From 5e29e7eeb0ade2b07ca0c702b823b266dfbf705a Mon Sep 17 00:00:00 2001
From: Henner Zeller <h.zeller@acm.org>
Date: Fri, 14 Oct 2016 19:00:57 -0700
Subject: [PATCH] o Output a warning if the sound modules is detected.

---
 README.md   | 13 ++++++++-----
 lib/gpio.cc | 22 ++++++++++++++++++++++
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index a2a0b58..e66ac22 100644
--- a/README.md
+++ b/README.md
@@ -297,11 +297,14 @@ Troubleshooting
 Here are some tips in case things don't work as expected.
 
 ### Use minimal Raspbian distribution
-In general, run a minimal configuration on your Pi. There were some
-unconfirmed reports of problems with Pis running GUI systems. Even though the
-Raspberry Pi foundation makes you believe that you can do that: don't. Using it
-with a GUI is a frustratingly slow use of an otherwise perfectly good
-embedded device.
+In general, run a minimal configuration on your Pi.
+
+  * Do not use a graphical user interface (Even though the
+    Raspberry Pi foundation makes you believe that you can do that: don't.
+    Using a Pi with a GUI is a frustratingly slow use of an otherwise
+    perfectly good embedded device.)
+
+  * Switch off on-board sound (external USB sound adapters work).
 
 Everything seems to work well with a **[Raspbian Lite][raspbian-lite]**
 distribution.
diff --git a/lib/gpio.cc b/lib/gpio.cc
index 9c0c0cb..3f11542 100644
--- a/lib/gpio.cc
+++ b/lib/gpio.cc
@@ -214,6 +214,22 @@ private:
   const std::vector<int> nano_specs_;
 };
 
+static bool LinuxHasModuleLoaded(const char *name) {
+  FILE *f = fopen("/proc/modules", "r");
+  if (f == NULL) return false; // don't care.
+  char buf[256];
+  const size_t namelen = strlen(name);
+  bool found = false;
+  while (fgets(buf, sizeof(buf), f) != NULL) {
+    if (strncmp(buf, name, namelen) == 0) {
+      found = true;
+      break;
+    }
+  }
+  fclose(f);
+  return found;
+}
+
 static volatile uint32_t *timer1Mhz = NULL;
 
 static void sleep_nanos_rpi_1(long nanos);
@@ -293,6 +309,12 @@ public:
     : triggered_(false) {
     assert(CanHandle(pins));
 
+    if (LinuxHasModuleLoaded("snd_bcm2835")) {
+      fprintf(stderr, "\nsnd_bcm2835: found the sound module to be loaded.\n"
+              "This is known to cause trouble.\n"
+              "See Troubleshooting section in README how to disable.\n\n");
+    }
+
     for (size_t i = 0; i < specs.size(); ++i) {
       sleep_hints_.push_back(specs[i] / 1000);
     }