Hello all,
I hope someone can help me with a strange problem I have.
What I see is that there is a problem with my stack, I check if the 2 bytes
at __bss_end and __bss_end + 1 have a specific value, which I put in them,
so I can detect stack overflows in my application. I have a piece of code
that will generate a stack problem depending on if I enable or disable a
while loop in that piece of code.
The code is :
while (app_TXIncomming != 0) {
} /* while */
configMsg = &app_RS232_TX_Buffers [app_TXIncomming];
if (!configMsg->BufferFull) {
/* There is free space, so create the message
*/
/* We will send NoConfig_ind messages to the
base CPU and the
* base Extender, because we don't know what
is in the
* basestation */
app_GenAddress.NetworkID =
NETWORK_ID_BROADCAST;
app_GenAddress.DeviceID =
DEVICE_ID_BROADCAST;
switch (stepStateNoConfig) {
case app_NOCONFIGSTEP_BASECPU:
app_GenAddress.DeviceType =
DEVTYPE_WS_BASE_CPU;
stepStateNoConfig =
app_NOCONFIGSTEP_EXTENDER;
break;
case app_NOCONFIGSTEP_EXTENDER:
app_GenAddress.DeviceType =
DEVTYPE_WS_EXTENDER;
stepStateNoConfig =
app_NOCONFIGSTEP_BASECPU;
break;
} /* switch */
//WISP_Put_Flags (configMsg, 0);
WISP_Put_Flags (configMsg, 0);
This code is part of a larger function.
A little explanation of the code:
configMsg pointer to the same type as the array
app_RS232_TX_Buffers
app_TXIncomming the index of the next buffer that I can use to
create a message that must be transmitted via the RS-232 port.
app_GenAddress a structure that can contain an address as we use
it
What I see no is that when the while loop at the beginning is compiled into
the code, everything is running OK, but when I comment it out, so it is not
in de code, the stack check fails, indicating that __bss_end and __bss_end +
1 no longer have the specific test values.
Below is the part of the .lst file for both cases.
With commented out while loop:
--------------------------------------
585 lds r24,app_TXIncomming
586 mul r24,r16
587 012a 84E0 movw r30,r0
588 012c 0E94 0000 clr r1
589 0130 00C0 subi r30,lo8(-(app_RS232_TX_Buffers))
590 sbci
r31,hi8(-(app_RS232_TX_Buffers))
592 .LM51:
593 0132 8091 0000 ldd r24,Z+1
594 0136 809F tst r24
595 0138 F001 brne .L20
597 013c E050 .LM52:
598 013e F040 sts app_GenAddress,__zero_reg__
600 .LM53:
601 0140 8181 sts
(app_GenAddress+2)+1,__zero_reg__
602 0142 8823 sts app_GenAddress+2,__zero_reg__
604 .LM54:
605 tst r17
606 0146 1092 0000 brne .L45
608 .LM55:
609 014a 1092 0000 sts app_GenAddress+1,r15
610 014e 1092 0000 ldi r17,lo8(1)
611 .L21:
613 0152 1123 .LM56:
614 0154 01F4 movw r24,r30
615 ldi r22,lo8(0)
616 call WISP_Put_Flags
With while loop in place:
-----------------------------
583 0126 0E94 0000 .LM50:
584 012a 00C0 lds r24,app_RS232_TX_Buffers+1
585 tst r24
586 012c 8091 0000 brne .L21
588 .LM51:
589 sts
app_GenAddress,__zero_reg__
591 0132 01F4 .LM52:
592 sts
(app_GenAddress+2)+1,__zero_reg__
593 sts
app_GenAddress+2,__zero_reg__
595 0138 8823 .LM53:
596 013a 01F4 tst r17
597 brne .L47
599 013c 1092 0000 .LM54:
600 sts app_GenAddress+1,r16
601 ldi r17,lo8(1)
602 0140 1092 0000 .L22:
604 .LM55:
605 ldi
r24,lo8(app_RS232_TX_Buffers)
606 0148 1123 ldi r25,hi8(app_RS232_TX_Buffers)
607 014a 01F4 ldi r22,lo8(0)
608 call WISP_Put_Flags
When I leave the while loop in the code, the code is smaller than without
the while loop, which seems strange, because the while loop has no effect on
the actual code.
I am using the latest WinAVR with AVR-GCC 4.3.3 at the moment, but I started
with the previous version AVR-GCC 4.3.2, which did the exact same thing.
Optimisation is set to size, I am using an ATMega168. Optimisations that I
use are :
-mcall-prologues, -ffunction-sections, -fdata-sections,
-fno-free-loop-optimize, -fno-inline, -fno-tree-scev-cprop, -fpack-struct
This seems to give me the smallest code, which is what I need, because I am
almost at the limit of code space.
The most simple solution would be to just keep the while loop in the code,
but since it does nothing, it is a strange piece of code to keep in my
application and what other parts of the code would have similar problems and
would also require something like this ?!
Does anyone know what is going wrong here ?
Greetings,
Han
---
Han Hoekstra
Software Engineer
Wireless Value B.V.
Waanderweg 30a
7812 HZ Emmen
Tel: +31-591-633200
Fax: +31-591-631197
Web: <http://www.wirelessvalue.nl> www.wirelessvalue.nl
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