUOTE> tags - don't you?</QUOTE>
Always yo're freind.
Zeusti.
"yes i know"
But you said that it's the minimum delay that's important here!
<QUOTE>But you said that it's the minimum delay that's important here!</QUOTE>
i was answering about what you said about interrupts
do you know that if hll optimizes delay away then protecting the optimized delay from interrupts isnt going to do much? why highlight that?
obviously if hll delay is not optimized away you have minimum delay and you do not need interrupt protection.
Why would you need interrupt protection in the first place? Interrupts during the delay will surely extend the duration of the loop IF it does not use a hardware timer as reference (and maybe even if it does).
The point is, Zooeesti, that you mix up largely unrelated stuff.
I just made two observations about those source files:
1. That they do use HLL loops for delays;
2. That they do not seem to disable interrutps during those loops.
<QUOTE>Why would you need interrupt protection in the first place? Interrupts during the delay will surely extend the duration of the loop</QUOTE>
Tapeer,
you get it, late again and probebly taking all credit for the wisdom.
look for the word <BOLD>minimum</BOLD> in your fav reference book
But, again, you have no idea what code will be generated - the compiler might generate a very "tight" loop, or a rather slow one.
So you have no idea what this minimum delay will be.
Therefore, you have no idea if it will meet the requirements of the application (the requirement of the LCD, in this case).
Therefore, you have no idea if the code will work.
Given that the OP has code that does not work, this would certainly be one ofthe first things to check...
oh it looked like you were connecting them.
<SOB>and we call ourselves engineers</SOB>
"How so?"
Andy, that's very disappointing, to say the least.
"Yes, of course - for any timing loop you would have to disable interrupts."
so that particular sequence's execution is contingent on something outside of it. aka. the execution of that particular sequence itself is indeterminant.
btw, that's the same criticism you put on HLL delays.
not to mention other reasons that particular sequence may give indeterminant execution duration.
"(under "Addendum")"
so if the advocate of HLL delays had an addendum stating that you have to examine its disassembler output, you would have been OK with the use of HLL delays?
many of your criticism for HLL delays is valid. it is just that the same criticism can be leveled against pretty much any software solutions, including assembler code.
to use any solution successfully, you have to understand their limitations. and software delays (assembler or HLL) have plenty of limitations. As a programmer, you just need to understand what they are and use them when they are more / most efficient.
"Therefore you cannot just drop these files into any arbitrary project and assume that they will work - you must check that the delays work appropriately with your particular project."
that (dropping in those files and assuming that they will work) isn't something you can do to any code, assembler or otherwise.
if your yardstick is to drop and pray, you should not use any software based delays.
"I just made two observations about those source files:"
congratulations on passing the 1st trimester of Programming 101.
As far as I understand, the only (?) thing that can undermine the execution duration prediction of these instructions is the pipeline and pipeline-related effects.
And of course - interrupts, as mentioned earlier.
"But, again, you have no idea what code will be generated - the compiler might generate a very "tight" loop, or a rather slow one."
the same is true for any HLL code. does that mean you should stop coding in C?
"So you have no idea what this minimum delay will be."
you do.
"Therefore, you have no idea if it will meet the requirements of the application (the requirement of the LCD, in this case)."
"Therefore, you have no idea if the code will work."
"Given that the OP has code that does not work, this would certainly be one ofthe first things to check..."
I am not sure on that one. if the code as he said worked on IAR and not on MDK, I would first check for compiler settings.
Something else that might affect the timing is reordering of instructions by the compiler to increase throughput.
I said: "you have no idea what [machine] code will be generated"
You said: "the same is true for any HLL code"
Yes! That is exactly the point!!
It is precisely because you have no idea what machine code will be generated from a HLL that, therefore, you cannot use a HLL to create specific timings!!
"Something else that might affect the timing"
tamir: good ones.
hopefully that's sufficient to convince andy that the execution duration of assembler delays is not possible to predict based on a) the code; and b) disable of the interrupt.
I could add a few more:
1) some chips can run on variable frequencies; 2) some 8051 chips can run on 1 cycle, 6 cycles or 12 cycles; 3) some chips can be user-configured on variable frequencies (those that use outside RC oscillators for example. but other possibilities exist too). ...
<QUOTE>the only (?) thing that can XXX</QUOTE>
<QUOTE>And of course YYY</QUOTE>
<QUOTE>Something else that ZZZ</QUOTE>
tapeer,
are you a fan of monty python? ever seen there won for the spanish inquisition?
please my freind, think thirst then right.
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