The OpenRISC cpu, simulator and toolchain provide a full debugging environment with gdb and OpenOCD. At a low level this is provided with adv_debug_sys which provides jtag interface for OpenOCD to talk to. Much can be done directly in OpenOCD. But for a full debug environments we recommend GDB. GDB communicates with OpenOCD as a remote target and provides a familiar debugging environment for programmers.
OpenOCD requires a configuration file to start up. The configuration files specify the chips details (jtag tap) and the details of the interface we are using.
You can also define init and reset hooks to perform extra operations to
propertly refresh and initialize your system. See details on the OpenOCD user
guide on
Target Events.
# command for starting openocd when connecting to openrisc on the altera de0 nano
# -s specifies the files source path
# -f specifies config files to load
OPENOCD={location of openocd}
openocd -s $OPENOCD/scripts -f interface/altera-usb-blaster.cfg -f board/or1k_generic.cfg
Open On-Chip Debugger 0.10.0-dev-00247-g73b676c (2016-03-03-15:18)
Licensed under GNU GPL v2
...
Info : adv debug unit is configured with option ADBG_USE_HISPEED
Info : adv debug unit is configured with option ENABLE_JSP_MULTI
Info : adv debug unit is configured with option ENABLE_JSP_SERVER
Halting processor
or1200.cpu: target state: halted
Chip is or1200.cpu, Endian: big, type: or1k
Target ready...
Once started OpenOCD will start listening on 2 TCP ports
- 4444 - OpenOCD telnet interface
- 3333 - GDB target interface
You can connect to the 4444 telnet interface and do things such as follows
# Telnet to OpenOCD
telnet localhost 4444
# Initialize the init script
init
# Perform a reset
reset
requesting target halt and executing a soft reset
# Halt the cpu
halt
# Load an image (the image location is relative to the working directory of openocd)
load_image tutorials/de0_nano/hello.elf
# Set a register (in this case next program counter)
# OpenRISC reset vector is 0x100 so this causes the cpu to jump
# to the start of our program which should start at 0x100
reg npc 0x100
# Resume execution after a halt
resume
# For loading a linux image you can do it all at one time.
# Notice here we also reset r3 which linux uses as a bootargs
# vector.
halt; load_image vmlinux; reg r3 0; reg npc 0x100; resume
# Inspect registers
reg npc
npc (/32): 0x00006BC0
# Inspect all registers
reg
===== OpenRISC 1000 registers:
(0) r0 (/32)
(1) r1 (/32)
(2) r2 (/32)
(3) r3 (/32)
...
(2212) itlbw3mr126 (/32)
(2213) itlbw3tr126 (/32)
(2214) dtlbw3mr127 (/32)
(2215) dtlbw3tr127 (/32)
(2216) itlbw3mr127 (/32)
(2217) itlbw3tr127 (/32)
(2218) rtest (/32)
# Inspecting memory
mdw 0x100
0x00000100: 18000000
# Finish up
exit
When we run GDB we do remote debugging
# Starting up gdb (with a remote target)
or1k-elf-gdb hello.elf --eval-command='target remote localhost:3333'
# Issue any OpenOCD commands by prefixing with monitor
monitor init
monitor reset
# Loading an image
load
Loading section .vectors, size 0x2000 lma 0x0
Loading section .init, size 0x28 lma 0x2000
Loading section .text, size 0x4da0 lma 0x2028
Loading section .fini, size 0x1c lma 0x6dc8
Loading section .rodata, size 0x1c lma 0x6de4
Loading section .eh_frame, size 0x4 lma 0x8e00
Loading section .ctors, size 0x8 lma 0x8e04
Loading section .dtors, size 0x8 lma 0x8e0c
Loading section .jcr, size 0x4 lma 0x8e14
Loading section .data, size 0xc74 lma 0x8e18
Start address 0x100, load size 31372
Transfer rate: 329 KB/sec, 2091 bytes/write.
# List our program (if its c)
l
1 #include <stdio.h>
2
3 int main(int argc, char* argv[]) {
4 printf("Hello World!\n");
5 return 0;
6 }
# See actual assembly
disas
Dump of assembler code for function main:
0x00002398 <+0>: l.sw -8(r1),r2
0x0000239c <+4>: l.addi r2,r1,0
0x000023a0 <+8>: l.sw -4(r1),r9
0x000023a4 <+12>: l.addi r1,r1,-16
0x000023a8 <+16>: l.sw -12(r2),r3
0x000023ac <+20>: l.sw -16(r2),r4
=> 0x000023b0 <+24>: l.movhi r3,0x0
0x000023b4 <+28>: l.ori r3,r3,0x6de4
0x000023b8 <+32>: l.jal 0x252c <puts>
0x000023bc <+36>: l.nop 0x0
0x000023c0 <+40>: l.addi r3,r0,0
0x000023c4 <+44>: l.ori r11,r3,0x0
0x000023c8 <+48>: l.ori r1,r2,0x0
0x000023cc <+52>: l.lwz r2,-8(r1)
0x000023d0 <+56>: l.lwz r9,-4(r1)
0x000023d4 <+60>: l.jr r9
0x000023d8 <+64>: l.nop 0x0
End of assembler dump.
# Inspecing Registers
## Inspecting a single register
info reg r1
r1 0x1ffdff0 33546224
## Listing all general registers.
info reg
r0 0x0 0 (always zero)
r1 0x1ffdff0 33546224 (stack pointer)
r2 0x1ffe000 33546240 (frame pointer)
r3 0x0 0
r4 0x0 0
r5 0x0 0
r6 0xffffffc3 -61
r7 0x39080 233600
r8 0x1c2000 1843200
r9 0x2130 8496 (return address)
r10 0x0 0
r11 0x0 0
r12 0x9a8c 39564
r13 0x5 5
r14 0x20 32
r15 0x80000000 -2147483648
r16 0x0 0
r17 0x0 0
r18 0x0 0
r19 0x0 0
r20 0x0 0
r21 0x0 0
r22 0x22 34
r23 0x0 0
r24 0x0 0
r25 0x0 0
r26 0x0 0
r27 0x0 0
r28 0x0 0
r29 0x0 0
r30 0x0 0
r31 0x0 0
## Listing all special register groups
maint print reggroups
Group Type
system user
dmmu user
immu user
dcache user
icache user
mac user
debug user
perf user
power user
pic user
timer user
## Listing registers in a register group
info reg system
vr 0x10000040 268435520
upr 0x55f 1375
cpucfgr 0x3820 14368
dmmucfgr 0x18 24
immucfgr 0x18 24
dccfgr 0x24c1 9409
iccfgr 0x4c1 1217
dcfgr 0x0 0
# Inspecing Memory
## print 32 hex words of memory contents at location
x/10xw 0x1ffdff0
0x1ffdff0: 0x00000000 0x00000000 0x01ffe000 0x00002130
0x1ffe000: 0xc1fffe92 0x00000004 0xc1fff930 0xc1ffe034
0x1ffe010: 0x00000000 0x00000000
## print 3 instructions at location
x/3ih 0x100
0x100 <_or1k_reset>: l.movhi r0,0x0
0x104 <_or1k_reset+4>: l.movhi r1,0x0
0x108 <_or1k_reset+8>: l.movhi r2,0x0
These commands and further reading should get you started.
- http://openocd.org/doc/html/ - OpenOCD User Guide
- http://www.fpga4fun.com/JTAG2.html - How JTAG works
- https://sourceware.org/gdb/onlinedocs/gdb/ - Debugging with GDB