From 4f0f3dfb410062db4d41e42c2c7cff6c8b48f071 Mon Sep 17 00:00:00 2001
From: Jeremy Herbert <jeremy.006@gmail.com>
Date: Mon, 4 Nov 2019 01:25:16 -0800
Subject: [PATCH] drivers/sdcard: Raise exception on timeout of readinto.

Otherwise the code can get stuck in an infinite loop if the SD card fails
to respond to a read.
---
 drivers/sdcard/sdcard.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/sdcard/sdcard.py b/drivers/sdcard/sdcard.py
index ffc551d9ae..fc67875566 100644
--- a/drivers/sdcard/sdcard.py
+++ b/drivers/sdcard/sdcard.py
@@ -172,10 +172,13 @@ class SDCard:
         self.cs(0)
 
         # read until start byte (0xff)
-        while True:
+        for i in range(_CMD_TIMEOUT):
             self.spi.readinto(self.tokenbuf, 0xff)
             if self.tokenbuf[0] == _TOKEN_DATA:
                 break
+        else:
+            self.cs(1)
+            raise OSError("timeout waiting for response")
 
         # read data
         mv = self.dummybuf_memoryview