From ca2c3d86e2baf96ca8f128b3e813e736cff5d7d2 Mon Sep 17 00:00:00 2001
From: gazhank <gazhank@gmail.com>
Date: Sat, 1 May 2021 17:05:02 +0100
Subject: [PATCH 1/2] fix set and get methods for low_latency

---
 packages/bindings/src/serialport_linux.cpp | 21 ++++++++++-
 packages/bindings/src/serialport_linux.h   |  1 +
 packages/bindings/src/serialport_unix.cpp  | 43 +++++++++++-----------
 3 files changed, 41 insertions(+), 24 deletions(-)

diff --git a/packages/bindings/src/serialport_linux.cpp b/packages/bindings/src/serialport_linux.cpp
index 01fc222f9..d33baf865 100755
--- a/packages/bindings/src/serialport_linux.cpp
+++ b/packages/bindings/src/serialport_linux.cpp
@@ -43,6 +43,8 @@ int linuxSetLowLatencyMode(const int fd, const bool enable) {
   if (ioctl(fd, TIOCGSERIAL, &ss)) {
     return -1;
   }
+  
+  int oldFlags = ss.flags;
 
   if (enable) {
     ss.flags |= ASYNC_LOW_LATENCY;
@@ -50,10 +52,25 @@ int linuxSetLowLatencyMode(const int fd, const bool enable) {
     ss.flags &= ~ASYNC_LOW_LATENCY;
   }
 
-  if (ioctl(fd, TIOCSSERIAL, &ss)) {
-    return -2;
+  if (oldFlags != ss.flags)
+  {
+    if (ioctl(fd, TIOCSSERIAL, &ss)) {
+      return -2;
+    }
+  }
+
+  return 0;
+}
+
+int linuxGetLowLatencyMode(const int fd, bool* const enabled) {
+  struct serial_struct ss;
+
+  if (ioctl(fd, TIOCGSERIAL, &ss)) {
+    return -1;
   }
 
+  *enabled = ss.flags & ASYNC_LOW_LATENCY;
+
   return 0;
 }
 
diff --git a/packages/bindings/src/serialport_linux.h b/packages/bindings/src/serialport_linux.h
index 2aff3bb18..f6eb928f2 100755
--- a/packages/bindings/src/serialport_linux.h
+++ b/packages/bindings/src/serialport_linux.h
@@ -4,6 +4,7 @@
 int linuxSetCustomBaudRate(const int fd, const unsigned int baudrate);
 int linuxGetSystemBaudRate(const int fd, int* const outbaud);
 int linuxSetLowLatencyMode(const int fd, const bool enable);
+int linuxGetLowLatencyMode(const int fd, bool* const enabled);
 
 #endif  // PACKAGES_SERIALPORT_SRC_SERIALPORT_LINUX_H_
 
diff --git a/packages/bindings/src/serialport_unix.cpp b/packages/bindings/src/serialport_unix.cpp
index 07c5d8354..d8cf37b30 100644
--- a/packages/bindings/src/serialport_unix.cpp
+++ b/packages/bindings/src/serialport_unix.cpp
@@ -332,19 +332,6 @@ void EIO_Set(uv_work_t* req) {
     bits |= TIOCM_DSR;
   }
 
-  #if defined(__linux__)
-  if (data->lowLatency) {
-    int err = linuxSetLowLatencyMode(data->fd, data->lowLatency);
-    if (err == -1) {
-      snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot get", strerror(errno));
-      return;
-    } else if(err == -2) {
-      snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot set", strerror(errno));
-      return;
-    }
-  }
-  #endif
-
   int result = 0;
   if (data->brk) {
     result = ioctl(data->fd, TIOCSBRK, NULL);
@@ -361,6 +348,17 @@ void EIO_Set(uv_work_t* req) {
     snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot set", strerror(errno));
     return;
   }
+
+  #if defined(__linux__)
+  int err = linuxSetLowLatencyMode(data->fd, data->lowLatency);
+  if (err == -1) {
+    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot get", strerror(errno));
+    return;
+  } else if(err == -2) {
+    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot set", strerror(errno));
+    return;
+}
+  #endif
 }
 
 void EIO_Get(uv_work_t* req) {
@@ -372,19 +370,20 @@ void EIO_Get(uv_work_t* req) {
     return;
   }
 
-  data->lowLatency = false;
+  data->cts = bits & TIOCM_CTS;
+  data->dsr = bits & TIOCM_DSR;
+  data->dcd = bits & TIOCM_CD;
+
   #if defined(__linux__) && defined(ASYNC_LOW_LATENCY)
-  int latency_bits;
-  if (-1 == ioctl(data->fd, TIOCGSERIAL, &latency_bits)) {
-    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot get", strerror(errno));
+  bool lowlatency = false;
+  if (-1 == linuxGetLowLatencyMode(data->fd, &lowlatency)) {
+    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot get low latency", strerror(errno));
     return;
   }
-  data->lowLatency = latency_bits & ASYNC_LOW_LATENCY;
+  data->lowLatency = lowlatency;
+  #else
+  data->lowLatency = false;
   #endif
-
-  data->cts = bits & TIOCM_CTS;
-  data->dsr = bits & TIOCM_DSR;
-  data->dcd = bits & TIOCM_CD;
 }
 
 void EIO_GetBaudRate(uv_work_t* req) {

From 73107516e34f720e69528645016a70f3e28a40f8 Mon Sep 17 00:00:00 2001
From: gazhank <gazhank@gmail.com>
Date: Sat, 1 May 2021 17:10:48 +0100
Subject: [PATCH 2/2] clarify error messages

---
 packages/bindings/src/serialport_unix.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/bindings/src/serialport_unix.cpp b/packages/bindings/src/serialport_unix.cpp
index d8cf37b30..62b42597f 100644
--- a/packages/bindings/src/serialport_unix.cpp
+++ b/packages/bindings/src/serialport_unix.cpp
@@ -352,10 +352,10 @@ void EIO_Set(uv_work_t* req) {
   #if defined(__linux__)
   int err = linuxSetLowLatencyMode(data->fd, data->lowLatency);
   if (err == -1) {
-    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot get", strerror(errno));
+    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot get low latency", strerror(errno));
     return;
   } else if(err == -2) {
-    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot set", strerror(errno));
+    snprintf(data->errorString, sizeof(data->errorString), "Error: %s, cannot set low latency", strerror(errno));
     return;
 }
   #endif