00 - Semihosting

Minimal semihosted ARM Cortex-M "Hello World"

00-Semihosting/Makefile

@@ -0,0 +1,22 @@
+CROSS_COMPILE ?= arm-none-eabi-
+CC := $(CROSS_COMPILE)gcc
+CFLAGS = -fno-common -O0 -std=gnu99 \
+	 -mcpu=cortex-m3 -mthumb \
+	 -T semi.ld -nostartfiles \
+
+TARGET = semi.bin
+all: $(TARGET)
+
+$(TARGET): semi.c startup.c
+	$(CC) $(CFLAGS) $^ -o semi.elf
+	$(CROSS_COMPILE)objcopy -Obinary semi.elf semi.bin
+	$(CROSS_COMPILE)objdump -S semi.elf > semi.list
+
+qemu: $(TARGET)
+	@qemu-system-arm -M ? | grep stm32-p103 >/dev/null || exit
+	@echo "Press Ctrl-A and then X to exit QEMU"
+	@echo
+	qemu-system-arm -M stm32-p103 -semihosting -nographic -kernel semi.bin
+
+clean:
+	rm -f *.o *.bin *.elf *.list

00-Semihosting/semi.c

@@ -0,0 +1,23 @@
+#include <stdint.h>
+
+static int semihost_call(int service, void *opaque)
+{
+	register int r0 asm("r0") = service;
+	register void *r1 asm("r1") = opaque;
+	register int result asm("r0");
+	asm volatile("bkpt 0xab"
+	             : "=r" (result) : "r" (r0), "r" (r1));
+	return result;
+}
+
+enum SEMIHOST_SVC {
+	SYS_WRITE = 0x05,
+};
+
+void main(void)
+{
+	char message[] = "Hello World!\n";
+	uint32_t param[] = { 1, (uint32_t) message, sizeof(message) };
+	semihost_call(SYS_WRITE, (void *) param);
+	while (1);
+}

00-Semihosting/semi.ld

@@ -0,0 +1,15 @@
+ENTRY(reset_handler)
+
+MEMORY
+{
+	FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 128K
+}
+
+SECTIONS
+{
+	.text :
+	{
+		KEEP(*(.isr_vector))
+		*(.text)
+	} >FLASH
+}

00-Semihosting/startup.c

@@ -0,0 +1,14 @@
+#include <stdint.h>
+
+extern void main(void);
+void reset_handler(void)
+{
+	/* jump to C entry point */
+	main();
+}
+
+__attribute((section(".isr_vector")))
+uint32_t *isr_vectors[] = {
+	0,
+	(uint32_t *) reset_handler,	/* code entry point */
+};

README.md

@@ -17,6 +17,8 @@ make
 
 Steps
 -----
+* `00-Semihosting`
+  - Minimal semihosted ARM Cortex-M "Hello World"
 * `00-HelloWorld`
   - Enable STM32 USART to print trivial greetings
 * `01-HelloWorld`