The emulated serial port's modem status and control signals are not
tied to the signals on the real serial port, because the real signals
are not available to software through the Unix tty device interface.
The ability to check for parity, framing, and overrun errors and
receive an interrupt when one occurs is not emulated. Unix does not
support 2000, 3600, or 7200 baud, so these TRS-80 data rates are
remapped to 38400, 57600, and 115200 baud respectively.
Some features of the floppy disk controller are not currently emulated:
Force Interrupt with condition bits 0x01, 0x02, or 0x04 is not
implemented. Read Track is implemented only for DMK emulated floppies.
The multiple-sector flags in Read and Write are not implemented. The
timing of returned sectors is emulated only for the Read Address command,
and not very accurately for JV1 or JV3. If a disk has more than one
sector with the same number on a track, sdltrs will always see the first
(counting from the index hole) when reading or writing; a real machine
would see the next one to come under the head depending on the current
rotational position of the disk. Partially reformatting a track (which
TRS-80 programs like HyperZap and Model I Super Utility do to achieve
mixed density) is supported for DMK but not JV3; however, switching
densities while formatting (which Model III and 4 Super Utility do)
works on both DMK and JV3.
Real physical floppy disks are supported only under Linux, because the
other OS's does not define a portable interface to the low-level floppy
controller functionality that sdltrs needs, or support the floppy
controllers themselves. Also note, this is untested in sdltrs,
but was just brought over from xtrs. There are some limitations
even under Linux: Index holes are faked, not detected on the real disk,
and the timing of returned sectors is not emulated at all. Due to the
limitations of PC-style floppy disk controllers, when formatting a
physical floppy under sdltrs, you cannot mix sectors of different sizes
on the same track, switch densities in the middle of a track, or
reformat only part of a track. However, sdltrs can read and write to
physical floppies that have already been formatted in these ways
(perhaps by a real TRS-80).
The extended JV3 limit of 5802 sectors is somewhat arbitrary. It could
be raised by generalizing the code to permit more than two blocks of
2901, but this does not seem too useful. 5802 sectors is already
enough for a 3.5-inch HD (1.44MB) floppy, which the TRS-80 didn't
support anyway. If you need more space, use emulated hard drives instead
of emulated floppies with huge numbers of tracks.
XTRSHARD/DCT ignores the internal write-protected flag in hard drive
images, but a hard drive image can still be effectively write protected
by turning off its Unix write permission bits.
The emulator uses a heuristic to decide what format a ROM file is in.
If a raw binary ROM image starts with 0x01, 0x05, or 0x22, it can be
misidentified as being in a different format. This is rather unlikely
to occur, as ROMs typically begin with 0xF3, the DI instruction.
If you discover other bugs, write fixes for any of these, or make any
other enhancements, please let us know so that we can incorporate the
changes into future releases.
