cc65/doc/sim65.sgml

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<article>

<title>sim65 Users Guide
<author><url url="mailto:polluks@sdf.lonestar.org" name="Stefan A. Haubenthal">,<newline>
<url url="mailto:bbbradsmith@users.noreply.github.com" name="Brad Smith">


<abstract>
sim65 is a simulator for 6502 and 65C02 CPUs. It allows to test target
independent code.
</abstract>

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<toc>

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<sect>Overview<p>


sim65 is used as part of the toolchain to test 6502 or 65C02 code.
The binary to test should be compiled with <tt/--target sim6502/ or <tt/--target sim65c02/.


<sect>Usage<p>

The simulator is called as follows:

<tscreen><verb>
        Usage: sim65 [options] file [arguments]
        Short options:
          -h                    Help (this text)
          -c                    Print amount of executed CPU cycles
          -v                    Increase verbosity
          -V                    Print the simulator version number
          -x <num>              Exit simulator after <num> cycles

        Long options:
          --help                Help (this text)
          --cycles              Print amount of executed CPU cycles
          --verbose             Increase verbosity
          --version             Print the simulator version number
</verb></tscreen>

sim65 will exit with the error code of the simulated program,
which is limited to an 8-bit result 0-255.

An error in sim65, like bad arguments or an internal problem will exit with <tt/1/.

A timeout from <tt/-x/ will exit with <tt/2/.


<sect1>Command line options in detail<p>

Here is a description of all the command line options:

<descrip>

  <tag><tt>-h, --help</tt></tag>

  Print the short option summary shown above.


  <tag><tt>-c, --cycles</tt></tag>

  Print the number of executed CPU cycles when the program terminates.
  The cycles for the final "<tt>jmp exit</tt>" are not included in this
  count.


  <tag><tt>-v, --verbose</tt></tag>

  Increase the simulator verbosity.


  <tag><tt>-V, --version</tt></tag>

  Print the version number of the utility. When submitting a bug report,
  please include the operating system you're using, and the compiler
  version.


  <tag><tt>-x num</tt></tag>

  Exit simulator after num cycles.
</descrip>


<sect>Input and output<p>

The simulator will read one binary file per invocation and can log the
program loading and paravirtualization calls to stderr.

Example output for the command
<tscreen><verb>
sim65 --verbose --verbose samples/gunzip65
</verb></tscreen>
<tscreen><verb>
Loaded 'samples/gunzip65' at $0200-$151F
PVWrite ($0001, $13C9, $000F)
GZIP file name:PVWrite ($0001, $151F, $0001)

PVRead ($0000, $FFD7, $0001)
PVOpen ("", $0001)
PVRead ($0003, $1520, $6590)
PVClose ($0003)
PVWrite ($0001, $13D9, $000F)
Not GZIP formatPVWrite ($0001, $151F, $0001)

PVExit ($01)
</verb></tscreen>


<sect>Creating a Test in C<p>

For a C test linked with <tt/--target sim6502/ and the <tt/sim6502.lib/ library,
command line arguments to <tt/sim65/ will be passed to <tt/main/,
and the return value from <tt/main/ will become sim65's exit code.
The <tt/stdlib.h/ <tt/exit/ function may also be used to terminate with an exit code.

Exit codes are limited to an unsigned 8 bit value. (E.g. returning -1 will give an exit code of 255.)

The standard C library high level file input and output is functional.
A sim65 application can be written like a command line application,
providing command line arguments to <tt/main/ and using the <tt/stdio.h/ interfaces
to interact with the console or access files.

Internally, file input and output is provided at a lower level by
a set of built-in paravirtualization functions (see <ref id="paravirt-internal" name="below">).

Example:

<tscreen><verb>
#include <stdio.h>
int main()
{
    printf("Hello!\n");
    return 5;
}

// Build and run:
//   cl65 -t sim6502 -o example.prg example.c
//   sim65 example.prg

// Build and run, separate steps:
//   cc65 -t sim6502 -o example.s example.c
//   ca65 -t sim6502 -o example.o example.s
//   ld65 -t sim6502 -o example.prg example.o sim6502.lib
//   sim65 example.prg
</verb></tscreen>

<sect>Creating a Test in Assembly<p>

Though a C test may also link with assembly code,
a pure assembly test can also be created.

Link with <tt/--target sim6502/ or <tt/--target sim65c02/ and the corresponding library,
define and export <tt/_main/ as an entry point,
and the sim65 library provides two ways to return an 8-bit exit code:

<itemize>

<item>Return from <tt/_main/ with the exit code in <tt/A/.

<item><tt/jmp exit/ with the code in <tt/A/. (<tt/.import exit/ from the sim65 library.)

</itemize>

Example:

<tscreen><verb>
.export _main
_main:
    lda #5
    rts

; Build and run:
;   cl65 -t sim6502 -o example.prg example.s
;   sim65 example.prg

; Build and run, separate steps:
;   ca65 -t sim6502 -o example.o example.s
;   ld65 -t sim6502 -o example.prg example.o sim6502.lib
;   sim65 example.prg
</verb></tscreen>

Internally, the binary program file has a 12 byte header provided by the library:

<itemize>

<item>5 byte <bf/signature/: <tt/$73, $69, $6D, $36, $35/ or <tt/'sim65'/

<item>1 byte <bf/version/: <tt/2/

<item>1 byte <bf/CPU type/: <tt/0/ = 6502, <tt/1/ = 65C02

<item>1 byte <bf/sp address/: the zero page address of the C parameter stack pointer <tt/sp/ used by the paravirtualization functions

<item>1 word <bf/load address/: where to load the data from the file into memory (default: <tt/$0200/)

<item>1 word <bf/reset address/: specifies where to begin execution after loading (default: <tt/$0200/)

</itemize>

Other internal details:

<itemize>

<item>The entire 64 kilobyte address space is writeable RAM.
Aside from the loaded binary, the reset vector at <tt/$FFFC/ will be
pre-loaded with the given <bf/reset address/.

<item>The <tt/exit/ address is <tt/$FFF9/.
Jumping to this address will terminate execution with the A register value as an exit code.

<label id="paravirt-internal">
<item>Several bytes immediately below the vector table are reserved for paravirtualization functions.
Except for <tt/exit/, a <tt/JSR/ to one of these addresses will return immediately after performing a special function.
These use cc65 calling conventions, and are intended for use with the sim65 target C library.

<item><tt/IRQ/ and <tt/NMI/ events will not be generated, though <tt/BRK/
can be used if the IRQ vector at <tt/$FFFE/ is manually prepared by the test code.

<item>The <tt/sim6502/ or <tt/sim65c02/ targets provide a default configuration,
but if customization is needed <tt/sim6502.cfg/ or <tt/sim65c02.cfg/ might be used as a template.

</itemize>

<sect>Counter peripheral

<p>The sim65 simulator supports a memory-mapped counter peripheral that manages
a number of 64-bit counters that are continuously updated as the simulator is
running. For each counter, it also provides a 64 bit "latching" register.

<p>The functionality of the counter peripheral is accessible through 3 registers:

<itemize>
<item><tt>PERIPHERALS_COUNTER_LATCH</tt> ($FFC0, write-only)
<item><tt>PERIPHERALS_COUNTER_SELECT</tt> ($FFC1, read/write)
<item><tt>PERIPHERALS_COUNTER_VALUE</tt> ($FFC2..$FFC9, read-only)
</itemize>

<p>These three registers are used as follows.

<p>When a program explicitly requests a "counter latch" operation by writing any value
to the <tt>PERIPHERALS_COUNTER_LATCH</tt> address ($FFC0), all live registers are simultaneously
copied to the latch registers. They will keep the newly latched value until another latch
operation is requested.

<p>The <tt>PERIPHERALS_COUNTER_SELECT</tt> address ($FFC1) register holds an 8-bit value that
specifies which 64-bit latch register is currently readable through the <tt>PERIPHERALS_COUNTER_VALUE</tt>
address range. Six values are currently defined:

<itemize>
<item>$00: latched clock cycle counter selected.
<item>$01: latched CPU instruction counter selected.
<item>$02: latched IRQ interrupt counter selected.
<item>$03: latched NMI interrupt counter selected.
<item>$80: latched wallclock time (nanoseconds) selected.
<item>$81: latched wallclock time (split s/ns) selected.
</itemize>

<p>Values $00 to $03 provide access to the latched (frozen) value of their respective live
counters at the time of the last write to <tt>PERIPHERALS_COUNTER_LATCH</tt>.

<p>When <tt>PERIPHERALS_COUNTER_LATCH</tt> equals $80, the <tt>PERIPHERALS_COUNTER_VALUE</tt>
will be a 64-bit value corresponding to the number of nanoseconds elapsed since Midnight, Jan 1st,
1970 UTC, at the time of the last latch operation.

<p>When <tt>PERIPHERALS_COUNTER_LATCH</tt> equals $81, the high 32 bits of <tt>PERIPHERALS_COUNTER_VALUE</tt>
will be a 32-bit value corresponding to the number of seconds elapsed since Midnight,
Jan 1st, 1970 UTC, at the time of the last latch operation. The low 32 bits of
<tt>PERIPHERALS_COUNTER_VALUE</tt> will hold the nanoseconds since the start of that second.

<p>The two different wallclock-time latch registers will always refer to precisely the same time instant.
For some applications, the single 64-bit value measured in nanoseconds will be more convenient, while
for other applications, the split 32/32 bits representations with separate second and nanosecond
values will be more convenient.

<p>Note that the definition above, with time elapsed measured since Midnight, Jan 1st, 1970 UTC, is
an approximation, as the implementation depends on the way POSIX definition time, and POSIX does
not account for leap seconds; it falsely assumes that all days are precisely 86400 seconds long.

<p>On reset, <tt>PERIPHERALS_COUNTER_SELECT</tt> is initialized to zero. If the <tt>PERIPHERALS_COUNTER_SELECT</tt>
register holds a value other than one of the six values described above, all <tt>PERIPHERALS_COUNTER_VALUE</tt>
bytes will read as zero.

<p>The <tt>PERIPHERALS_COUNTER_VALUE</tt> addresses ($FFC2..$FFC9) are used to read to currently
selected 64-bit latch register value. Address $FFC2 holds the least significant byte (LSB),
while address $FFC9 holds the most significant byte (MSB).

<p>On reset, all latch registers are reset to zero. Reading any of the <tt>PERIPHERALS_COUNTER_VALUE</tt>
bytes before the first write to <tt>PERIPHERALS_COUNTER_LATCH</tt> will yield zero.

Example:

<tscreen><verb>
#include <stdio.h>
#include <stdint.h>

volatile uint8_t  * CounterLatch  = (uint8_t *)0xffc0;
volatile uint8_t  * CounterSelect = (uint8_t *)0xffc1;
volatile uint32_t * CounterValue  = (uint32_t *)0xffc1;

static void print_current_counters(void)
{
    *CounterLatch = 0; /* latch values */

    *CounterSelect = 0x00;
    printf("clock cycles ............... : %08lx %08lx\n", CounterValue[1], CounterValue[0]);
    *CounterSelect = 0x01;
    printf("instructions ............... : %08lx %08lx\n", CounterValue[1], CounterValue[0]);
    *CounterSelect = 0x80;
    printf("wallclock time ............. : %08lx %08lx\n", CounterValue[1], CounterValue[0]);
    *CounterSelect = 0x81;
    printf("wallclock time, split ...... : %08lx %08lx\n", CounterValue[1], CounterValue[0]);
    printf("\n");
}

int main(void)
{
    print_current_counters();
    print_current_counters();
    return 0;
}
</verb></tscreen>

<sect>Copyright<p>

sim65 (and all cc65 binutils) are (C) Copyright 1998-2000 Ullrich von
Bassewitz. For usage of the binaries and/or sources the following conditions
do apply:

This software is provided 'as-is', without any expressed or implied
warranty.  In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

<enum>
<item>  The origin of this software must not be misrepresented; you must not
        claim that you wrote the original software. If you use this software
        in a product, an acknowledgment in the product documentation would be
        appreciated but is not required.
<item>  Altered source versions must be plainly marked as such, and must not
        be misrepresented as being the original software.
<item>  This notice may not be removed or altered from any source
        distribution.
</enum>

</article>