Set WAIT_ECHO false if on a nexus test.

Tested: https://louhi.dev/4676813492322304/execution-detail/5696967535099904

Bypass-Presubmit-Reason: no presubmits

Change-Id: I2c280cd1d5345b6f0b4e4756e32b72c3d61f0098

FPGALibrary.py

diff --git a/FPGALibrary.py b/FPGALibrary.py
index 8e8f1a9..6da0e8a 100644
--- a/FPGALibrary.py
+++ b/FPGALibrary.py
@@ -256,7 +256,7 @@
           waitForEcho: boolean. Deafults to True. Whether or not to check
             echoed back characters against the given string.
         """
-        if kwargs.get('waitForEcho'):
+        if 'waitForEcho' in kwargs:
             self._write_line_to_uart(self.default_uart,
                                      line,
                                      wait_for_echo=kwargs['waitForEcho'])

shodan_boot.robot

diff --git a/shodan_boot.robot b/shodan_boot.robot
index 1633b2a..4b96e47 100644
--- a/shodan_boot.robot
+++ b/shodan_boot.robot
@@ -62,7 +62,6 @@
 
 # TODO b/329673199 test is flaky on nexus platform
 Test SDK + TimerService (oneshot & periodic)
-    Skip if                     "${PLATFORM}" == "nexus"
     Requires                    shodan-bootup
     Install App                 timer
     Wait For Line On Uart       sdk_timer_cancel returned Err(SDKInvalidTimer) with nothing running

variables/common.py

diff --git a/variables/common.py b/variables/common.py
index a9a1f72..ef57475 100644
--- a/variables/common.py
+++ b/variables/common.py
@@ -32,6 +32,10 @@
 ROOTDIR  = environ['ROOTDIR']
 PLATFORM = environ['PLATFORM']
 
+# To avoid race conditions, do not wait for strings to echo back on nexus tests.
+if PLATFORM == "nexus":
+  WAIT_ECHO = False
+
 CANTRIP_OUTDIR = f'{ROOTDIR}/out/cantrip/{PLATFORM}/{BUILD_TYPE}'
 
 SCRIPT             = f'{ROOTDIR}/sim/config/{PLATFORM}.resc'