Building for DOS
The DOS target is still a supported FreeBASIC target, but it is not shaped like
a modern hosted operating system. It normally uses a DJGPP-style toolchain and
has platform limits that the compiler and runtime must respect.
Current build path
Use the DOS build scripts when they are available in the checkout. They encode
the current toolchain layout and package expectations better than the old manual
DJGPP notes did.
For direct make work, prefer a target triplet rather than old short target
names:
Known DOS limits
Most normal compiler and runtime work is usable on DOS, but DOS-specific limits
remain important. The default DJGPP DOS runtime leaves threads and TCP
disabled. An explicit
DOS_TCP_PROVIDER=watt32 build can add IPv4 TCP through Watt-32 when a packet
driver and WATTCP.CFG are present, but it does not enable -mt.
FreeDOS programs built with DJGPP need a DPMI host such as CWSDPMI or HDPMI.
JEMM is an expanded memory manager/V86 monitor, not a DPMI host.
If the DPMI host has been tested with the target DOSBox or machine, add
DOS_DPMI_YIELD=YesPlease to make the DJGPP delay path issue the DPMI
release-time-slice request. A host that implements this request can run other
activities while a program is in SLEEP or DELAY. It does not create
parallel FreeBASIC threads, and the default remains disabled because some DOS
extenders do not safely implement the yield path. The existing
fb_dos_no_dpmi_yield variable can still force the conservative behavior at
run time.
The separate -target dos-hx workflow is an experimental route for testing
Win32 programs with HX's preemptive scheduler under DOS. It emits an ordinary x86
Win32 PE image for HX, so the existing Win32 CreateThread, wait, mutex,
condition-variable, and Winsock runtime paths remain in use. Run HX's
PatchPE tool on the image and ship the matching HX files. The HX route is a
Win32-under-DOS deployment profile, not an extension of the DJGPP DOS ABI.
The target alias does not establish that HX supports every imported API.
An optional native thread runtime is available with
DOS_THREAD_PROVIDER=pdmlwp. Compile and link programs using
-target dos -dos-threads pdmlwp. It provides RTC-preempted shared-memory
threads on one CPU, TLS, mutexes and condition variables. Threaded sfxlib
feeds Sound Blaster DMA from a worker and uses completion interrupts where
available. PC speaker output can use a worker-fed queue with an 8192 Hz RTC
consumer while thread scheduling stays at 128 Hz. Conflicting RTC use retains
synchronous speaker writes. Ordinary -mt alone is still rejected on DOS.
This profile requires x87 code and exclusive periodic RTC ownership; it does
not support SSE, ThreadCall or multicore execution. Foreign libraries still
need reentrancy review. The source tree's docs/freedos-providers.md records
the provider license, build instructions, limitations and DOSBox-X tests with
FreeDOS 1.4/CWSDPMI r7. The default DOS/QB profile remains separate.
The DOS target is still a supported FreeBASIC target, but it is not shaped like
a modern hosted operating system. It normally uses a DJGPP-style toolchain and
has platform limits that the compiler and runtime must respect.
Current build path
Use the DOS build scripts when they are available in the checkout. They encode
the current toolchain layout and package expectations better than the old manual
DJGPP notes did.
(sh) ./build_scripts/msdos-build-freebasic.sh ./build_scripts/msdos-test-freebasic.sh
For direct make work, prefer a target triplet rather than old short target
names:
(sh) make print-config TARGET_TRIPLET=i586-pc-msdosdjgpp make TARGET_TRIPLET=i586-pc-msdosdjgpp
Known DOS limits
Most normal compiler and runtime work is usable on DOS, but DOS-specific limits
remain important. The default DJGPP DOS runtime leaves threads and TCP
disabled. An explicit
DOS_TCP_PROVIDER=watt32 build can add IPv4 TCP through Watt-32 when a packet
driver and WATTCP.CFG are present, but it does not enable -mt.
FreeDOS programs built with DJGPP need a DPMI host such as CWSDPMI or HDPMI.
JEMM is an expanded memory manager/V86 monitor, not a DPMI host.
If the DPMI host has been tested with the target DOSBox or machine, add
DOS_DPMI_YIELD=YesPlease to make the DJGPP delay path issue the DPMI
release-time-slice request. A host that implements this request can run other
activities while a program is in SLEEP or DELAY. It does not create
parallel FreeBASIC threads, and the default remains disabled because some DOS
extenders do not safely implement the yield path. The existing
fb_dos_no_dpmi_yield variable can still force the conservative behavior at
run time.
The separate -target dos-hx workflow is an experimental route for testing
Win32 programs with HX's preemptive scheduler under DOS. It emits an ordinary x86
Win32 PE image for HX, so the existing Win32 CreateThread, wait, mutex,
condition-variable, and Winsock runtime paths remain in use. Run HX's
PatchPE tool on the image and ship the matching HX files. The HX route is a
Win32-under-DOS deployment profile, not an extension of the DJGPP DOS ABI.
The target alias does not establish that HX supports every imported API.
An optional native thread runtime is available with
DOS_THREAD_PROVIDER=pdmlwp. Compile and link programs using
-target dos -dos-threads pdmlwp. It provides RTC-preempted shared-memory
threads on one CPU, TLS, mutexes and condition variables. Threaded sfxlib
feeds Sound Blaster DMA from a worker and uses completion interrupts where
available. PC speaker output can use a worker-fed queue with an 8192 Hz RTC
consumer while thread scheduling stays at 128 Hz. Conflicting RTC use retains
synchronous speaker writes. Ordinary -mt alone is still rejected on DOS.
This profile requires x87 code and exclusive periodic RTC ownership; it does
not support SSE, ThreadCall or multicore execution. Foreign libraries still
need reentrancy review. The source tree's docs/freedos-providers.md records
the provider license, build instructions, limitations and DOSBox-X tests with
FreeDOS 1.4/CWSDPMI r7. The default DOS/QB profile remains separate.