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what's the function of "AREGS"and "NOAREGS", can you provide me some sample, so that I could understand them clear. Are them still useful in current updated versions. In the manual it is said that with "NOAREGS" the function could be called by another functions using different register bank.
#pragma NOAREGS char add(char i) { return i+10; } void main(void) using 1 { ch = add(3); }
The discussed directives have, as far as I know, the meaning I have explained. NOAREGS disables absolute register access, while AREGS enables (but not forces) it. When enabled, the compiler decides whether to use it or not in a particular situation ("is it advantageous or not?"). It doesn't mean that the addressing method unconditionally changes to absolute register accesses in every case. See your compiled programs in my previous post. You obtain the same result either you use AREGS or NOAREGS, because in both these examples NOAREGS option "prevails". There is no reason for absolute register access there. That's why it is not used even if AREGS option is selected. "But in the manual it is said that with "NOAREGS" one function could be called by another functions using different register bank..." In my opinion it is confusing (if not even wrong) as far as passing parameters or return values in registers are concerned. I suppose you mean C51.pdf, page 24 (?): "This directive may be used for functions that are called from other functions using different register banks." or further, on page 124: "To make a function insensitive to the current register bank, the function must be compiled using the NOAREGS control directive. This would be useful for a function that was called from the main program and also from an interrupt function that uses a different register bank. Note: The Cx51 compiler does not and cannot detect a register bank mismatch between functions. Therefore, make sure that functions using alternate register banks call only other functions that do not assume a default register bank." and later, page 128: "Functions called from an interrupt procedure must function with the same register bank as the interrupt procedure. When the NOAREGS directive is not explicitly specified, the compiler may generate absolute register accesses using the register bank selected (by the using attribute or by the REGISTERBANK control) for that function. Unpredictable results may occur when a function assumes a register bank other than the one currently selected." Once more as to the function register bank in/dependance - for instance lets assume 2 functions: a) func1() compiled with NOAREGS pragma, containing "mov r7,a" instruction in its body, the resulting code is 0xFF b) func2() compiled with AREGS pragma, containing corresponding to the above "mov ar7,a" instruction in its body, the resulting codes are 0xF5 0x17 if register bank used at compile time was 2 if current register bank for both functions at calling time is, say, 1, then func1() will always write in R7 of the current register bank while func2() will write in absolute address 17H which is probably not the intention This is, among others, what they meant "To make a function insensitive to the current register bank..." In my opinion the RB independence concerns rather the body of the function than parameters or return values passed in registers. The directive "using" is suitable (my opinion) esp. with ISRoutines to prevent them from pushing big load onto the (very limited) stack. It is also useful for functions called from ISR. Using "using" :-) for other common functions seems to me a bit "violent". Best wishes
Since the compiler doesn't give a warning ,can I say this is a bug? We can send to keil?
Having a look at this note in Manual: "The Cx51 compiler does not and cannot detect a register bank mismatch between functions. Therefore, make sure that functions using alternate register banks call only other functions that do not assume a default register bank." I think it is true, so for the above mentioned warning the adjective "missing" is at least disputable. Realize that compile time and run time are different things and the compiler (compile time) doesn't necessarily know the actual RB of a function at run time in general. Sometimes it is up to you to judge and decide. That's why I suggested: don't use using directive with common functions unless you have a really important reason for it (ISR, etc.)
Please look at discussion thread 1807 http://www.keil.com/forum/docs/thread1807.asp