build: Digilent backend on by default on UNIX

The driver dlopen's libdjtg/libdmgr and degrades to "no probe" if
they're absent, so building it in has no cost or dependency.
BS_ENABLE_DIGILENT now defaults ON on UNIX (needs <dlfcn.h>); disable
with -DBS_ENABLE_DIGILENT=OFF. Docs updated; also fixes the quartiq
license note in CLAUDE.md (MIT, not BSD-2).

CLAUDE.md

@@ -103,9 +103,12 @@ high ("all ones" symptom). Standard FTDI driver path is dead on these
 boards.
 
 Workaround: `modules/drivers/digilent_jtag/` wraps libdjtg/libdmgr
-(Digilent Adept Runtime). Built only when `-DBS_ENABLE_DIGILENT=ON`,
-loaded via `dlopen` at runtime — no Digilent binary or header in the
-repo. End-user just needs the Adept Runtime package installed.
+(Digilent Adept Runtime), loaded via `dlopen` at runtime — no Digilent
+binary or header in the repo. Because it's dlopen'd (degrades to "no
+probe" if the libs are absent), it costs nothing to build in:
+`BS_ENABLE_DIGILENT` defaults **ON** on UNIX (`<dlfcn.h>` required),
+disable with `-DBS_ENABLE_DIGILENT=OFF`. Adept Runtime is only needed
+at runtime to actually drive such a probe.
 
 ### Xilinx caveats
 
@@ -120,7 +123,7 @@ then `JSTART` and check `DONE`.
 
 ## External references
 
-- **BSCAN proxy bitstreams**: `quartiq/bscan_spi_bitstreams` (BSD-2).
+- **BSCAN proxy bitstreams**: `quartiq/bscan_spi_bitstreams` (MIT).
   Pre-built `.bit` for most Xilinx parts; Migen sources to rebuild any
   part that's missing (needs Vivado).
 - **Reference host-side implementation**: `openocd/src/flash/nor/jtagspi.c`.
@@ -138,9 +141,9 @@ mkdir build && cd build && cmake .. && make
 ./bs/bs           # interactive REPL
 ```
 
-For Digilent SMT2-based boards, configure with
-`cmake -DBS_ENABLE_DIGILENT=ON ..` and install the Adept Runtime
-system-wide (provides `libdjtg.so` + `libdmgr.so`).
+The Digilent SMT2 backend is built by default on UNIX (disable with
+`-DBS_ENABLE_DIGILENT=OFF`). To actually use such a probe, install the
+Adept Runtime system-wide (provides `libdjtg.so` + `libdmgr.so`).
 
 No automated tests yet. Smoke test = banner appears, `exit` works.
 After changes touching `jtag_core`, `drivers/ftdi_jtag`, or the

CMakeLists.txt

@@ -2,10 +2,17 @@ cmake_minimum_required(VERSION 3.10)
 
 project(BoundaryScanExplorer)
 
-# Optional backends. Off by default: no proprietary runtime dependency.
+# Digilent JTAG-SMT* backend. The driver dlopen's libdjtg/libdmgr at
+# runtime and degrades to "no probe" if they're absent, so building it
+# in costs nothing — default ON. Needs <dlfcn.h>, so UNIX only.
+if(UNIX)
+    set(BS_DIGILENT_DEFAULT ON)
+else()
+    set(BS_DIGILENT_DEFAULT OFF)
+endif()
 option(BS_ENABLE_DIGILENT
-       "Enable Digilent JTAG-SMT* backend (dlopen libdjtg.so / libdmgr.so at runtime; requires Adept Runtime installed)"
-       OFF)
+       "Enable Digilent JTAG-SMT* backend (dlopen libdjtg.so / libdmgr.so at runtime; Adept Runtime only needed to actually use such a probe)"
+       ${BS_DIGILENT_DEFAULT})
 
 # script and jtag_core must be the last linked archive for the application to compile
 set(BS_MODULES script jtag_core)

README.md

@@ -26,11 +26,12 @@ in `bsdl_files/`.
 - CMake ≥ 3.10, gcc/clang
 - `readline` (Arch: `readline`, Debian/Ubuntu: `libreadline-dev`)
 - `libftd2xx` for FTDI probes (vendored in `libs/libftd2xx/`)
-- *Optional, for Digilent SMT2/SMT2-NC boards:* the Digilent
+- *To drive a Digilent SMT2/SMT2-NC probe:* the Digilent
   [Adept Runtime](https://digilent.com/shop/software/digilent-adept/)
   installed system-wide (provides `libdjtg.so` + `libdmgr.so`).
   Nothing from Digilent is vendored — the backend is `dlopen`'d at
-  runtime.
+  runtime, so it's built in by default and simply reports no probe if
+  the libs are missing.
 
 ## Build
 
@@ -42,10 +43,10 @@ make
 
 The binary is produced at `build/bs/bs`.
 
-To enable the Digilent SMT2 backend:
+The Digilent SMT2 backend is built by default on Linux. To leave it out:
 
 ```sh
-cmake -DBS_ENABLE_DIGILENT=ON ..
+cmake -DBS_ENABLE_DIGILENT=OFF ..
 ```
 
 ## Run
@@ -114,11 +115,12 @@ Use `help <command>` for per-command help.
   in `modules/config/config.script` for pin mapping and TCK frequency.
 - **SEGGER J-Link**
 - **Linux GPIO** (sysfs; deprecated on recent kernels, libgpiod migration TBD)
-- **Digilent JTAG-SMT2 / SMT2-NC** — optional, built when
-  `-DBS_ENABLE_DIGILENT=ON`. Required for the USB-JTAG on Xilinx eval
-  boards like the KCU105: those modules ship a Digilent-proprietary
-  firmware that does not respond to plain MPSSE, so the FTDI driver
-  appears to enumerate them but the JTAG chain stays silent.
+- **Digilent JTAG-SMT2 / SMT2-NC** — built in by default on Linux
+  (`-DBS_ENABLE_DIGILENT=OFF` to drop it). Required for the USB-JTAG on
+  Xilinx eval boards like the KCU105: those modules ship a
+  Digilent-proprietary firmware that does not respond to plain MPSSE,
+  so the FTDI driver appears to enumerate them but the JTAG chain stays
+  silent.
 
 ## Known Xilinx caveats