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mpfj
Joined: 09 Sep 2003
Posts: 95
Location: UK
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| Another table read bug |
 Posted: Fri Feb 20, 2004 6:45 am |
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Compiler version : 3v185
PIC type : 18F8720
I have a structure defined as follows ...
| Code: |
typedef struct {
int8 byte_count;
int1 multiple;
int1 broadcast;
} modbus_function_struct;
const modbus_function_struct modbus_function[MODBUS_NUM_FUNCTIONS] = {
{8, false, false}, // read coil status (digout readback)
{8, false, false}, // read input status
{8, false, false}, // read holding register (output register readback)
{8, false, false}, // read input register
{8, false, true}, // force single coil
{8, false, true}, // preset single register
{4, false, false}, // read exception status
{8, false, false}, // loopback diagnostic test
{0, false, false},
{0, false, false},
{0, false, false},
{0, false, false},
{0, false, false},
{0, false, false},
{7, true, true}, // force multiple coils
{7, true, true} // preset multiple registers
};
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The "const" function generated is as follows ...
| Code: |
0E84: MOVFF FF2,0E
0E88: BCF FF2.7
0E8A: CLRF FF7
0E8C: ADDLW A2
0E8E: MOVWF FF6
0E90: MOVLW 0E
0E92: ADDWFC FF7,F
0E94: MOVLW 00
0E96: MOVWF FF8
0E98: TBLRD*+
0E9A: MOVF FF5,W <------ here the result is placed in the WREG
0E9C: BTFSC 0E.7
0E9E: BSF FF2.7
0EA0: RETURN 0
0EA2: DATA 08,00
0EA4: DATA 08,00
0EA6: DATA 08,00
0EA8: DATA 08,00
0EAA: DATA 08,02
0EAC: DATA 08,02
0EAE: DATA 04,00
0EB0: DATA 08,00
0EB2: DATA 00,00
0EB4: DATA 00,00
0EB6: DATA 00,00
0EB8: DATA 00,00
0EBA: DATA 00,00
0EBC: DATA 00,00
0EBE: DATA 07,03
0EC0: DATA 07,03
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Note that the result of the table read is placed in the WREG.
Now, when I request "byte_count", the compiler produces the following ...
| Code: |
.................... // set message size
.................... message_size = modbus_function[modbus.func].byte_count;
AF0E: BCF FD8.0
AF10: RLCF x21,W
AF12: MOVLB C
AF14: CLRF x0D
AF16: MOVWF x0C
AF18: MOVLB 0
AF1A: MOVFF C0D,03
AF1E: MOVLB C
AF20: MOVF x0C,W
AF22: MOVLB 0
AF24: CALL 0E84
AF28: MOVWF 01
AF2A: MOVFF 01,C0B
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Note that after the CALL 0E84 instruction, the WREG is accessed, thus using the correct value.
*BUT* when I access one of the int1 values, e.g. "multiple", the following code is generated ...
| Code: |
.................... // are we expecting any additional bytes ??
.................... if (modbus_function[modbus.func].multiple) {
AF2E: BCF FD8.0
AF30: MOVLB A
AF32: RLCF x21,W
AF34: MOVLB C
AF36: CLRF x0D
AF38: MOVWF x0C
AF3A: MOVLW 01
AF3C: ADDWF x0C,W
AF3E: MOVWF 01
AF40: MOVLW 00
AF42: ADDWFC x0D,W
AF44: MOVWF 03
AF46: MOVF 01,W
AF48: MOVLB 0
AF4A: CALL 0E84
AF4E: CLRF 08
AF50: BTFSC 00.0
AF52: INCF 08,F
AF54: BTFSS 01.0
AF56: GOTO AF84
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As you might notice, after the CALL 0E84 instruction, absolutely *no* access to the WREG is made !!!! 
Am I missing something, or should I report this to CCS ?
Mark |
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mpfj
Joined: 09 Sep 2003
Posts: 95
Location: UK
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| Posted: Fri Feb 27, 2004 3:34 am |
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This has been fixed in 3v186 ...
... actually it hasn't !! They claim it has been, but the bug is still there !!
Oops ... |
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Neutone
Joined: 08 Sep 2003
Posts: 839
Location: Houston
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| Posted: Fri Feb 27, 2004 8:30 am |
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| I posted some code that does table reads not very long ago. It is also part of a MODBUS routine. It works fine. I suspect your problem is due in part to the syntax you are using. When recieving packets in MODBUS protocol there is a requirement that the bytes within the packet are not followed by a pause greater than 1.5 byte times between bytes. Simply counting bytes as the are recieved will not detect this and is more dificult to impliment. If you look at my other post you will see a working example of this. |
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mpfj
Joined: 09 Sep 2003
Posts: 95
Location: UK
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| Posted: Fri Feb 27, 2004 8:42 am |
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My modbus code works fine  And in most cases table reads work fine.
It is only when you have an array of structures (which contain int1 variables) that things go wrong.
Try compiling the following program and inspect the code generated for the last instruction ...
| Code: | #include <18F8720.h>
typedef struct {
int8 byte_count;
int1 multiple;
int1 broadcast;
} a_struct;
const a_struct a_function[16] = {
{8, false, false}, // read coil status (digout readback)
{8, false, false}, // read input status
};
void main() {
int8 i;
int1 j;
int8 k;
// init index
k = 0;
// here we read the int8 value
i = a_function[k].byte_count;
// here we read one of the int1 values
j = a_function[k].multiple;
}
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Notice how the table lookup routine returns its value in the WREG, but it's not used in the code. |
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