From 6dc9cad2c960f7a011a69b43aeba127678864994 Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sb@m-labs.hk>
Date: Tue, 19 Sep 2017 12:05:12 +0800
Subject: [PATCH] rtio: add explanation about cri.counter

---
 artiq/gateware/rtio/cri.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/artiq/gateware/rtio/cri.py b/artiq/gateware/rtio/cri.py
index f282ae307..7a4359ba7 100644
--- a/artiq/gateware/rtio/cri.py
+++ b/artiq/gateware/rtio/cri.py
@@ -35,6 +35,9 @@ layout = [
     # <0> and <1> are mutually exclusive. <1> has higher priority.
     ("i_status", 3, DIR_S_TO_M),
 
+    # value of the timestamp counter transferred into the CRI clock domain.
+    # monotonic, may lag behind the counter in the IO clock domain, but
+    # not be ahead of it.
     ("counter", 64, DIR_S_TO_M)
 ]