cc65/doc/apple2.sgml

<!doctype linuxdoc system>

<article>
<title>Apple&nbsp;&rsqb;&lsqb; specific information for cc65
<author><url url="mailto:ol.sc@web.de" name="Oliver Schmidt">

<abstract>
An overview over the Apple&nbsp;&rsqb;&lsqb; runtime system as it is
implemented for the cc65 C compiler.
</abstract>

<!-- Table of contents -->
<toc>

<!-- Begin the document -->

<sect>Overview<p>

This file contains an overview of the Apple&nbsp;&rsqb;&lsqb; runtime system
as it comes with the cc65 C compiler. It describes the memory layout,
Apple&nbsp;&rsqb;&lsqb; specific header files, available drivers, and any
pitfalls specific to that platform.

Please note that Apple&nbsp;&rsqb;&lsqb; specific functions are just mentioned
here, they are described in detail in the separate <url url="funcref.html"
name="function reference">. Even functions marked as "platform dependent" may
be available on more than one platform. Please see the function reference for
more information.



<sect>Binary format<p>

The standard binary file format generated by the linker for the
Apple&nbsp;&rsqb;&lsqb; target is an <url name="AppleSingle"
url="http://kaiser-edv.de/documents/AppleSingle_AppleDouble.pdf"> file.
The default load address is &dollar;803.

<bf/AppleCommander 1.4.0/ or later (available at <url
url="https://applecommander.github.io/">) includes the option <tt/-as/ that
allows to put AppleSingle files onto disk images containing DOS 3.3 as well
as ProDOS 8.


<sect>Memory layout<p>

In the standard setup, cc65 generated programs use the memory from
&dollar;803 to &dollar;95FF, so 35.5 KB of RAM are available.

Special locations:

<descrip>

  <tag/Stack/
  The C runtime stack is located at HIMEM and grows downwards, regardless of
  how your linker config file is setup.

  <tag/Heap/
  The C heap is located at the end of the program and grows towards the C
  runtime stack.

</descrip><p>

While running <tt/main()/ the Language Card bank 2 is enabled for read access.
However while running module constructors/destructors the Language Card is disabled.

Enabling the Language Card allows to use it as additional memory for cc65
generated code. However code is never automatically placed there. Rather code
needs to be explicitly placed in the Language Card either per file by compiling
with <tt/--code-name LC/ or per function by enclosing in <tt/#pragma code-name
(push, "LC")/ and <tt/#pragma code-name (pop)/. In either case the cc65 runtime
system takes care of actually moving the code into the Language Card.

The amount of memory available in the Language Card for generated code depends
on the <ref id="link-configs" name="linker configuration"> parameters. There are
several usefull settings:

<descrip>

  <tag>LC address: &dollar;D400, LC size: &dollar;C00</tag>
  For plain vanilla ProDOS 8 which doesn't actually use the Language Card bank 2
  memory from &dollar;D400 to &dollar;DFFF. This is the default setting.

  <tag>LC address: &dollar;D000, LC size: &dollar;1000</tag>
  For ProDOS 8 together with the function <tt/rebootafterexit()/. If a program
  doesn't quit to the ProDOS 8 dispatcher but rather reboots the machine after
  exit then a plain vanilla ProDOS 8 doesn't make use of the Language Card bank
  2 at all.

  <tag>LC address: &dollar;D000, LC size: &dollar;3000</tag>
  For plain vanilla DOS 3.3 which doesn't make use of the Language Card at all.

</descrip><p>



<sect>Linker configurations<label id="link-configs"><p>

The ld65 linker comes with a default config file for the Apple&nbsp;&rsqb;&lsqb;,
which is used via <tt/-t apple2/.
The apple2 package comes with additional secondary linker config files, which
are used via <tt/-t apple2 -C &lt;configfile&gt;/.


<sect1>default config file (<tt/apple2.cfg/)<label id="apple-def-cfg"><p>

Default configuration for a binary program.

Parameters:

<descrip>

  <tag><tt/STARTADDRESS:/ Program start address</tag>
  Default: &dollar;803. Use <tt/-S &lt;addr&gt;/ to set a different start address.

  <tag><tt/__EXEHDR__:/ AppleSingle executable file header</tag>
  Default: Yes. Use <tt/-D __EXEHDR__=0/ to omit the AppleSingle header.

  <tag><tt/__STACKSIZE__:/ C runtime stack size</tag>
  Default: &dollar;800. Use <tt/-D __STACKSIZE__=&lt;size&gt;/ to set a different
  stack size.

  <tag><tt/__HIMEM__:/ Highest usable memory address presumed at link time</tag>
  Default: &dollar;9600. Use <tt/-D __HIMEM__=&lt;addr&gt;/ to set a different
  highest usable address.

  <tag><tt/__LCADDR__:/ Address of code in the Language Card</tag>
  Default: &dollar;D400. Use <tt/-D __LCADDR__=&lt;addr&gt;/ to set a different
  code address.

  <tag><tt/__LCSIZE__:/ Size of code in the Language Card</tag>
  Default: &dollar;C00. Use <tt/-D __LCSIZE__=&lt;size&gt;/ to set a different
  code size.

</descrip><p>


<sect1><tt/apple2-system.cfg/<label id="apple-sys-cfg"><p>

Configuration for a system program running on ProDOS 8 and using the memory from
&dollar;2000 to &dollar;BEFF.

Parameters:

<descrip>

  <tag><tt/__EXEHDR__:/ AppleSingle executable file header</tag>
  Default: Yes. Use <tt/-D __EXEHDR__=0/ to omit the AppleSingle header.

  <tag><tt/__STACKSIZE__:/ C runtime stack size</tag>
  Default: &dollar;800. Use <tt/-D __STACKSIZE__=&lt;size&gt;/ to set a different
  stack size.

  <tag><tt/__LCADDR__:/ Address of code in the Language Card</tag>
  Default: &dollar;D400. Use <tt/-D __LCADDR__=&lt;addr&gt;/ to set a different
  code address.

  <tag><tt/__LCSIZE__:/ Size of code in the Language Card</tag>
  Default: &dollar;C00. Use <tt/-D __LCSIZE__=&lt;size&gt;/ to set a different
  code size.

</descrip><p>


<sect1><tt/apple2-hgr.cfg/<p>

Configuration for a program including a hires page. See <tt>testcode/lib/apple/hgrtest.c</tt>
for an example of such a program.

Parameters:

<descrip>

  <tag><tt/STARTADDRESS:/ Program start address</tag>
  Default: &dollar;803. Use <tt/-S &lt;addr&gt;/ to set a different start address.

  <tag><tt/__EXEHDR__:/ AppleSingle executable file header</tag>
  Default: Yes. Use <tt/-D __EXEHDR__=0/ to omit the AppleSingle header.

  <tag><tt/__STACKSIZE__:/ C runtime stack size</tag>
  Default: &dollar;800. Use <tt/-D __STACKSIZE__=&lt;size&gt;/ to set a different
  stack size.

  <tag><tt/__HIMEM__:/ Highest usable memory address presumed at link time</tag>
  Default: &dollar;9600. Use <tt/-D __HIMEM__=&lt;addr&gt;/ to set a different
  highest usable address.

  <tag><tt/__LCADDR__:/ Address of code in the Language Card</tag>
  Default: &dollar;D400. Use <tt/-D __LCADDR__=&lt;addr&gt;/ to set a different
  code address.

  <tag><tt/__LCSIZE__:/ Size of code in the Language Card</tag>
  Default: &dollar;C00. Use <tt/-D __LCSIZE__=&lt;size&gt;/ to set a different
  code size.

</descrip><p>


<sect1><tt/apple2-overlay.cfg/<p>

Configuration for an overlay program with up to nine overlays. The overlay files
don't include the AppleSingle header. See <tt>samples/overlaydemo.c</tt> for more
information on overlays.

Parameters:

<descrip>

  <tag><tt/STARTADDRESS:/ Program start address</tag>
  Default: &dollar;803. Use <tt/-S &lt;addr&gt;/ to set a different start address.

  <tag><tt/__EXEHDR__:/ AppleSingle executable file header</tag>
  Default: Yes. Use <tt/-D __EXEHDR__=0/ to omit the AppleSingle header.

  <tag><tt/__STACKSIZE__:/ C runtime stack size</tag>
  Default: &dollar;800. Use <tt/-D __STACKSIZE__=&lt;size&gt;/ to set a different
  stack size.

  <tag><tt/__HIMEM__:/ Highest usable memory address presumed at link time</tag>
  Default: &dollar;9600. Use <tt/-D __HIMEM__=&lt;addr&gt;/ to set a different
  highest usable address.

  <tag><tt/__LCADDR__:/ Address of code in the Language Card</tag>
  Default: &dollar;D400. Use <tt/-D __LCADDR__=&lt;addr&gt;/ to set a different
  code address.

  <tag><tt/__LCSIZE__:/ Size of code in the Language Card</tag>
  Default: &dollar;C00. Use <tt/-D __LCSIZE__=&lt;size&gt;/ to set a different
  code size.

  <tag><tt/__OVERLAYSIZE__:/ Size of code in the overlays</tag>
  Default: &dollar;1000. Use <tt/-D __OVERLAYSIZE__=&lt;size&gt;/ to set a different
  code size.

</descrip><p>


<sect1><tt/apple2-asm.cfg/<p>

Configuration for an assembler program that doesn't need a special setup.

Parameters:

<descrip>

  <tag><tt/STARTADDRESS:/ Program start address</tag>
  Default: &dollar;803. Use <tt/-S &lt;addr&gt;/ to set a different start address.

  <tag><tt/__EXEHDR__:/ AppleSingle executable file header</tag>
  Default: No. Use <tt/-u __EXEHDR__ apple2.lib/ to add the AppleSingle header.

</descrip><p>



<sect>ProDOS 8 system programs<p>

ProDOS 8 system programs are always loaded to the start address &dollar;2000.
For cc65 programs this means that the 6 KB from &dollar;800 to &dollar;2000 are
by default unused. There are however several options to make use of that memory
range.


<sect1>LOADER.SYSTEM<p>

The easiest (and for really large programs in fact the only) way to have a cc65
program use the memory from &dollar;800 to &dollar;2000 is to link it as binary
(as opposed to system) program using the default linker configuration
<ref id="apple-def-cfg" name="apple2.cfg"> with <tt/__HIMEM__/ set to &dollar;BF00
and load it with the LOADER.SYSTEM utility. The program then works like a system
program (i.e. quits to the ProDOS dispatcher).

Using LOADER.SYSTEM is as simple as copying it to the ProDOS 8 directory of the
program to load under name &lt;program&gt;.SYSTEM as a system program. For
example the program <tt/MYPROG/ is loaded by <tt/MYPROG.SYSTEM/. The right
AppleCommander option to put LOADER.SYSTEM on a ProDOS 8 disk image is <tt/-p/.


<sect1>Heap<p>

If the cc65 program can be successfully linked as system program using the linker
configuration <ref id="apple-sys-cfg" name="apple2-system.cfg">, but
uses the heap either explicitly or implicitly (i.e. by loading a driver) then
the memory from &dollar;800 to &dollar;2000 can be added to the heap by calling
<tt/_heapadd ((void *) 0x0800, 0x1800);/ at the beginning of <tt/main()/.


<sect1>ProDOS 8 I/O buffers<p>

ProDOS 8 requires for every open file a page-aligned 1 KB I/O buffer. By default
these buffers are allocated by the cc65 runtime system on the heap using
<tt/posix_memalign()/. While this is generally the best solution it means quite
some overhead for (especially rather small) cc65 programs which do open files
but don't make use of the heap otherwise.

The apple2 package comes with the alternative ProDOS 8 I/O buffer allocation
module <tt/apple2-iobuf-0800.o/ which uses the memory between &dollar;800 and
the program start address for the 1 KB I/O buffers. For system programs (with
start address &dollar;2000) this results in up to 6 I/O buffers and thus up to 6
concurrently open files.

While using <tt/_heapadd()/ as described in the section above together with the
default I/O buffer allocation basically yields the same placement of I/O buffers
in memory the primary benefit of <tt/apple2-iobuf-0800.o/ is a reduction in code
size - and thus program file size - of more than 1400 bytes.

Using <tt/apple2-iobuf-0800.o/ is as simple as placing it on the linker command
line like this:

<tscreen><verb>
cl65 -t apple2 -C apple2-system.cfg myprog.c apple2-iobuf-0800.o
</verb></tscreen>



<sect>Platform specific header files<p>

Programs containing Apple&nbsp;&rsqb;&lsqb; specific code may use the
<tt/apple2.h/ header file.


<sect1>Apple&nbsp;&rsqb;&lsqb; specific functions<p>

The functions listed below are special for the Apple&nbsp;&rsqb;&lsqb;. See
the <url url="funcref.html" name="function reference"> for declaration and
usage.

<itemize>
<item>_auxtype
<item>_dos_type
<item>_filetype
<item>get_ostype
<item>rebootafterexit
<item>ser_apple2_slot
<item>tgi_apple2_mix
</itemize>


<sect1>Hardware access<p>

There's currently no support for direct hardware access. This does not mean
you cannot do it, it just means that there's no help.



<sect>Loadable drivers<p>

The names in the parentheses denote the symbols to be used for static linking of the drivers.


<sect1>Graphics drivers<p>

<descrip>

  <tag><tt/a2.lo.tgi (a2_lo_tgi)/</tag>
  This driver features a resolution of 40&times;48 with 16 colors.

  The function <tt/tgi_apple2_mix()/ allows to activate 4 lines of text. The
  function clears the corresponding area at the bottom of the screen.

  <tag><tt/a2.hi.tgi (a2_hi_tgi)/</tag>
  This driver features a resolution of 280&times;192 with 8 colors and two
  hires pages. Note that programs using this driver will have to be linked
  with <tt/-S $4000/ to reserve the first hires page or with <tt/-S $6000/
  to reserve both hires pages.

  The function <tt/tgi_apple2_mix()/ allows to activate 4 lines of text. The
  function doesn't clear the corresponding area at the bottom of the screen.

  In memory constrained situations the memory from &dollar;803 to &dollar;1FFF
  can be made available to a program by calling <tt/_heapadd ((void *) 0x0803, 0x17FD);/
  at the beginning of <tt/main()/. Doing so is beneficial even if the program
  doesn't use the the heap explicitly because loading the driver (and in fact
  already opening the driver file) uses the heap implicitly.

</descrip><p>


<sect1>Extended memory drivers<p>

<descrip>

  <tag><tt/a2.auxmem.emd (a2_auxmem_emd)/</tag>
  Gives access to 47.5 KB RAM (190 pages of 256 bytes each) on an Extended
  80-Column Text Card.

  Note that this driver doesn't check for the actual existence of the memory
  and that it doesn't check for ProDOS 8 RAM disk content!

</descrip><p>


<sect1>Joystick drivers<p>

<descrip>

  <tag><tt/a2.stdjoy.joy (a2_stdjoy_joy)/</tag>
  Supports up to two standard analog joysticks connected to the game port of
  the Apple&nbsp;&rsqb;&lsqb;.

</descrip><p>


<sect1>Mouse drivers<p>

<descrip>

  <tag><tt/a2.stdmou.mou (a2_stdmou_mou)/</tag>
  Driver for the AppleMouse&nbsp;II Card. Searches all Apple&nbsp;II slots
  for an AppleMouse&nbsp;II Card compatible firmware. The default bounding
  box is &lsqb;0..279,0..191&rsqb;.

  Programs using this driver will have to be linked with <tt/-S $4000/
  to reserve the first hires page if they are intended to run on an
  Apple&nbsp;&rsqb;&lsqb; (in contrast to an Apple&nbsp;//e) because the
  AppleMouse&nbsp;II Card firmware writes to the hires page when initializing
  on that machine.

  Note that the Apple&nbsp;&rsqb;&lsqb; default mouse callbacks support text
  mode only.

</descrip><p>


<sect1>RS232 device drivers<p>

<descrip>

  <tag><tt/a2.ssc.ser (a2_ssc_ser)/</tag>
  Driver for the Apple&nbsp;II Super Serial Card. Supports up to 19200 baud,
  hardware flow control (RTS/CTS) and interrupt driven receives. Note
  that because of the peculiarities of the 6551 chip transmits are not
  interrupt driven, and the transceiver blocks if the receiver asserts
  flow control because of a full buffer.

  The driver defaults to slot 2. Call <tt/ser_apple2_slot()/ prior to
  <tt/ser_open()/ in order to select a different slot. <tt/ser_apple2_slot()/
  succeeds for all Apple&nbsp;II slots, but <tt/ser_open()/ fails with
  <tt/SER_ERR_NO_DEVICE/ if there's no SSC firmware found in the selected slot.

</descrip><p>



<sect>Limitations<p>


<sect1>DOS 3.3<p>

Although the standard binaries generated by the linker for the Apple&nbsp;&rsqb;&lsqb;
generally run both on DOS 3.3 (with Applesoft BASIC) and on ProDOS 8 (with
BASIC.SYSTEM) there are some limitations for DOS 3.3:

<descrip>

  <tag>Disk file I/O</tag>
  There's no disk file I/O support. Any attempt to use it yields an error with
  <tt/errno/ set to <tt/ENOSYS/. This implicitly means that loadable drivers
  are in general not functional as they depend on disk file I/O. Therefore the statically
  linked drivers have to be used instead.

  <tag/Interrupts/
  There's no <tt/interruptor/ support. Any attempt to use it yields the message
  'FAILED TO ALLOC INTERRUPT' on program startup. This implicitly means that
  mouse and RS232 device drivers are not functional as they depend on interrupts.

</descrip><p>


<sect1>Direct console I/O<p>

The Apple&nbsp;&rsqb;&lsqb; has no color text mode. Therefore the functions
<tt/textcolor()/, <tt/bgcolor()/ and <tt/bordercolor()/ have no effect.


<sect1>Random number generator<p>

The random number seed is generated from the time the program waits for user input.
Therefore it is necessary to wait for at least one user keypress either via Standard
I/O or via Direct console I/O before initializing the pseudo random number generator.


<sect1>Realtime clock<p>

There are several types of realtime clocks. It's not desirable to have specific code
for all of them. As ProDOS 8 supports file timestamps, realtime clock owners usually
use ProDOS 8 drivers for their realtime clock. Those drivers read the realtime clock
and write the result to the date/time location in RAM (&dollar;BF90 to &dollar;BF93).
ProDOS 8 reads the date/time from that RAM location. If there's no realtime clock the
RAM location keeps containing zeros. ProDOS 8 uses those zeros as timestamps and the
files show up in a directory as <tt/&lt;NO DATE&gt;/.

There's no common interface to set realtime clocks so if a realtme clock <bf/IS/
present there's just nothing to do. However, if there's <bf/NO/ realtime clock present,
the user might very well be interested to "manually" set the RAM location in order to
have timestamps. But he surely doesn't want to manually set the RAM location over and
over again. Rather he wants to set it just once after booting ProDOS 8.

From that perspective it makes most sense to not set both the date and the time but
rather only set the date and have the time just stay zero. Then files show up in a
directory as <tt/DD-MON-YY  0:00/.

So <tt/clock_settime()/ checks if the current time equals 0:00. If it does <bf/NOT/
then a realtime clock is supposed to be active and <tt/clock_settime()/ fails with
<tt/ERANGE/. Otherwise <tt/clock_settime()/ sets the date - and completely ignores
the time provided as parameter.

<tt/clock_getres()/ too checks if the current time equals 0:00. If it does <bf/NOT/
then a realtime clock is supposed to be active and <tt/clock_getres()/ returns a time
resolution of one minute. Otherwise <tt/clock_getres()/ presumes that the only one
who sets the RAM location is <tt/clock_settime()/ and therefore returns a time
resolution of one day.



<sect>Other hints<p>


<sect1>Passing arguments to the program<p>

Command line arguments can be passed to <tt/main()/ after BLOAD. Since this is not
supported by BASIC, the following syntax was chosen:

<tscreen><verb>
]CALL2051:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5
</verb></tscreen>

<enum>
<item>Arguments are separated by spaces.
<item>Arguments may be quoted.
<item>Leading and trailing spaces around an argument are ignored. Spaces within
      a quoted argument are allowed.
<item>The first argument passed to <tt/main/ is the program name.
<item>A maximum number of 10 arguments (including the program name) are
      supported.
</enum>


<sect1>Interrupts<p>

The runtime for the Apple&nbsp;&rsqb;&lsqb; uses routines marked as
<tt/.INTERRUPTOR/ for ProDOS 8 interrupt handlers. Such routines must be
written as simple machine language subroutines and will be called
automatically by the interrupt handler code when they are linked into a
program. See the discussion of the <tt/.CONDES/ feature in the <url
url="ca65.html" name="assembler manual">.


<sect1>DIO<p>

<descrip>

  <tag/Drive ID/
  The function <url url="dio.html#s1" name="dio_open()"> has the single
  parameter <tt/device/ to identify the device to be opened. Therefore an
  Apple&nbsp;II slot and drive pair is mapped to that <tt/device/ according
  to the formula

  <tscreen>
    device = slot + (drive - 1) * 8
  </tscreen>

  so that for example slot 6 drive 2 is mapped to <tt/device/ 14.

  <tag/Sector count/
  The function <url url="dio.html#s3" name="dio_query_sectcount()"> returns
  the correct sector count for all ProDOS 8 disks. However for any non-ProDOS 8
  disk it simply always returns 280 (which is only correct for a 140 KB disk).
  This condition is indicated by the <tt/_oserror/ value 82.

</descrip><p>


<sect1>Specifying file types for fopen<p>

<descrip>

  <tag>Explanation of File Types</tag>

  ProDOS associates a file type and an auxiliary type with each file.
  These type specifications are separate from the file's name, unlike
  Windows which uses the file name's suffix (a.k.a.
  extension) to specify the file type. For example, <tt/.exe/,
  <tt/.doc/, or <tt/.bat/.
  The ProDOS low-level
  Machine-Language Interface (MLI) functions for creating and opening
  files require these types to be specified. And if they don't match
  with the file being opened, the operation may fail.

  In contrast, the ISO C function <tt/fopen()/ and the POSIX function
  <tt/open()/ have no parameter to specify either a file type or an
  auxiliary type. Therefore, some additional mechanism for specifying
  the file types is needed.

  <tag>Specifying the File Type and Auxiliary Type</tag>

  There are two global variables provided that allow the file type
  and auxiliary type to be specified before a call to <tt/fopen()/
  or <tt/open()/. They are defined in <tt/apple2_filetype.h/:

  <tscreen>
  <verb>
  extern unsigned char _filetype;  /* Default: PRODOS_T_BIN */
  extern unsigned int _auxtype;    /* Default: 0            */
  </verb>
  </tscreen>

  The header file <tt/apple2_filetype.h/ also defines many values
  that can be used to set these variables. It is included in
  <tt/apple2.h/, which is in turn included in <tt/apple2enh.h/.
  So it isn't necessary to include it directly. Just
  include one of <tt/apple2.h/ or <tt/apple2enh.h/.

  <tag>Example</tag>

  A text file cannot be created with just the
  standard C functions because they default to the binary type
  <tt/PRODOS_T_BIN/. The <tt/_filetype/ variable must be set to
  <tt/PRODOS_T_TXT/ to create a text file.

  For a text file,
  <tt/_auxtype/ specifies the record length. A zero record
  length text file is referred to as a sequential text file.
  This is equivalent to text files on
  other operating systems, except that the line terminator is a
  carriage return instead of a line-feed (Linux/BSD/MacOS) or
  carriage return, line-feed pair (Windows).

  The "sequential" text file terminology is in contrast to a
  "random-access" text file which would
  have a fixed-length, non-zero record length, so that the
  file position of any individual record can be calculated.

  For this example, the
  <tt/_auxtype/ does not need to be set because it defaults to
  the desired value, which is zero. To be more explicit,
  <tt/_auxtype/ can also be set to <tt/PRODOS_AUX_T_TXT_SEQ/
  which is defined as zero.

  <tscreen>
  <verb>
    &num;include &lt;stdio.h&gt;
    &num;include &lt;string.h&gt;
    &num;include &lt;errno.h&gt;
    &num;include &lt;apple2.h&gt;

    void main(void)
    {
        FILE *out;
        char *name = "MY.FAVS";

        /*-----------------------------*/

        _filetype = PRODOS_T_TXT;
        _auxtype  = PRODOS_AUX_T_TXT_SEQ;

        /*-----------------------------*/

        if ((out = fopen(name, "w")) != NULL) {
            fputs("Jorah Mormont\r", out);
            fputs("Brienne of Tarth\r", out);
            fputs("Daenerys Targaryen\r", out);
            fputs("Sandor Clegane\r", out);
            if (fclose(out) == EOF) {
                fprintf(stderr, "fclose failed for %s: %s", name, strerror(errno));
            }
        }
        else {
            fprintf(stderr, "fopen failed for %s: %s", name, strerror(errno));
        }
    }
  </verb>
  </tscreen>

</descrip><p>


<sect>License<p>

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>