# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1612046325 -3600
# Node ID eada6b587c0cbb58e25319417b576e65f1d1957d
# Parent  152c4fc0a9679f2e37abd6faec6fd2ef571ed50e
Avoid needless (but harmless) entry into the read loop when NACK is present.
Added various comments to the I2C driver.

diff -r 152c4fc0a967 -r eada6b587c0c pkg/devices/lib/i2c/src/jz4730.cc
--- a/pkg/devices/lib/i2c/src/jz4730.cc	Sat Jan 16 23:48:09 2021 +0100
+++ b/pkg/devices/lib/i2c/src/jz4730.cc	Sat Jan 30 23:38:45 2021 +0100
@@ -1,7 +1,7 @@
 /*
  * I2C support for the JZ4730.
  *
- * Copyright (C) 2017, 2018, 2020 Paul Boddie <paul@boddie.org.uk>
+ * Copyright (C) 2017, 2018, 2020, 2021 Paul Boddie <paul@boddie.org.uk>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -179,6 +179,8 @@
   if (!set_address(address, true))
     return 0;
 
+  // Wait for an opportunity to begin reading.
+
   do
   {
     if (!wait_for_irq(1000000))
@@ -186,6 +188,16 @@
   }
   while (transferring() || (!data_valid() && !nack()));
 
+  // Device apparently unavailable.
+
+  if (nack())
+  {
+    stop();
+    return nread;
+  }
+
+  // Attempt to read from the device.
+
   while (nread < length)
   {
     do