Device3: Fix MTU and default frame sizes

The latest changes to the get_*x_stream() functions to calculate the MTU for
the channel caused default frame size values to be ignored.  This change fixes
that by changing the key from "send/recv_frame_size" to "mtu" and then changing
the implementations of make_transport() constrain the frame size values based
on the "mtu" value as well as any device and/or transport-specific limits.

Signed-off-by: Michael West <michael.west@ettus.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/host/lib/usrp/e300/e300_impl.cpp b/host/lib/usrp/e300/e300_impl.cpp
index 5a6376039..fadac719c 100644
--- a/host/lib/usrp/e300/e300_impl.cpp
+++ b/host/lib/usrp/e300/e300_impl.cpp
@@ -706,14 +706,23 @@ uhd::sid_t e300_impl::_allocate_sid(
 uhd::both_xports_t e300_impl::make_transport(
     const uhd::sid_t &address,
     const xport_type_t type,
-    const uhd::device_addr_t &)
+    const uhd::device_addr_t &hints)
 {
     uhd::both_xports_t xports;
     xports.endianness = ENDIANNESS_LITTLE;
 
-    const uhd::transport::zero_copy_xport_params params =
+    uhd::transport::zero_copy_xport_params params =
         (type == CTRL) ? _ctrl_xport_params : _data_xport_params;
 
+    // Constrain frame sizes to MTU if supplied
+    if (type == TX_DATA) {
+        params.send_frame_size = std::min(params.send_frame_size,
+        hints.cast<size_t>("mtu", params.send_frame_size));
+    } else if (type == RX_DATA) {
+        params.recv_frame_size = std::min(params.recv_frame_size,
+        hints.cast<size_t>("mtu", params.recv_frame_size));
+    }
+
     xports.send_sid = _allocate_sid(address);
     xports.recv_sid = xports.send_sid.reversed();
     xports.recv_buff_size = params.recv_frame_size * params.num_recv_frames;