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C166 Var verses immediate as index value

Hi All, I'm having a real hard time coming up with a reason why using a local var as an index into a struct fails but that same line with an immediate value specified works properly. Here's what I mean..

void main(void)
	{
	unsigned char cTemp, cValue;

// Do whats required to get under way.
//----------------------------------------------------------------------------
 	MAIN_System_Init();


// Endless While loop that the micro runs forever (hopefully).
//----------------------------------------------------------------------------
	while(gcTRUE)
		{
		cValue = 0x0C;

		cTemp = *port[0x0C].lsr;
		cTemp = *port[0x0C].txrx;

		cTemp = *port[cValue].lsr;
		cTemp = *port[cValue].txrx;

		}
	}

The first two reads to cTemp work properly (with the value 0x0C specified) but the following two reads using the cValue variable as the index fail? BTW, The reason that I say they fail is that the reads should generate an external bus read to a uart register. The first two reads generate a chip select and the second two do not. I've tried changing compiler optimizations and options but I'm running out of ideas. I'm using ver 4.20c of the C compiler and version 4.20 of most everything else. Any suggestions would be really appreciated. Thanks. ~Tim

Parents

0 Jon Ward over 23 years ago in reply to Mik Kleshov

I just compiled the following:

unsigned char lsr = 12;
unsigned char txrx = 34;

struct ct_st
  {
  unsigned char *lsr;
  unsigned char *txrx;
  };


volatile struct ct_st port [] =
  {
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
  };


void main(void)
	{
	unsigned char  cTemp, cValue;

// Do whats required to get under way.
//----------------------------------------------------------------------------
// 	MAIN_System_Init();


// Endless While loop that the micro runs forever (hopefully).
//----------------------------------------------------------------------------
	while(1)
		{
		cValue = 0x0C;

		cTemp = *port[0x0C].lsr;
		cTemp = *port[0x0C].txrx;

		cTemp = *port[cValue].lsr;
		cTemp = *port[cValue].txrx;

		}
	}

and got the following output:

             ; FUNCTION main (BEGIN  RMASK = @0x4022)
                                           ; SOURCE LINE # 33
                                           ; SOURCE LINE # 34
                                           ; SOURCE LINE # 44
0000         ?C0003:
                                           ; SOURCE LINE # 46
                                           ; SOURCE LINE # 48
0000 F2F13000 R    MOV       R1,port+030H
0004 A9A1          MOVB      RL5,[R1]
;---- Variable 'cTemp' assigned to Register 'RL5' ----
                                           ; SOURCE LINE # 49
0006 F2F13200 R    MOV       R1,port+032H
000A A9A1          MOVB      RL5,[R1]
                                           ; SOURCE LINE # 51
000C F2F13000 R    MOV       R1,port+030H
0010 A9A1          MOVB      RL5,[R1]
                                           ; SOURCE LINE # 52
0012 F2F13200 R    MOV       R1,port+032H
0016 A9A1          MOVB      RL5,[R1]
                                           ; SOURCE LINE # 54
0018 0DF3          JMPR      cc_UC,?C0003
             ; FUNCTION main (END    RMASK = @0x4022)

These look AOK to me.

Jon

Reply

0 Jon Ward over 23 years ago in reply to Mik Kleshov

I just compiled the following:

unsigned char lsr = 12;
unsigned char txrx = 34;

struct ct_st
  {
  unsigned char *lsr;
  unsigned char *txrx;
  };


volatile struct ct_st port [] =
  {
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
    { &lsr, &txrx },
  };


void main(void)
	{
	unsigned char  cTemp, cValue;

// Do whats required to get under way.
//----------------------------------------------------------------------------
// 	MAIN_System_Init();


// Endless While loop that the micro runs forever (hopefully).
//----------------------------------------------------------------------------
	while(1)
		{
		cValue = 0x0C;

		cTemp = *port[0x0C].lsr;
		cTemp = *port[0x0C].txrx;

		cTemp = *port[cValue].lsr;
		cTemp = *port[cValue].txrx;

		}
	}

and got the following output:

             ; FUNCTION main (BEGIN  RMASK = @0x4022)
                                           ; SOURCE LINE # 33
                                           ; SOURCE LINE # 34
                                           ; SOURCE LINE # 44
0000         ?C0003:
                                           ; SOURCE LINE # 46
                                           ; SOURCE LINE # 48
0000 F2F13000 R    MOV       R1,port+030H
0004 A9A1          MOVB      RL5,[R1]
;---- Variable 'cTemp' assigned to Register 'RL5' ----
                                           ; SOURCE LINE # 49
0006 F2F13200 R    MOV       R1,port+032H
000A A9A1          MOVB      RL5,[R1]
                                           ; SOURCE LINE # 51
000C F2F13000 R    MOV       R1,port+030H
0010 A9A1          MOVB      RL5,[R1]
                                           ; SOURCE LINE # 52
0012 F2F13200 R    MOV       R1,port+032H
0016 A9A1          MOVB      RL5,[R1]
                                           ; SOURCE LINE # 54
0018 0DF3          JMPR      cc_UC,?C0003
             ; FUNCTION main (END    RMASK = @0x4022)

These look AOK to me.

Jon

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