Subversion Repositories or1k

Originally by Chris Ziomkowski 

Brief introduction to using GDB based debugging with or1ksim

GDB uses the JTAG proxy server included in or1ksim to communicate

directly with the simulator. Only 1 connection is allowed to the

proxy server at a time. Attempting a second connection will terminate

the previous connection. This is very useful when the gdb or1k

process terminates abnormally (such as when you are debugging the

debugger.) In this case it is impossible to notify the JTAG server

that the socket has shut down, and therefore it will assume that a

new connection implies the termination of the previous process.

The or1ksim will start the JTAG proxy server on the port specified

for service "jtag". If such a service is not specified, the server

will choose a random port number. This behavior can be overridden by

specifying the port number to the simulator using the -srv option.

As an example, "sim -srv 9999" starts up the simulator with the

JTAG proxy server on port 9999. This behavior is useful for those

people who do not have root access and can not add services to

the config files (such as university students operating in a shared

environment.)

As the JTAG proxy server runs only if there is data available for

reading, there is very little resource usage consumed by this

capability. However, in certain instances where gdb is not being

utilized, it is possible to disable the JTAG proxy server

entirely.  This will recover the few cycles necessary for the

poll() system call. (Tests indicate this has a negligible to

non existant impact on speed, however your mileage may vary.)

This behavior can be achieved by starting the simulator with

the command "sim -nosrv."

At startup, the simulator will execute random commands, just as

a real chip would do performing in this environment if the memory

was not initialized. If it is desired to simulate a ROM or FLASH

environment, these can be approximated by using the -loadmem option

to the simulator. For example, to simulate a 32k flash at location

0x8000, the command "sim -loadmem@0x8000 " could be

used, where  represents the name of the initialization

file. If the optional '@0x8000' flag is left off of the loadmem

statement, then the load will occur at location 0. Several loadmem

flags can appear on the command line to simulate different

memory blocks.

It is also possible to initialize all RAM to a predefined value,

which is usually 0x00000000 or 0xFFFFFFFF. This would be equivalent

to what is normally observed in a real world environment. However,

specific sequences are possible in case this is necessary. Alternatively,

random values can be assigned to memory, to check the behavior of a

process under different conditions. All of these options can be

handled by the "-initmem" option of the simulator. The following

command would startup the simulator with all memory initialized to

"1":

sim -initmem 0xFFFFFFFF

while this command would generate random values:

sim -initmem random

Once the simulator is started, it will print out something like

the following:

> bash-2.03$ sim

> JTAG Proxy server started on port 42240

> Machine initialization...

> Data cache tag: physical

> Insn cache tag: physical

> BPB simulation on.

> BTIC simulation on.

> Clock cycle: 4 ns

> RAM: 0x0 to 0x7aa80 (490 KB)

>

> simdebug off, interactive prompt off

> Building automata... done, num uncovered: 0/216.

> Parsing operands data... done.

> Resetting 4 UART(s).

> UART0 has problems with RX file stream.

> Resetting Tick Timer.

> Resetting Power Management.

> Resetting PIC.

> Exception 0x100 (Reset): Iqueue[0].insn_addr: 0x0  Eff ADDR: 0x0

>  pc: 0x0  pcnext: 0x4

>

Note that because we did not specify a server port, a random

port (42240) was selected for us (The "jtag" service does not

exist on this machine). We will need this value to create the

connection URL for the target command. It is now possible to

debug a program with gdb as follows:

> bash-2.03$ gdb

> GNU gdb 5.0

> Copyright 2000 Free Software Foundation, Inc.

> GDB is free software, covered by the GNU General Public License, and you are

> welcome to change it and/or distribute copies of it under certain conditions.

> Type "show copying" to see the conditions.

> There is absolutely no warranty for GDB.  Type "show warranty" for details.

> This GDB was configured as "--host=sparc-sun-solaris2.7 --target=or32-rtems".

> (or1k) file "dhry.or32"

> Reading symbols from dhry.or32...done.

> (or1k) target jtag jtag://localhost:42240

> Remote or1k debugging using jtag://localhost:42240

> 0x0 in ?? ()

> (or1k) load dhry.or32

> Loading section .text, size 0x14fc lma 0x100

> Loading section .data, size 0x2804 lma 0x15fc

> Start address 0x100 , load size 15616

> Transfer rate: 124928 bits/sec, 488 bytes/write.

> (or1k) b main

> Breakpoint 1 at 0x51c: file dhry.c, line 176.

> (or1k) run

> Starting program: /usr3/home/chris/opencores/or1k/gdb-build/gdb/dhry.or32

>

> Breakpoint 1, main () at dhry.c:176

> 176       Next_Ptr_Glob = (Rec_Pointer) &x;

> (or1k)

The simulator window will have printed out the following, showing that

a breakpoint exception was asserted.

> Exception 0xd00 (Break): Iqueue[0].insn_addr: 0x51c  Eff ADDR: 0x0

> pc: 0x51c  pcnext: 0x520

Note that when the "run" command is given, the simulator will start

by jumping to the reset vector at location 0x100. You must start off

by placing a small bootloader at this location. A simple environment

capable of running C programs can be established by placing the

following code in a file called "start.s" and linking it to your

executable. As an example, the following will work. The file start.s

was derived from the output of a file start.c compiled by gcc:

or32-rtems-gcc -g -c -o start.o start.s

or32-rtems-gcc -g -c -DOR1K -o dhry.o dhry.c

or32-rtems-ld -Ttext 0x0 -o dhry.or32 start.o dhry.o

---------------------- CUT HERE -------------------------

# file start.s

.file   "start.s"

# This is the general purpose start routine. It

# sets up the stack register, and jumps to the

# _main program location. It should be linked at

# the start of all programs.

.text

        .align  4

        .org    0x100                   # The reset routine goes at 0x100

.proc _rst

        .def    _rst

        .val    _rst

        .scl    2

        .type   041

        .endef

        .global _rst

_rst:

        .def    .bf

        .val    .

        .scl    101

        .endef

        l.addi          r1,r0,0x7f00    # Set STACK to value 0x7f00

        l.addi          r2,r1,0x0       # FRAME and STACK are the same

        l.mfspr         r3,r0,17        # Get SR value

        l.ori           r3,r3,2         # Set exception enable bit

        l.jal           _main           # Jump to main routine

        l.mtspr         r0,r3,17        # Enable exceptions (DELAY SLOT)

.endproc _rst

        .def    _rst

        .val    .

        .scl    -1

        .endef

        .org    0xFFC

        l.nop                           # Guarantee the exception vector space

                                        # does not have general purpose code

# C code starts at 0x1000

---------------------- CUT HERE -------------------------