pkg/tinydtls: allow build for AVR

[benpicco]

Contribution description

tinyDTLS builds and works just fine on AVR, we only have to disable the custom logging functions as those will try to call printf() with non-literal strings. (We don't even call them, but they get built anyway)

Testing procedure

I used tests/nanocoap_cli for testing. As THREAD_STACKSIZE_DEFAULT is lower on AVR we have to bump the main stack size here:

--- a/tests/nanocoap_cli/Makefile
+++ b/tests/nanocoap_cli/Makefile
@@ -43,7 +43,7 @@ ifeq (,$(filter $(BOARD),$(LOW_MEMORY_BOARDS)))
   USEMODULE += shell_cmds_default
 
   # DTLS and VFS operations require more stack on the main thread
-  CFLAGS += -DTHREAD_STACKSIZE_MAIN=\(3*THREAD_STACKSIZE_DEFAULT\)
+  CFLAGS += -DTHREAD_STACKSIZE_MAIN=\(5*THREAD_STACKSIZE_DEFAULT\)
 
   # always enable auto-format for native
   ifeq ($(BOARD),native)

I ran a border router on samr21-xpro with

sudo dist/tools/tapsetup/tapsetup -u eno1
make BOARD=samr21-xpro REUSE_TAP=1 flash term

and examples/gcoap_dtls on native on the tap1 port. I then connected from the avr-rss2 to the native instance via the samr21-xpro border router:

> ncget coaps://[2001:9e8:1400:e100:58b0:8ff:fe67:ad82]/.well-known/core -
2023-03-04 23:06:02,562 # </cli/stats>;ct=0;rt="count";obs,</riot/board>

> ncget coaps://[2001:9e8:1400:e100:58b0:8ff:fe67:ad82]/riot/board -
2023-03-04 23:06:14,386 # netq_node_new: malloc
2023-03-04 23:06:14,390 # cannot add alert, retransmit buffer full
2023-03-04 23:06:14,434 # unexpected ChangeCipherSpec during handshake
2023-03-04 23:06:14,447 # No security context for epoch: 1 (handshake)
2023-03-04 23:06:14,487 # No security context for epoch: 1 (alert)
2023-03-04 23:06:15,981 # No security context for epoch: 1 (handshake)
2023-03-04 23:06:16,411 # netq_node_new: malloc
2023-03-04 23:06:16,416 # cannot add alert, retransmit buffer full
2023-03-04 23:06:16,713 # No security context for epoch: 1 (alert)
2023-03-04 23:06:19,993 # native

Issues/PRs references

upstream PR to no build custom logging functions: eclipse/tinydtls#189

[riot-ci]

Murdock results

✔️ PASSED

824d2f8 tests: update Makefile.ci where tinyDTLS is used

Success	Failures	Total	Runtime
6931	0	6931	10m:34s

Artifacts

• Documentation preview

[maribu]

Looks like only some Makefile.ci updstes are needed to get this in

[benpicco]

bors try

[bors]

try

Build failed:

• Murdock

[benpicco]

bors merge

[bors]

Build succeeded:

• Murdock
• static-tests
• tools-build-success