NOAREG & AREG,

Still I am confused with Cole's words because the absolute addresses cannot be reliably computed at compile time.The following word is from Chapter 2,Cx51 Compiler User's Guide:

2
stmt level source
1 extern char func ();
2 char k;
3
4 #pragma NOAREGS
5 noaregfunc () {
6 1 k = func () + func ();
7 1 }
8
9 #pragma AREGS
10 aregfunc () {
11 1 k = func () + func ();
12 1 }
; FUNCTION noaregfunc (BEGIN)
; SOURCE LINE # 6
0000 120000 E LCALL func
0003 EF MOV A,R7
0004 C0E0 PUSH ACC
0006 120000 E LCALL func
0009 D0E0 POP ACC
000B 2F ADD A,R7
000C F500 R MOV k,A
; SOURCE LINE # 7
000E 22 RET
; FUNCTION noaregfunc (END)
; FUNCTION aregfunc (BEGIN)
; SOURCE LINE # 11
0000 120000 E LCALL func
0003 C007 PUSH AR7
0005 120000 E LCALL func
0008 D0E0 POP ACC
000A 2F ADD A,R7
000B F500 R MOV k,A
; SOURCE LINE # 12
000D 22 RET
; FUNCTION aregfunc (END)

push AR7

Still I am confused with Cole's words because the absolute addresses cannot be reliably computed at compile time.The following word is from Chapter 2,Cx51 Compiler User's Guide:

2
stmt level source
1 extern char func ();
2 char k;
3
4 #pragma NOAREGS
5 noaregfunc () {
6 1 k = func () + func ();
7 1 }
8
9 #pragma AREGS
10 aregfunc () {
11 1 k = func () + func ();
12 1 }
; FUNCTION noaregfunc (BEGIN)
; SOURCE LINE # 6
0000 120000 E LCALL func
0003 EF MOV A,R7
0004 C0E0 PUSH ACC
0006 120000 E LCALL func
0009 D0E0 POP ACC
000B 2F ADD A,R7
000C F500 R MOV k,A
; SOURCE LINE # 7
000E 22 RET
; FUNCTION noaregfunc (END)
; FUNCTION aregfunc (BEGIN)
; SOURCE LINE # 11
0000 120000 E LCALL func
0003 C007 PUSH AR7
0005 120000 E LCALL func
0008 D0E0 POP ACC
000A 2F ADD A,R7
000B F500 R MOV k,A
; SOURCE LINE # 12
000D 22 RET
; FUNCTION aregfunc (END)

push AR7

Do you mean that push AR7 is not reliable because the AR7 isn't reliably computed at compile time?

AR7 is the absolute address of register R7 in one particular register bank - could be one of four possibilities depending on of x in the preceeding "USING x". Each possible direct address for R7 is unique.

When a function is called, any of the four possible register banks could be selected at that instant and the compiler cannot predict which it will be.

Will the direction #pragma REGISTERBANK(x) apply only for the function that follows this statement, or will it apply untill a new REGISTERBANK direction will be stated ?

In the following example:

#pragma REGISTERBANK(3)
void func1 (void)
{
 ...
 ...
}


void func2 (void)
{
 ...
 ...
}

See: http://www.keil.com/support/man/docs/c51/c51_registerbank.htm

(The REGISTERBANK directive selects which register bank to use for subsequent functions).