device3: Constraint send/recv_frame_size based on down/upstream MTU

We need to properly contraint the send/recv_frame_size based on the
minimum MTU of all the down/upstream blocks. This fixes the issue with
E310 tx/rx streaming as it has smaller MTU sizes than the other usrps.

1 files changed, 6 insertions, 2 deletions

diff --git a/host/lib/rfnoc/block_ctrl_base.cpp b/host/lib/rfnoc/block_ctrl_base.cpp
index ed8068b5b..e70267b96 100644
--- a/host/lib/rfnoc/block_ctrl_base.cpp
+++ b/host/lib/rfnoc/block_ctrl_base.cpp
@@ -94,12 +94,16 @@ block_ctrl_base::block_ctrl_base(const make_args_t& make_args)
         // Set source addresses:
         sr_write(SR_BLOCK_SID, get_address(ctrl_port), ctrl_port);
         // Set sink buffer sizes:
-        settingsbus_reg_t reg = SR_READBACK_REG_FIFOSIZE;
-        size_t buf_size_bytes = size_t(sr_read64(reg, ctrl_port));
+        settingsbus_reg_t reg_fifo = SR_READBACK_REG_FIFOSIZE;
+        size_t buf_size_bytes      = size_t(sr_read64(reg_fifo, ctrl_port));
         if (buf_size_bytes > 0)
             n_valid_input_buffers++;
         _tree->create<size_t>(_root_path / "input_buffer_size" / ctrl_port)
             .set(buf_size_bytes);
+        // Set MTU size and convert to bytes:
+        settingsbus_reg_t reg_mtu = SR_READBACK_REG_MTU;
+        size_t mtu                = 8 * (1 << size_t(sr_read64(reg_mtu, ctrl_port)));
+        _tree->create<size_t>(_root_path / "mtu" / ctrl_port).set(mtu);
         // Set default destination SIDs
         // Otherwise, the default is someone else's SID, which we don't want
         sr_write(SR_RESP_IN_DST_SID, 0xFFFF, ctrl_port);