[PATCH] user: Document Zynq network

[Sebastian Huber]

Content is from rtems-libbsd/libbsd.txt with minor modifications.
---
 user/bsps/arm/xilinx-zynq.rst | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/user/bsps/arm/xilinx-zynq.rst b/user/bsps/arm/xilinx-zynq.rst
index 29f9cb0..0ac4487 100644
--- a/user/bsps/arm/xilinx-zynq.rst
+++ b/user/bsps/arm/xilinx-zynq.rst
@@ -1,6 +1,6 @@
 .. SPDX-License-Identifier: CC-BY-SA-4.0
 
-.. Copyright (C) 2020 Chris Johns (chrisj at rtems.org)
+.. Copyright (C) 2015, 2020 Chris Johns (chrisj at rtems.org)
 
 xilinx-zynq
 ===========
@@ -49,6 +49,22 @@ tools or a bootloader will be overwritten.
 The settings for the console driver can be changed by the user
 application through the termios API afterwards.
 
+Network
+-------
+
+The Cadence network interface driver of LibBSD works on the Xilinx Zynq
+platform. The hardware checksum support works on real hardware but does not
+seem to be supported on Qemu therefore the default state is to disable
+``IFCAP_TXCSUM`` and ``IFCAP_RXCSUM`` and this can be enabled from the shell
+with:
+
+.. code-block:: none
+
+    ifconfig cgem0 rxcsum txcsum
+
+or with an ``ioctl()`` call to the network interface driver with ``SIOCSIFCAP``
+and the mask ``IFCAP_TXCSUM`` and ``IFCAP_RXCSUM`` set.
+
 Debugging with xilinx_zynq_a9_qemu
 ----------------------------------
 
-- 
2.35.3