From 5e47fc7e22eb81389cd9eee909efe490b688ea57 Mon Sep 17 00:00:00 2001
From: Francisco Molina <femolina@uc.cl>
Date: Tue, 14 Dec 2021 18:43:53 +0100
Subject: [PATCH] cpu: do not auto-select ztimer_periph_rtt for sam0, fe310

The sam0 rtt busy loops for 180us every time an alarm is set or
the counter is read, this propagates and leads to timing errors
on ztimer_msec that are higher than > +-1msec.

The same goes for fe310.
---
 cpu/fe310/Kconfig       |  1 +
 cpu/sam0_common/Kconfig |  1 +
 cpu/sam3/Kconfig        |  1 +
 sys/ztimer/Makefile.dep | 11 +++++++++++
 4 files changed, 14 insertions(+)

diff --git a/cpu/fe310/Kconfig b/cpu/fe310/Kconfig
index 9ba0b39870..25c61c6c64 100644
--- a/cpu/fe310/Kconfig
+++ b/cpu/fe310/Kconfig
@@ -21,6 +21,7 @@ config CPU_FAM_FE310
     select MODULE_PERIPH_PLIC if TEST_KCONFIG
     select MODULE_PERIPH_CORETIMER if MODULE_PERIPH_TIMER && HAS_PERIPH_CORETIMER
     select MODULE_PERIPH_RTT if MODULE_PERIPH_RTC && HAS_PERIPH_RTT
+    select MODULE_ZTIMER_NO_PERIPH_RTT if TEST_KCONFIG && MODULE_ZTIMER
 
 config CPU_MODEL_FE310_G000
     bool
diff --git a/cpu/sam0_common/Kconfig b/cpu/sam0_common/Kconfig
index 02a6150e6d..0436401e66 100644
--- a/cpu/sam0_common/Kconfig
+++ b/cpu/sam0_common/Kconfig
@@ -26,6 +26,7 @@ config CPU_COMMON_SAM0
     select HAS_PERIPH_WDT_CB
     select HAS_PERIPH_WDT_WARNING_PERIOD
     select HAVE_SHARED_PERIPH_RTT_PERIPH_RTC
+    select MODULE_ZTIMER_NO_PERIPH_RTT if TEST_KCONFIG && MODULE_ZTIMER
 
 if CPU_COMMON_SAM0
 
diff --git a/cpu/sam3/Kconfig b/cpu/sam3/Kconfig
index d42f79c963..9f8b0da840 100644
--- a/cpu/sam3/Kconfig
+++ b/cpu/sam3/Kconfig
@@ -12,6 +12,7 @@ config CPU_FAM_SAM3
     select HAS_CPU_SAM3
     select HAS_PERIPH_CPUID
     select HAS_PERIPH_HWRNG
+    select MODULE_ZTIMER_NO_PERIPH_RTT if TEST_KCONFIG && MODULE_ZTIMER
 
 ## CPU Models
 config CPU_MODEL_SAM3X8E
diff --git a/sys/ztimer/Makefile.dep b/sys/ztimer/Makefile.dep
index 1042f47e27..928fe13b10 100644
--- a/sys/ztimer/Makefile.dep
+++ b/sys/ztimer/Makefile.dep
@@ -78,6 +78,17 @@ ifneq (,$(filter ztimer_usec,$(USEMODULE)))
   USEMODULE += ztimer_periph_timer
 endif
 
+# NOTE: select the module here and not in the CPU so that order of inclusion
+# does not have periph_rtt selected earlier that it should be while at the same
+# time avoiding the module 'ztimer-no_periph_rtt' being included unecesarily.
+# The sam0 rtt busy loops for 180us every time an alarm is set or
+# the counter is read, this propagates and leads to timing errors
+# on ztimer_msec that are higher than > +-1msec.
+# The same goes for the fe310 rtt.
+ifneq (,$(filter sam% fe310,$(CPU)))
+  USEMODULE += ztimer_no_periph_rtt
+endif
+
 ifneq (,$(filter ztimer_msec ztimer_sec,$(USEMODULE)))
   USEMODULE += ztimer
   ifeq (,$(filter ztimer_no_periph_rtt,$(USEMODULE)))