From 9d5a47534d888d00a9a99237cdd018881e179426 Mon Sep 17 00:00:00 2001
From: Karl Fessel <karl.fessel@ovgu.de>
Date: Thu, 3 Mar 2022 13:11:01 +0100
Subject: [PATCH 1/5] sys/Makefile.dep: add fallback timer evaluation

---
 sys/Makefile.dep | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sys/Makefile.dep b/sys/Makefile.dep
index a2343939419f..3d8f84d2086e 100644
--- a/sys/Makefile.dep
+++ b/sys/Makefile.dep
@@ -858,6 +858,13 @@ ifneq (,$(filter evtimer,$(USEMODULE)))
   endif
 endif
 
+ifneq (,$(filter xztimer_fallback,$(USEMODULE)))
+  USEMODULE := $(filter-out xztimer_fallback,$(USEMODULE))
+  ifeq (,$(filter ztimer_usec,$(USEMODULE)))
+    USEMODULE += xtimer
+  endif
+endif
+
 # handle xtimer's deps. Needs to be done *after* ztimer
 ifneq (,$(filter xtimer,$(USEMODULE)))
   include $(RIOTBASE)/sys/xtimer/Makefile.dep

From 24262ade0f752d171fe68ce61f98bc16b6d03b26 Mon Sep 17 00:00:00 2001
From: Karl Fessel <karl.fessel@ovgu.de>
Date: Wed, 23 Feb 2022 16:55:51 +0100
Subject: [PATCH 2/5] net/uhcp: do not require xtimer

---
 sys/Makefile.dep                       | 2 +-
 sys/net/application_layer/uhcp/uhcpc.c | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/sys/Makefile.dep b/sys/Makefile.dep
index 3d8f84d2086e..d4c0da2eead6 100644
--- a/sys/Makefile.dep
+++ b/sys/Makefile.dep
@@ -167,7 +167,7 @@ endif
 
 ifneq (,$(filter uhcpc,$(USEMODULE)))
   USEMODULE += posix_inet
-  USEMODULE += xtimer
+  USEMODULE += xztimer_fallback
 endif
 
 ifneq (,$(filter netdev_tap,$(USEMODULE)))
diff --git a/sys/net/application_layer/uhcp/uhcpc.c b/sys/net/application_layer/uhcp/uhcpc.c
index 1dccdfb3f3b8..9b9d914a370f 100644
--- a/sys/net/application_layer/uhcp/uhcpc.c
+++ b/sys/net/application_layer/uhcp/uhcpc.c
@@ -12,7 +12,11 @@
 #include "net/af.h"
 #include "net/sock/udp.h"
 #include "net/uhcp.h"
+#if IS_USED(MODULE_ZTIMER_USEC)
+#include "ztimer/xtimer_compat.h"
+#else
 #include "xtimer.h"
+#endif
 
 /**
  * @brief Request prefix from uhcp server

From 11e6d2a130aba85ee204c15f9ad81851f24cacef Mon Sep 17 00:00:00 2001
From: Karl Fessel <karl.fessel@ovgu.de>
Date: Wed, 23 Feb 2022 17:29:21 +0100
Subject: [PATCH 3/5] posix/sockets: do not require timer

timer is required by the sock implemetation
---
 sys/Makefile.dep | 1 -
 1 file changed, 1 deletion(-)

diff --git a/sys/Makefile.dep b/sys/Makefile.dep
index d4c0da2eead6..945478c7b21d 100644
--- a/sys/Makefile.dep
+++ b/sys/Makefile.dep
@@ -274,7 +274,6 @@ ifneq (,$(filter posix_sockets,$(USEMODULE)))
   USEMODULE += random
   USEMODULE += vfs
   USEMODULE += posix_headers
-  USEMODULE += xtimer
 endif
 
 ifneq (,$(filter shell,$(USEMODULE)))

From 6c4baee0d23ad41fdddc27485baf9d63a506ceb4 Mon Sep 17 00:00:00 2001
From: Karl Fessel <karl.fessel@ovgu.de>
Date: Wed, 23 Feb 2022 17:41:51 +0100
Subject: [PATCH 4/5] sys/suit_transport_coap: do not require xtimer

---
 sys/Makefile.dep          | 2 +-
 sys/suit/transport/coap.c | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/sys/Makefile.dep b/sys/Makefile.dep
index 945478c7b21d..31d586313f09 100644
--- a/sys/Makefile.dep
+++ b/sys/Makefile.dep
@@ -817,7 +817,7 @@ endif
 
 ifneq (,$(filter suit_transport_coap, $(USEMODULE)))
   USEMODULE += nanocoap_sock
-  USEMODULE += xtimer
+  USEMODULE += xztimer_fallback
   USEMODULE += sock_util
 endif
 
diff --git a/sys/suit/transport/coap.c b/sys/suit/transport/coap.c
index a3a7edf9daf1..4b0ca6b6adde 100644
--- a/sys/suit/transport/coap.c
+++ b/sys/suit/transport/coap.c
@@ -32,7 +32,11 @@
 #include "net/nanocoap_sock.h"
 #include "thread.h"
 #include "periph/pm.h"
+#if IS_USED(MODULE_ZTIMER_USEC)
+#include "ztimer/xtimer_compat.h"
+#else
 #include "xtimer.h"
+#endif
 
 #include "suit/transport/coap.h"
 #include "net/sock/util.h"

From 3cf5f649ac032fa28b7a0629d67a437d87486a35 Mon Sep 17 00:00:00 2001
From: Karl Fessel <karl.fessel@ovgu.de>
Date: Wed, 23 Feb 2022 18:02:46 +0100
Subject: [PATCH 5/5] net/csma_sender:  do not require xtimer

---
 sys/Makefile.dep                             | 2 +-
 sys/net/link_layer/csma_sender/csma_sender.c | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/sys/Makefile.dep b/sys/Makefile.dep
index 31d586313f09..ade4c6521604 100644
--- a/sys/Makefile.dep
+++ b/sys/Makefile.dep
@@ -99,7 +99,7 @@ endif
 
 ifneq (,$(filter csma_sender,$(USEMODULE)))
   USEMODULE += random
-  USEMODULE += xtimer
+  USEMODULE += xztimer_fallback
 endif
 
 ifneq (,$(filter dhcpv6_%,$(USEMODULE)))
diff --git a/sys/net/link_layer/csma_sender/csma_sender.c b/sys/net/link_layer/csma_sender/csma_sender.c
index da95dafd266c..0bb280c78fbd 100644
--- a/sys/net/link_layer/csma_sender/csma_sender.c
+++ b/sys/net/link_layer/csma_sender/csma_sender.c
@@ -22,8 +22,13 @@
 #include <errno.h>
 #include <stdbool.h>
 #include <inttypes.h>
+#include <kernel_defines.h>
 
+#if IS_USED(MODULE_ZTIMER_USEC)
+#include "ztimer/xtimer_compat.h"
+#else
 #include "xtimer.h"
+#endif
 #include "random.h"
 #include "net/netdev.h"
 #include "net/netopt.h"