diff --git a/BaS_gcc/Makefile b/BaS_gcc/Makefile
index 20b3a96..d614d97 100644
--- a/BaS_gcc/Makefile
+++ b/BaS_gcc/Makefile
@@ -71,7 +71,8 @@ CSRCS= \
 	$(SRCDIR)/sd_card.c \
 	$(SRCDIR)/wait.c \
 	$(SRCDIR)/s19reader.c \
-	$(SRCDIR)/flash.c
+	$(SRCDIR)/flash.c \
+	$(SRCDIR)/xhdi_sd.c
 
 ASRCS= \
 	$(SRCDIR)/startcf.S \
@@ -137,6 +138,9 @@ $(LIBBAS): $(OBJS)
 	$(AR) rv $@ $(OBJS)
 	$(RANLIB) $@
 	
+# compile xhdi_sd.c with -mshort to adhere to TOS argument passing conventions
+$(OBJDIR)/xhdi_sd.o: CFLAGS += -mshort
+
 # compile init_fpga with -mbitfield for testing purposes
 #$(OBJDIR)/init_fpga.o:	CFLAGS += -mbitfield
 
diff --git a/BaS_gcc/include/xhdi_sd.h b/BaS_gcc/include/xhdi_sd.h
new file mode 100644
index 0000000..5add10a
--- /dev/null
+++ b/BaS_gcc/include/xhdi_sd.h
@@ -0,0 +1,55 @@
+/*
+ * xhdi_sd.h
+ *
+ *  Created on: 01.05.2013
+ *      Author: mfro
+ */
+#ifndef _XHDI_SD_H_
+#define _XHDI_SD_H_
+
+/*
+ * FIXME: dangerous TRAP here!
+ *
+ * all of these functions get compiled with "normal" GCC integers (32 bit). However, since they will be called
+ * from code compiled with -mshort, integers must be declared uint32_t for those compilation units to adhere
+ * to "normal" GCC calling conventions.
+ *
+ * This is ugly and slow (all stack frames from -mshort compiled code need to be rearranged for "normal"
+ * calling conventions), but that's the way it currently is...
+ *
+ */
+#ifdef __MSHORT__
+#define UINT16_T	uint32_t
+#else
+#define UINT16_T	uint16_t
+#endif
+
+extern uint32_t xhdi_call(int xhdi_fun, ...);
+
+extern uint32_t xhdi_version(void);	/* XHDI 0 */
+extern uint32_t xhdi_inquire_target(uint32_t major, uint32_t minor, uint32_t block_size, uint32_t flags,
+		char *product_name);		/* XHDI 1 */
+extern uint32_t xhdi_reserve(UINT16_T major, UINT16_T minor, UINT16_T do_reserve, UINT16_T key);	/* XHDI 2 */
+extern uint32_t xhdi_lock(UINT16_T major, UINT16_T minor, UINT16_T do_lock, UINT16_T key);	/* XHDI 3 */
+extern uint32_t xhdi_stop(UINT16_T major, UINT16_T minor, UINT16_T do_lock, UINT16_T key);	/* XHDI 4 */
+extern uint32_t xhdi_eject(UINT16_T major, UINT16_T minor, UINT16_T do_eject, UINT16_T key);	/* XHDI 5 */
+extern uint32_t xhdi_drivemap(void);	/* XHDI 6 */
+extern uint32_t xhdi_inquire_device(UINT16_T bios_device, UINT16_T *major, UINT16_T *minor,
+        uint32_t *start_sector, /* BPB */ void *bpb);	/* XHDI 7 */
+extern uint32_t xhdi_inquire_driver(UINT16_T bios_device, char *name, char *version,
+		char *company, UINT16_T *ahdi_version, UINT16_T *maxIPL);	/* XHDI 8 */
+extern uint32_t xhdi_new_cookie(void *newcookie);	/* XHDI 9 */
+extern uint32_t xhdi_read_write(UINT16_T major, UINT16_T minor, UINT16_T rwflag,
+        uint32_t recno, UINT16_T count, void *buf);	/* XHDI 10 */
+extern uint32_t xhdi_inquire_target2(UINT16_T major, UINT16_T minor, uint32_t *block_size,
+        uint32_t *device_flags, char *product_name, UINT16_T stringlen);	/* XHDI 11 */
+extern uint32_t xhdi_inquire_device2(UINT16_T bios_device, UINT16_T *major, UINT16_T *minor,
+        UINT16_T *start_sector, /* BPB */ void *bpb, uint32_t *blocks, char *partid); /* XHDI 12 */
+extern uint32_t xhdi_driver_special(uint32_t key1, uint32_t key2, UINT16_T subopcode, void *data); /* XHDI 13 */
+extern uint32_t xhdi_get_capacity(UINT16_T major, UINT16_T minor, uint32_t *blocks, uint32_t *bs); /* XHDI 14 */
+extern uint32_t xhdi_medium_changed(UINT16_T major, UINT16_T minor);	/* XHDI 15 */
+extern uint32_t xhdi_mint_info(UINT16_T opcode, void *data);			/* XHDI 16 */
+extern uint32_t xhdi_dos_limits(UINT16_T which, uint32_t limit);		/* XHDI 17 */
+extern uint32_t xhdi_last_access(UINT16_T major, UINT16_T minor, uint32_t *ms);	/* XHDI 18 */
+
+#endif /* _XHDI_SD_H_ */
diff --git a/BaS_gcc/sources/xhdi_sd.c b/BaS_gcc/sources/xhdi_sd.c
new file mode 100644
index 0000000..ec60a48
--- /dev/null
+++ b/BaS_gcc/sources/xhdi_sd.c
@@ -0,0 +1,118 @@
+/*
+ * xhdi_sd.c
+ *
+ *  Created on: 01.05.2013
+ *      Author: mfro
+ */
+
+#include <stdint.h>
+#include <stdarg.h>
+
+#include "xhdi_sd.h"
+#include "bas_printf.h"
+
+uint32_t xhdi_call(int xhdi_fun, ...)
+{
+	va_list arguments;
+	va_start(arguments, xhdi_fun);
+
+	switch(xhdi_fun)
+	{
+	case 0:
+		return xhdi_version();
+		break;
+
+	case 1:
+	{
+		uint16_t major;
+		uint16_t minor;
+		uint32_t block_size;
+		uint32_t flags;
+		char *product_name;
+
+		major = va_arg(arguments, unsigned int);
+		minor = va_arg(arguments, unsigned int);
+		block_size = va_arg(arguments, uint32_t);
+		flags = va_arg(arguments, uint32_t);
+		product_name = va_arg(arguments, char *);
+		return xhdi_inquire_target((uint32_t) major, (uint32_t) minor, block_size, flags,
+				product_name);
+	}
+		break;
+
+#ifdef test
+	case 2:
+
+		return xhdi_reserve();
+		break;
+
+	case 3:
+		return xhdi_lock();
+		break;
+
+	case 4:
+		return xhdi_stop();
+		break;
+
+	case 5:
+		return xhdi_eject();
+		break;
+
+	case 6:
+		return xhdi_drivemap();
+		break;
+
+	case 7:
+		return xhdi_inquire_device();
+		break;
+
+	case 8:
+		return xhdi_inquire_driver();
+		break;
+
+	case 9:
+		return xhdi_new_cookie();
+		break;
+
+	case 10:
+		return xhdi_read_write();
+		break;
+
+	case 11:
+		return xhdi_inquire_target2();
+		break;
+
+	case 12:
+		return xhdi_inquire_device2();
+		break;
+
+	case 13:
+		return xhdi_driver_special();
+		break;
+
+	case 14:
+		return xhdi_get_capacity();
+		break;
+
+	case 15:
+		return xhdi_medium_changed();
+		break;
+
+	case 16:
+		return xhdi_mint_info();
+		break;
+
+	case 17:
+		return xhdi_dos_limits();
+		break;
+
+	case 18:
+		return xhdi_last_access();
+		break;
+#endif
+	default:
+		;
+	}
+	xprintf("unknown XHDI function %d\r\n");
+	return -32;
+}