I am trying to debug the exact bus error on the m4 cortex chip. The board is teensy 3.1 with freescale MK20DX256VLH7. The error occurs only when I actually send characters with uart and leads to a forced hard error, because I do not have error handlers in the buffer and memory. The error occurs after a random amount of time between 1 second and 1 minute when sending 30 integers per second with uart. Also, when I print the values in binary format, not in uartPutInt (), but in the uartPutBin () function, an error does not occur.
I hacked teensy, so I can use SWD debugging. I use toolchain for gb, gdb, non-eabi.
I tried to double the size of the stack, but that does not help. I tried different itoa () approaches, does not help.
The full code can be obtained here:
https://github.com/paulusbrand/tricopter
The problem arises in the uartPutInt () function, its not the most beautiful function, but I tried different approaches, and this is easiest to debug and understand.
original:
void uartPutInt(int32_t data) {
char buf[16] = {0};
uint32_t tmpData;
uint8_t neg = 0;
int8_t tmp = 0;
if(data<0) {
tmpData = -data;
neg=1;
}
else {
tmpData = data;
}
while(tmpData) {
uint8_t num = tmpData % 10;
buf[tmp++]=num+48;
tmpData/=10;
}
if(neg) {
buf[tmp++] = 45;
}
while(tmp>=0) {
uartPutChar(buf[tmp--]);
}
}
a new version:
void uartPutInt(int32_t data) {
char buf[16] = {0};
uint32_t tmpData;
uint8_t neg = 0;
int8_t tmp = 0;
if(data<0) {
tmpData = -data;
neg=1;
}
else {
tmpData = data;
}
do {
uint8_t num = tmpData % 10;
buf[tmp++]=num+'0';
tmpData/=10;
} while(tmpData);
if(neg) {
buf[tmp++] = '-';
}
while(tmp>0) {
uartPutChar(buf[--tmp]);
}
}
When a bus error occurs, I check the CFSR register in the SCB and find the exact bus error and valid BFAR.
The value of BFAR and therefore the problem memory address is 0x01007fd2. This, as far as I can tell, is in the area of memory code, but far beyond the code. I'm not quite sure what to do with this number.
The PC program counter when an error occurs is 0x1033. What is in the uartPutInt () function. Understand below.
00000f6c <uartPutInt>:
f6c: b580 push {r7, lr}
f6e: b088 sub sp, #32
f70: af00 add r7, sp, #0
f72: 6078 str r0, [r7, #4]
f74: f107 0308 add.w r3, r7, #8
f78: 2200 movs r2, #0
f7a: 601a str r2, [r3, #0]
f7c: 3304 adds r3, #4
f7e: 2200 movs r2, #0
f80: 601a str r2, [r3, #0]
f82: 3304 adds r3, #4
f84: 2200 movs r2, #0
f86: 601a str r2, [r3, #0]
f88: 3304 adds r3, #4
f8a: 2200 movs r2, #0
f8c: 601a str r2, [r3, #0]
f8e: 3304 adds r3, #4
f90: 2300 movs r3, #0
f92: 76fb strb r3, [r7, #27]
f94: 687b ldr r3, [r7, #4]
f96: 2b00 cmp r3, #0
f98: da05 bge.n fa6 <uartPutInt+0x3a>
f9a: 687b ldr r3, [r7, #4]
f9c: 425b negs r3, r3
f9e: 61fb str r3, [r7, #28]
fa0: 2301 movs r3, #1
fa2: 76fb strb r3, [r7, #27]
fa4: e001 b.n faa <uartPutInt+0x3e>
fa6: 687b ldr r3, [r7, #4]
fa8: 61fb str r3, [r7, #28]
faa: e01f b.n fec <uartPutInt+0x80>
fac: 69f9 ldr r1, [r7, #28]
fae: 4b23 ldr r3, [pc, #140] ; (103c <uartPutInt+0xd0>)
fb0: fba3 2301 umull r2, r3, r3, r1
fb4: 08da lsrs r2, r3, #3
fb6: 4613 mov r3, r2
fb8: 009b lsls r3, r3, #2
fba: 4413 add r3, r2
fbc: 005b lsls r3, r3, #1
fbe: 1aca subs r2, r1, r3
fc0: 4613 mov r3, r2
fc2: 767b strb r3, [r7, #25]
fc4: 7eba ldrb r2, [r7, #26]
fc6: b2d3 uxtb r3, r2
fc8: 3301 adds r3, #1
fca: b2db uxtb r3, r3
fcc: 76bb strb r3, [r7, #26]
fce: b253 sxtb r3, r2
fd0: 7e7a ldrb r2, [r7, #25]
fd2: 3230 adds r2, #48 ; 0x30
fd4: b2d2 uxtb r2, r2
fd6: f107 0120 add.w r1, r7, #32
fda: 440b add r3, r1
fdc: f803 2c18 strb.w r2, [r3, #-24]
fe0: 69fb ldr r3, [r7, #28]
fe2: 4a16 ldr r2, [pc, #88] ; (103c <uartPutInt+0xd0>)
fe4: fba2 2303 umull r2, r3, r2, r3
fe8: 08db lsrs r3, r3, #3
fea: 61fb str r3, [r7, #28]
fec: 69fb ldr r3, [r7, #28]
fee: 2b00 cmp r3, #0
ff0: d1dc bne.n fac <uartPutInt+0x40>
ff2: 7efb ldrb r3, [r7, #27]
ff4: 2b00 cmp r3, #0
ff6: d00b beq.n 1010 <uartPutInt+0xa4>
ff8: 7eba ldrb r2, [r7, #26]
ffa: b2d3 uxtb r3, r2
ffc: 3301 adds r3, #1
ffe: b2db uxtb r3, r3
1000: 76bb strb r3, [r7, #26]
1002: b253 sxtb r3, r2
1004: f107 0220 add.w r2, r7, #32
1008: 4413 add r3, r2
100a: 222d movs r2, #45 ; 0x2d
100c: f803 2c18 strb.w r2, [r3, #-24]
1010: e00d b.n 102e <uartPutInt+0xc2>
1012: 7eba ldrb r2, [r7, #26]
1014: b2d3 uxtb r3, r2
1016: 3b01 subs r3, #1
1018: b2db uxtb r3, r3
101a: 76bb strb r3, [r7, #26]
101c: b253 sxtb r3, r2
101e: f107 0220 add.w r2, r7, #32
1022: 4413 add r3, r2
1024: f813 3c18 ldrb.w r3, [r3, #-24]
1028: 4618 mov r0, r3
102a: f7ff ff87 bl f3c <uartPutChar>
102e: f997 301a ldrsb.w r3, [r7, #26]
1032: 2b00 cmp r3, #0
1034: daed bge.n 1012 <uartPutInt+0xa6>
1036: 3720 adds r7, #32
1038: 46bd mov sp, r7
103a: bd80 pop {r7, pc}
103c: cccccccd stclgt 12, cr12, [ip], {205} ; 0xcd
Can someone please help me with this?
Thank!