--------------------------------------------------------------------------------
Problem statement:

I tried to use SoapyAudio with Hamlib support enabled to control the
SoftRock Si570 AVR-USB radio.  I found that SoapyAudio forced me to
provide a serial rate even though USB devices don't have a settable
serial rate.  It seems SoapyAudio was coded presuming all devices are
controlled via serial ports, which may not be the case these days.

I found hamlib works when serial rate is set to zero for this radio. See
below for example of my trial and error efforts.  I found I had to make
small changes to SoapyAudio for its hamlib calls to work with a serial
rate of zero.  See below for code diffs.  

I am hopeful these changes enable all USB-controlled audio 'soundcard'
radios to work.  I improved the error message to help debug things when
they do not work.

Debug environment was Ubuntu 20.04, Hamlib 3.3, gqrx top of tree
(v2.14.1-7-ga98411f-dirty), SoapySDR info is shown below.  I did 
not test on anything but this environment with this radio. The scope
of the changes is limited to the hamlib portions of SoapyAudio so
they should not impact anything else.

--------------------------------------------------------------------------------
Initial build of SoapyAudio: Note use of 'cmake -DUSE_HAMLIB=ON ..'

user@host:~/code/sdr$ git clone https://github.com/pothosware/SoapyAudio
Cloning into 'SoapyAudio'...
remote: Enumerating objects: 165, done.
remote: Total 165 (delta 0), reused 0 (delta 0), pack-reused 165
Receiving objects: 100% (165/165), 194.88 KiB | 2.35 MiB/s, done.
Resolving deltas: 100% (80/80), done.
user@host:~/code/sdr$ cd SoapyAudio
user@host:~/code/sdr/SoapyAudio$ mkdir build; cd build
user@host:~/code/sdr/SoapyAudio/build$ cmake -DUSE_HAMLIB=ON ..
-- The CXX compiler identification is GNU 9.3.0
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Build type not specified: defaulting to release.
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29.1") 
-- Checking for module 'hamlib'
--   Found hamlib, version 3.3
-- Found hamlib 
-- Found hamlib: /usr/include  
-- Performing Test HAS_STD_CXX11
-- Performing Test HAS_STD_CXX11 - Success
-- Checking for module 'rtaudio'
--   Found rtaudio, version 5.0.0
-- Found RtAudio: /usr/lib/x86_64-linux-gnu/librtaudio.so (found version "5.0.0") 
-- Found Git: /usr/bin/git (found version "2.25.1") 
-- Module audioSupport configured with version: 0.1.1-2ae84e3
-- Configuring done
-- Generating done
-- Build files have been written to: ~/code/sdr/SoapyAudio/build
user@host:~/code/sdr/SoapyAudio/build$ (make && sudo make install && sudo ldconfig) |& tee make.log

--------------------------------------------------------------------------------
Finding SoapyAudio's device strings:

Reference: SoapyAudio/Settings.cpp

#ifdef USE_HAMLIB
    t_Rig = nullptr;
    rigThread = nullptr;
    rigModel = 0;
    rigFile = "";
    rigSerialRate = 0;
    
    if (args.count("rig") != 0 && args.at("rig") != "") {
        try {
            rigModel = std::stoi(args.at("rig"));
        } catch (const std::invalid_argument &) {
            throw std::runtime_error("rig is invalid.");
        }
        if (!args.count("rig_rate")) {
            throw std::runtime_error("rig_rate missing.");
        }
        try {
            rigSerialRate = std::stoi(args.at("rig_rate"));
        } catch (const std::invalid_argument &) {
            throw std::runtime_error("rig_rate is invalid.");
        }

        if (!args.count("rig_port")) {
            throw std::runtime_error("rig_port missing.");
        }
        rigFile = args.at("rig_port");
        checkRigThread();
    }
#endif

This shows that:
  - "rig" must be present and must be an integer
  - "rig_rate" must be present and must be an integer
  - "rig_port" must be present and is a file name

--------------------------------------------------------------------------------
Finding hamlib settings using rigctl

1) Find rig type

user@host:~/soapy-debug$ rigctl --l | grep Soft
  2509  SoftRock               Si570 AVR-USB           0.3             Beta

So Softrock is 2509.  Note all the 25xx radios use similar designs.

2) Find the radio's defaults: only one that is relevant is 'rig_pathname'

user@host:~/soapy-debug$ rigctl -m 2509 -L
...
rig_pathname: "Path name to the device file of the rig"
	Default: /dev/rig, Value: 
	String.
...
<CTRL-D>

At this point, try the following to get the rig to open.

Configure 'gqrx' to use the following device string (all one line):

device="default_input=True,default_output=False,device_id=0,
driver=audio,soapy=0,rig=2509,rig_rate=9600,rig_port=/dev/ttyS0

gives (in red):

[ERROR] Rig failed to init.

3) Try to get frequency using rig 2509, rig_port /dev/rig, rig_rate 9600 baud

user@host:~/soapy-debug$ rigctl -m 2509 -r /dev/rig -s 9600 f
rig_open: error = IO error 

4) Try lots of different common rig serial rates, the only one that works is 0

user@host:~/soapy-debug$ rigctl -m 2509 -r /dev/rig -s 0 f
7050099

5) Now we can set the frequency to 10.0 MHz and read it back

user@host:~/soapy-debug$ rigctl -m 2509 -r /dev/rig -s 0 F 10000000
user@host:~/soapy-debug$ rigctl -m 2509 -r /dev/rig -s 0 f
10000000

6) Start gqxr with device strings as below:

device="default_input=True,default_output=False,device_id=0,
driver=audio,soapy=0,rig=2509,rig_rate=0,rig_port=/dev/rig

7) Now gqrx starts and we receive WWV at 10.0 MHz even though the frequency 
displayed is wrong. Also, changing frequency does nothing, and we also see:

[ERROR] Rig failed to init.

8) Change code to support rig_rate=0 because rigctl shows that serial rate 0
is what works for USB controlled radios, diff below

--------------------------------------------------------------------------------
Code changes:

Notes:
  - Allow rig_rate (serialRate) to be 0 since this works for Softrock as
    shown via the rigctl command
  - When serialRate is 0 don't update the serial rate data structure, this
    seems to be union and writing it for USB radios causes the open call
    to fail 
  - Enhance the error handling for hamlib open and init calls
  - When rig open fails, show the settings made it into SoapyAudio along with 
    the hamlib error string
  - Eliminate unused 'status' variable so warnings go away

diff --git a/RigThread.cpp b/RigThread.cpp
index ac96cc2..cd3c03c 100644
--- a/RigThread.cpp
+++ b/RigThread.cpp
@@ -33,17 +33,28 @@ void RigThread::setup(rig_model_t rig_model, std::string rig_file, int serial_ra
 };
 
 void RigThread::run() {
-    int retcode, status;
+    int retcode;
 
     SoapySDR_log(SOAPY_SDR_DEBUG, "Rig thread starting.");    
 
     rig = rig_init(rigModel);
+    if (rig == NULL) {
+        SoapySDR_log(SOAPY_SDR_ERROR, "Rig failed to init.");
+        terminated.store(true);
+        return;
+    }
+
 	strncpy(rig->state.rigport.pathname, rigFile.c_str(), FILPATHLEN - 1);
-	rig->state.rigport.parm.serial.rate = serialRate;
+    if (serialRate > 0)  // bypass for rate 0 used for USB controlled radios
+	    rig->state.rigport.parm.serial.rate = serialRate;
+
 	retcode = rig_open(rig);
-    
     if (retcode != 0) {
-        SoapySDR_log(SOAPY_SDR_ERROR, "Rig failed to init.");
+        char s[BUFSIZ];
+        snprintf(s, BUFSIZ, "Rig failed to open, rig: %d rig_rate: %d "
+            "rig_port: %s error: %s.", 
+            rigModel, serialRate, rigFile.c_str(), rigerror(retcode));
+        SoapySDR_log(SOAPY_SDR_ERROR, s);
         terminated.store(true);
         return;
     }
@@ -57,7 +68,7 @@ void RigThread::run() {
     while (!terminated.load()) {
         std::this_thread::sleep_for(std::chrono::milliseconds(150));
         if (freqChanged.load()) {
-            status = rig_get_freq(rig, RIG_VFO_CURR, &freq);
+            rig_get_freq(rig, RIG_VFO_CURR, &freq);
             if (freq != newFreq) {
                 freq = newFreq;
                 rig_set_freq(rig, RIG_VFO_CURR, freq);
@@ -66,7 +77,7 @@ void RigThread::run() {
             
             freqChanged.store(false);
         } else {
-            status = rig_get_freq(rig, RIG_VFO_CURR, &freq);
+            rig_get_freq(rig, RIG_VFO_CURR, &freq);
         }
         
         SoapySDR_logf(SOAPY_SDR_DEBUG, "Rig Freq: %f", freq);
@@ -98,4 +109,4 @@ void RigThread::terminate() {
 bool RigThread::isTerminated() {
     return terminated.load();
 }
-#endif
\ No newline at end of file
+#endif
diff --git a/Settings.cpp b/Settings.cpp
index 172e5e4..10e0074 100644
--- a/Settings.cpp
+++ b/Settings.cpp
@@ -584,7 +584,7 @@ chanSetup SoapyAudio::chanSetupStrToEnum(std::string chanOpt) {
 
 #ifdef USE_HAMLIB
 void SoapyAudio::checkRigThread() {    
-    if (!rigModel || !rigSerialRate || rigFile == "") {
+    if (!rigModel || (rigSerialRate < 0) || rigFile == "") {
         return;
     }
     if (!rigThread) {
@@ -600,4 +600,4 @@ void SoapyAudio::checkRigThread() {
     }
 }
 
-#endif
\ No newline at end of file
+#endif

--------------------------------------------------------------------------------
SoapySDR Info

user@host:~/soapy-debug$ SoapySDRUtil --info
######################################################
##     Soapy SDR -- the SDR abstraction library     ##
######################################################

Lib Version: v0.8.0-g926c86d9
API Version: v0.8.0
ABI Version: v0.8
Install root: /usr/local
Search path:  /usr/local/lib/SoapySDR/modules0.8
Module found: /usr/local/lib/SoapySDR/modules0.8/libHackRFSupport.so   (0.3.3-7d53087)
Module found: /usr/local/lib/SoapySDR/modules0.8/libairspyhfSupport.so (0.1.1-b6cfbf5)
Module found: /usr/local/lib/SoapySDR/modules0.8/libaudioSupport.so    (0.1.1-2ae84e3)
Module found: /usr/local/lib/SoapySDR/modules0.8/libremoteSupport.so   (0.6.0-c09b2f1)
Module found: /usr/local/lib/SoapySDR/modules0.8/librtlsdrSupport.so   (0.3.1-52cb5c0)
Available factories... airspyhf, audio, hackrf, remote, rtlsdr
Available converters...
 -  CF32 -> [CF32, CS16, CS8, CU16, CU8]
 -  CS16 -> [CF32, CS16, CS8, CU16, CU8]
 -  CS32 -> [CS32]
 -   CS8 -> [CF32, CS16, CS8, CU16, CU8]
 -  CU16 -> [CF32, CS16, CS8]
 -   CU8 -> [CF32, CS16, CS8]
 -   F32 -> [F32, S16, S8, U16, U8]
 -   S16 -> [F32, S16, S8, U16, U8]
 -   S32 -> [S32]
 -    S8 -> [F32, S16, S8, U16, U8]
 -   U16 -> [F32, S16, S8]
 -    U8 -> [F32, S16, S8]

SoapyAudio/Registration.cpp:92:25: error: invalid conversion from ‘int (*)(const rig_caps*, void*)’ to ‘int (*)(rig_caps*, void*)’ [-fpermissive]
   92 |         rig_list_foreach(SoapyAudio::add_hamlib_rig, 0);
      |         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                         |
      |                         int (*)(const rig_caps*, void*)

$ git diff | cat
diff --git a/Registration.cpp b/Registration.cpp
index 82a3452..dae1891 100644
--- a/Registration.cpp
+++ b/Registration.cpp
@@ -97,7 +97,7 @@ static std::vector<SoapySDR::Kwargs> findAudio(const SoapySDR::Kwargs &args)
 }
 
 #ifdef USE_HAMLIB
-int SoapyAudio::add_hamlib_rig(const struct rig_caps *rc, void* f)
+int SoapyAudio::add_hamlib_rig(struct rig_caps *rc, void* f)
 {
     rigCaps.push_back(rc);
 	return 1;
diff --git a/SoapyAudio.hpp b/SoapyAudio.hpp
index 6eefb76..1a68589 100644
--- a/SoapyAudio.hpp
+++ b/SoapyAudio.hpp
@@ -259,7 +259,7 @@ public:
 
 #ifdef USE_HAMLIB
 public:
-    static int add_hamlib_rig(const struct rig_caps *rc, void* f);
+    static int add_hamlib_rig(struct rig_caps *rc, void* f);
     static std::vector<const struct rig_caps *> rigCaps;
     
     void checkRigThread();

-- The CXX compiler identification is GNU 13.2.1
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Performing Test HAS_STD_CXX11
-- Performing Test HAS_STD_CXX11 - Success
-- Found PkgConfig: /usr/bin/pkg-config (found version "1.8.1")
-- Checking for module 'rtaudio'
--   Found rtaudio, version 6.0.1
-- Found RtAudio: /usr/lib/librtaudio.so (found version "6.0.1")
-- Module audioSupport configured with version: 0.1.1
-- Configuring done (0.7s)
-- Generating done (0.0s)
-- Build files have been written to: /build/soapyaudio/src/build
Change Dir: '/build/soapyaudio/src/build'

Run Build Command(s): /usr/bin/cmake -E env VERBOSE=1 /usr/bin/make -f Makefile
/usr/bin/cmake -S/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1 -B/build/soapyaudio/src/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /build/soapyaudio/src/build/CMakeFiles /build/soapyaudio/src/build//CMakeFiles/progress.marks
/usr/bin/make  -f CMakeFiles/Makefile2 all
make[1]: Entering directory '/build/soapyaudio/src/build'
/usr/bin/make  -f CMakeFiles/audioSupport.dir/build.make CMakeFiles/audioSupport.dir/depend
make[2]: Entering directory '/build/soapyaudio/src/build'
cd /build/soapyaudio/src/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1 /build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1 /build/soapyaudio/src/build /build/soapyaudio/src/build /build/soapyaudio/src/build/CMakeFiles/audioSupport.dir/DependInfo.cmake "--co
lor="
make[2]: Leaving directory '/build/soapyaudio/src/build'
/usr/bin/make  -f CMakeFiles/audioSupport.dir/build.make CMakeFiles/audioSupport.dir/build
make[2]: Entering directory '/build/soapyaudio/src/build'
[ 40%] Building CXX object CMakeFiles/audioSupport.dir/Registration.cpp.o
[ 40%] Building CXX object CMakeFiles/audioSupport.dir/Version.cpp.o
[ 80%] Building CXX object CMakeFiles/audioSupport.dir/Streaming.cpp.o
[ 80%] Building CXX object CMakeFiles/audioSupport.dir/Settings.cpp.o
/usr/bin/c++ -D_REENTRANT -DaudioSupport_EXPORTS -I/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1 -I/usr/include/rtaudio -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions         -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security         -fstack-clash-protection -fcf-protection -Wp,-D_GLIBCXX_ASSE
RTIONS -g -ffile-prefix-map=/build/soapyaudio/src=/usr/src/debug/soapyaudio -flto=auto -std=c++11 -fPIC -fvisibility=hidden -fvisibility-inlines-hidden   -Wno-unused-parameter -Wall -Wextra -Wnon-virtual-dtor -MD -MT CMakeFiles/audioSupport.dir/Registration.cpp.o -MF CMakeFiles/audioSupport.dir/Registration.cpp.o.d -o
 CMakeFiles/audioSupport.dir/Registration.cpp.o -c /build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Registration.cpp
/usr/bin/c++ -D_REENTRANT -DaudioSupport_EXPORTS -I/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1 -I/usr/include/rtaudio -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions         -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security         -fstack-clash-protection -fcf-protection -Wp,-D_GLIBCXX_ASSE
RTIONS -g -ffile-prefix-map=/build/soapyaudio/src=/usr/src/debug/soapyaudio -flto=auto -std=c++11 -fPIC -fvisibility=hidden -fvisibility-inlines-hidden   -Wno-unused-parameter -Wall -Wextra -Wnon-virtual-dtor -MD -MT CMakeFiles/audioSupport.dir/Version.cpp.o -MF CMakeFiles/audioSupport.dir/Version.cpp.o.d -o CMakeFile
s/audioSupport.dir/Version.cpp.o -c /build/soapyaudio/src/build/Version.cpp
/usr/bin/c++ -D_REENTRANT -DaudioSupport_EXPORTS -I/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1 -I/usr/include/rtaudio -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions         -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security         -fstack-clash-protection -fcf-protection -Wp,-D_GLIBCXX_ASSE
RTIONS -g -ffile-prefix-map=/build/soapyaudio/src=/usr/src/debug/soapyaudio -flto=auto -std=c++11 -fPIC -fvisibility=hidden -fvisibility-inlines-hidden   -Wno-unused-parameter -Wall -Wextra -Wnon-virtual-dtor -MD -MT CMakeFiles/audioSupport.dir/Settings.cpp.o -MF CMakeFiles/audioSupport.dir/Settings.cpp.o.d -o CMakeFi
les/audioSupport.dir/Settings.cpp.o -c /build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Settings.cpp
/usr/bin/c++ -D_REENTRANT -DaudioSupport_EXPORTS -I/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1 -I/usr/include/rtaudio -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions         -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security         -fstack-clash-protection -fcf-protection -Wp,-D_GLIBCXX_ASSE
RTIONS -g -ffile-prefix-map=/build/soapyaudio/src=/usr/src/debug/soapyaudio -flto=auto -std=c++11 -fPIC -fvisibility=hidden -fvisibility-inlines-hidden   -Wno-unused-parameter -Wall -Wextra -Wnon-virtual-dtor -MD -MT CMakeFiles/audioSupport.dir/Streaming.cpp.o -MF CMakeFiles/audioSupport.dir/Streaming.cpp.o.d -o CMake
Files/audioSupport.dir/Streaming.cpp.o -c /build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Streaming.cpp
/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Streaming.cpp: In member function ‘virtual int SoapyAudio::activateStream(SoapySDR::Stream*, int, long long int, size_t)’:
/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Streaming.cpp:242:14: error: ‘RtAudioError’ does not name a type; did you mean ‘RtAudioErrorType’?
  242 |     } catch (RtAudioError& e) {
      |              ^~~~~~~~~~~~
      |              RtAudioErrorType
/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Streaming.cpp:243:59: error: ‘e’ was not declared in this scope
  243 |         throw std::runtime_error("RtAudio init error '" + e.getMessage());
      |                                                           ^
/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Settings.cpp: In member function ‘virtual void SoapyAudio::writeSetting(const std::string&, const std::string&)’:
/build/soapyaudio/src/SoapyAudio-soapy-audio-0.1.1/Settings.cpp:497:40: warning: catching polymorphic type ‘class std::invalid_argument’ by value [-Wcatch-value=]
  497 |         } catch (std::invalid_argument e) { }
      |                                        ^
make[2]: *** [CMakeFiles/audioSupport.dir/build.make:104: CMakeFiles/audioSupport.dir/Streaming.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[2]: Leaving directory '/build/soapyaudio/src/build'
make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/audioSupport.dir/all] Error 2
make[1]: Leaving directory '/build/soapyaudio/src/build'
make: *** [Makefile:136: all] Error 2

ncorgan@edi:~/dev/sdr/build/SoapyAudio$ SoapySDRUtil --find=driver=audio
######################################################
##     Soapy SDR -- the SDR abstraction library     ##
######################################################


RtApiAlsa::getDeviceInfo: snd_pcm_open error for device (hw:0,0), Device or resource busy.

Found device 0
  default_input = True
  default_output = False
  device_id = 0
  driver = audio
  label = hw:HDA Intel PCH,0

Found device 1
  default_input = False
  default_output = False
  device_id = 2
  driver = audio
  label = default

ncorgan@edi:~/dev/sdr/build/SoapyAudio$ uhd_find_devices 
[INFO] [UHD] linux; GNU C++ version 7.4.0; Boost_106501; UHD_3.14.1.HEAD-0-gbfb9c1c7

RtApiAlsa::getDeviceInfo: snd_pcm_open error for device (hw:0,0), Device or resource busy.

--------------------------------------------------
-- UHD Device 0
--------------------------------------------------
Device Address:
    serial: 
    default_input: False
    default_input: True
    default_output: False
    device_id: 0
    device_id: 2
    driver: audio
    label: default
    label: hw:HDA Intel PCH,0
    type: soapy