If detected, the program refuses to run, preventing a crash.
The check only works with SpartaDOS. I don't have an overview which
DOSes potentially use the RAM under the ROM. Or which other installed
programs might use it.
No additional runtime memory space is consumed, since the change
is in the "system check" load chunk which gets replaced by the
user program during loading.
Although documented nowhere (!!!) ProDOS trashes the random counter locations $4E/$4F. Is discovered this because my TCP connections didn't have random local ports.
It's a really funny coincidence that David Finnigan discovered only 3 years ago the very same issue because of the very same reason: https://groups.google.com/forum/#!topic/comp.sys.apple2.programmer/1ciep_Oetvo
In order to have randomize() work as expected (and the Apple II random number generation in general) it is necessary to update the random counter during keypress wait just like the ROM function does.
Extendend memory is mapped over the main memory in the 0x4000..0x7FFF
area. Many DOSes disable interrupts while extended memory is banked in,
but not all (e.g. SpartaDOS-X).
This change modifies the initial interrupt handler to map in main memory
before chaining to the "worker" handlers.
Since the initial interrupt handler uses a data segment to store the
trampoline to chain to the original handler, introduce a new "LOWBSS"
segment to hold this trampoline. Otherwise the trampoline may end up
inside the 0x4000..0x7FFF area.
Add a link time warning if "LOWCODE" segment lays within the extended
memory window.
Fixes this issue:
https://github.com/cc65/cc65/issues/722
ftell() returns the value returned by lseek(), and lseek() for the
Apple II wasn't returning a value.
According to https://github.com/cc65/wiki/wiki/Direct-console-IO it is undefined what happens when the end of the sceen is reached. But it is _not_ undefined what happens when the end of the line is reached. So implement the usual thing - which was easy enough to do after all.
Originally the Apple II had a 64 char set and used the upper two bits to control inverse and blinking. The Apple //e brought then an alternate char set without blinking but more individual chars. However, it does _not_ contain 128 chars and use the upper bit to control inverse as one would assume. Rather it contains more than 128 chars - the MouseText chars. And because Apple wanted to provide as much backward compatibility as possible with the original char set, the alternate char set has a rather weird layout for chars > 128 with the inverse lowercase chars _not_ at (normal lowercase char + 128).
So far the Apple II CONIO implementation mapped chars 128-255 to chars 0-127 (with the exception of \r and \n). It made use of alternate chars > 128 transparently for the user via reverse(1). The user didn't have direct access to the MouseText chars, they were only used interally for things like chline() and cvline().
Now the mapping of chars 128-255 to 0-127 is removed. Using chars > 128 gives the user direct access to the "raw" alternate chars > 128. This especially give the use direct access to the MouseText chars. But this clashes with the exsisting (and still desirable) revers(1) logic. Combining reverse(1) with chars > 128 just doesn't result in anything usable!
What motivated this change? When I worked on the VT100 line drawing support for Telnet65 on the Apple //e (not using CONIO at all) I finally understood how MouseText is intended to be used to draw arbitrary grids with just three chars: A special "L" type char, the underscore and a vertical bar at the left side of the char box. I notice that with those chars it is possible to follow the CONIO approach to boxes and grids: Combining chline()/cvline() with special CH_... char constants for edges and intersections.
But in order to actually do so I needed to be able to define CH_... constants that when fed into the ordinary cputc() pipeline end up as MouseText chars. The obvious approach was to allow chars > 128 to directly access MouseText chars :-)
Now that the native CONIO box/grid approach works I deleted the Apple //e proprietary textframe() function that I added as replacement quite some years ago.
Again: Please note that chline()/cvline() and the CH... constants don't work with reverse(1)!
We basically cast a struct timespec pointer to a time_t pointer when we pass the clock_settime() paramter to localtime(). Explicitly express that in the source code.
The CIA TOD only stores the time but not the date. Therefore the date set by clock_settime() ist just stored inside the C library for retrieval via clock_gettime().
The "very special" handling of 12AM/PM is based on https://groups.google.com/d/msg/comp.sys.cbm/ysVYSX4AMbc/vHrXCWEhCOUJ saying:
==========
24hr: Wr => Rd => Nx
--------------------
0 : 92 => 12 => 01 <= Switch from 00 to 01 (24-hour notation)
1 : 01 => 01 => 02
2 : 02 => 02 => 03
11 : 11 => 11 => 92
12 : 12 => 92 => 81 <= Switch from 12 to 13 (24-hour notation)
13 : 81 => 81 => 82
14 : 82 => 82 => 83
23 : 91 => 91 => 12
1. column ("24hr"): hour to be tested (decimal)
2. column ("Wr"): hour written to TOD register (BCD)
3. column ("Rd"): hour read from TOD register (BCD) immediately after writing the value in column 2 to see the conversion between AM/PM, if any
4. column ("Nx"): next hour (BCD) after the hour switch
==========
Thanks Paul!
The situation on the Apple II is rather special: There are several types of RTCs. It's not desirable to have specific code for all of them. As the OS supports file timestamps RTC owners usually use OS drivers for their RTC. Those drivers read the RTC and write the result in a "date/time location" in RAM. The OS reads the date/time from the RAM location. If there's no RTC the RAM location keeps containing zeros. The OS uses those zeros as timestamps and the files show up in a directory as "<NO DATE>".
There's no common interface to set RTCs so if an RTC _IS_ present there's just nothing to do. However, if there's _NO_ RTC present the user might very well be interest to "manually" set the RAM location in order to have timestamps. But he surely doesn't want to manually set the RAM location over an over again. Rather he wants to set it just once after booting the OS.
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 "DD-MON-YY 0:00".
So clock_settime() checks if the current time equals 0:00. If it does _NOT_ then an RTC is supposed to be active and clock_settime() fails with ERANGE. Otherwise clock_settime() ignores sets the date - and completely ignores the time provided as parameter.
clock_getres() too checks if the current time equals 0:00. If it does _NOT_ then an RTC is supposed to be active and clock_getres() returns a time resolution of one minute. Otherwise clock_getres() presumes that the only one who sets the RAM location is clock_settime() and therefore returns a time resolution of one day.
