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.
"when you write in assembler you can see what the instruction sequence is."
you have that with HLLs too: if not at the time of writing the (HLL) code but certainly after the compilation and having looked at the disassembly. I remember counting instructions and comparing various branches for TV signal generator code, :).
any (almost all?) "software" based delays run the risk of being non-predictable. the "non-predictability" is certainly bigger with HLL than it is with assembly - which I suspect is what you were trying to say.
fortunately, in most applications, we don't need (absolutely) precise delays, or we tolerate certain degree of timing un-predictability. Obviously, the bigger your tolerance for in-precision, the more likely a HLL delay solution will fit your bill.
so I think it is too extreme to base one's decision to use HLL or assembly delay routines on the ability to predict their duration.
"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...
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.
"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")