[doc] Mandate specific Vivado version
Vivado 2019.1 is currently not compatible (#89).
Update download description to use Vivado 2018.3.
diff --git a/doc/ug/install_instructions.md b/doc/ug/install_instructions.md
index 63212fb..c64f843 100644
--- a/doc/ug/install_instructions.md
+++ b/doc/ug/install_instructions.md
@@ -162,6 +162,9 @@
### Install Xilinx Vivado
+_**Vivado Version:** Vivado 2019.1 and all its updates are not compatible with this project.
+A discussion on this problem can be found in the [Github issue](https://github.com/lowRISC/opentitan/issues/89)._
+
Vivado can be installed in two ways: either through an "All OS installer Single-File Download", or via the "Linux Self Extracting Web Installer".
Neither option is great:
the "All OS installer" is a huge download of around 20 GB (and the Xilinx download servers seem to be overloaded regularly), but it supports an unattended installation.
@@ -170,9 +173,9 @@
To get started faster we use the web installer in the following.
-1. Go to the [Xilinx download page](https://www.xilinx.com/support/download.html) and download two files for the current version of Vivado.
- (We used Vivado 2018.3 to prepare this guide.)
- 1. The file "Vivado HLx <VERSION>: WebPACK and Editions - Linux Self Extracting Web Installer".
+1. Go to the [Xilinx download page](https://www.xilinx.com/support/download/index.html/content/xilinx/en/downloadNav/vivado-design-tools/2018-3.html) and download two files for Vivado 2018.3.
+ (The version can be chosen on the left side if version 2018.3 is not already selected.)
+ 1. The file "Vivado HLx 2018.3: WebPACK and Editions - Linux Self Extracting Web Installer".
2. The "Digests" file below the download.
