From a46ab924bdb3fbf9eb65e9b64bd5b47cd3d50ba7 Mon Sep 17 00:00:00 2001
From: Nathaniel Wesley Filardo <nwfilardo@gmail.com>
Date: Wed, 29 Dec 2021 22:34:12 +0000
Subject: [PATCH] Tweaks to i2cu

---
 util/i2cu.lua | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/util/i2cu.lua b/util/i2cu.lua
index 3a59f1d..cfc0f2f 100644
--- a/util/i2cu.lua
+++ b/util/i2cu.lua
@@ -1,7 +1,14 @@
 local self = {}
+local i2c = i2c
+
+function self.probe(bus, addr)
+  i2c.start(bus)
+  local res = i2c.address(bus, addr, i2c.RECEIVER)
+  i2c.stop(bus)
+  return res
+end
 
 function self.readn(bus, addr, len)
-  local i2c = i2c
   i2c.start(bus)
   if not i2c.address(bus, addr, i2c.RECEIVER) then i2c.stop(bus) return nil end
   local v = i2c.read(bus, len)
@@ -10,7 +17,6 @@ function self.readn(bus, addr, len)
 end
 
 function self.writen(bus, addr, ...)
-  local i2c = i2c
   i2c.start(bus)
   if not i2c.address(bus, addr, i2c.TRANSMITTER) then i2c.stop(bus) return nil end
   i2c.write(bus, ...)
@@ -18,13 +24,12 @@ function self.writen(bus, addr, ...)
   return true
 end
 
--- write/read without a full stop/start
+-- write/read without a full stop/start (no risk of losing arbitration)
 function self.wr(bus, addr, len, ...)
-  local i2c = i2c
   i2c.start(bus)
   if not i2c.address(bus, addr, i2c.TRANSMITTER) then i2c.stop(bus) return nil end
   i2c.write(bus, ...)
-  i2c.start(bus)
+  i2c.start(bus) -- "repeated start"
   if not i2c.address(bus, addr, i2c.RECEIVER) then i2c.stop(bus) return nil end
   local v = i2c.read(bus, len)
   i2c.stop(bus)
-- 
2.50.1