From b4b80f1f6e59fa02d508af860f1a572c9224b975 Mon Sep 17 00:00:00 2001
From: Josh Blum <josh@joshknows.com>
Date: Tue, 15 Jun 2010 01:23:00 +0000
Subject: usrp-e: added poll(...) call before read(...) call

---
 host/lib/usrp/usrp_e/io_impl.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'host/lib')

diff --git a/host/lib/usrp/usrp_e/io_impl.cpp b/host/lib/usrp/usrp_e/io_impl.cpp
index e1c1fe80b..829e923b5 100644
--- a/host/lib/usrp/usrp_e/io_impl.cpp
+++ b/host/lib/usrp/usrp_e/io_impl.cpp
@@ -22,6 +22,7 @@
 #include <fcntl.h> //read, write
 #include <linux/usrp_e.h> //transfer frame struct
 #include <stddef.h> //offsetof
+#include <poll.h>
 #include <boost/format.hpp>
 #include <iostream>
 
@@ -75,12 +76,22 @@ private:
         //std::cout << boost::format(
         //    "calling read on fd %d, buff size is %d"
         //) % _fd % boost::asio::buffer_size(buff) << std::endl;
+
+        //setup and call poll on the file descriptor
+        //return 0 and do not read when poll times out
+        pollfd pfd;
+        pfd.fd = _fd;
+        pfd.events = POLLIN;
+        if (poll(&pfd, 1, 100 /*ms*/) <= 0) return 0; //timeout
+
+        //perform the blocking read(...)
         ssize_t ret = read(
             _fd,
             boost::asio::buffer_cast<void *>(buff),
             boost::asio::buffer_size(buff)
         );
         if (ret < ssize_t(sizeof(usrp_transfer_frame))) return 0;
+
         //overwrite the vrt header length with the transfer frame length
         size_t frame_size = boost::asio::buffer_cast<usrp_transfer_frame *>(buff)->len;
         boost::uint32_t *vrt_header = boost::asio::buffer_cast<boost::uint32_t *>(buff) + vrt_header_offset_words32;
-- 
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