fw/defaultapp: Introduce simple default app

To retain the default behaviour from Bellatrix, we introduce a simple
default app. If used on flash app slot 0 we get the same behaviour as
in Bellatrix, that is, waiting for an app from the client.

hw/application_fpga/fw/README.md

@@ -794,6 +794,9 @@ $ picocom /dev/ttyACM1
 
 or similar.
 
+- `fw/defaultapp`: Immediately resets the TKey with the intention to
+  start an app from the client, replicating the behaviour of earlier
+  generations.
 - `fw/testapp`: Runs through a couple of tests that are now impossible
   to do in the `testfw`.
 - `fw/reset_test`: Interactively test different reset scenarios.

hw/application_fpga/fw/defaultapp/Makefile

@@ -0,0 +1,73 @@
+P := $(shell dirname $(realpath $(lastword $(MAKEFILE_LIST))))
+LIBDIR ?= ../../tkey-libs
+OBJCOPY ?= llvm-objcopy
+CC = clang
+CFLAGS = \
+	-target riscv32-unknown-none-elf \
+	-march=rv32iczmmul \
+	-mabi=ilp32 \
+	-mcmodel=medany \
+	-static \
+	-std=gnu99 \
+	-Os \
+	-ffast-math \
+	-fno-common \
+	-fno-builtin-printf \
+	-fno-builtin-putchar \
+	-fno-builtin-memcpy \
+	-nostdlib \
+	-mno-relax \
+	-Wall \
+	-Wpedantic \
+	-Wno-language-extension-token \
+	-Werror \
+	-flto \
+	-g \
+	-I $(LIBDIR)/include \
+	-I $(LIBDIR)
+
+AS = clang
+
+ASFLAGS = \
+	-target riscv32-unknown-none-elf \
+	-march=rv32iczmmul \
+	-mabi=ilp32 \
+	-mno-relax
+
+LDFLAGS = \
+	-T $(LIBDIR)/app.lds \
+	-L $(LIBDIR) -lcrt0 -lcommon -lmonocypher -lblake2s
+
+.PHONY: all
+all: defaultapp.bin
+
+# Turn elf into bin for device
+%.bin: %.elf
+	$(OBJCOPY) --input-target=elf32-littleriscv --output-target=binary $^ $@
+	chmod a-x $@
+
+.PHONY: tkey-libs
+tkey-libs:
+	make -C $(LIBDIR)
+
+DEFAULTAPP_FMTFILES = *.[ch]
+
+DEFAULTAPP_OBJS = \
+	$(P)/main.o \
+	../testapp/syscall.o \
+
+defaultapp.elf: tkey-libs $(DEFAULTAPP_OBJS)
+	$(CC) $(CFLAGS) $(DEFAULTAPP_OBJS) $(LDFLAGS) -o $@
+
+.PHONY: fmt
+fmt:
+	clang-format --dry-run --ferror-limit=0 $(DEFAULTAPP_FMTFILES)
+	clang-format --verbose -i $(DEFAULT_FMTFILES)
+
+.PHONY: checkfmt
+checkfmt:
+	clang-format --dry-run --ferror-limit=0 --Werror $(DEFAULT_FMTFILES)
+
+.PHONY: clean
+clean:
+	rm -f defaultapp.* $(DEFAULTAPP_OBJS)

hw/application_fpga/fw/defaultapp/main.c

@@ -0,0 +1,19 @@
+// Copyright (C) 2025 - Tillitis AB
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <tkey/debug.h>
+#include <tkey/led.h>
+
+#include "../testapp/syscall.h"
+#include "../tk1/reset.h"
+#include "../tk1/syscall_num.h"
+
+int main(void)
+{
+	struct reset rst = {0};
+
+	led_set(LED_BLUE);
+
+	rst.type = START_CLIENT;
+	syscall(TK1_SYSCALL_RESET, (uint32_t)&rst, 0, 0);
+}