drivers: add periph_common

This module contains shared functions for periph implementations.

drivers/periph_common/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

drivers/periph_common/spi.c

@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2015 Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @ingroup drivers
+ * @{
+ *
+ * @file
+ * @brief       common SPI function fallback implementations
+ *
+ * @author      Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * @}
+ */
+#include <stddef.h>
+
+#include "board.h"
+#include "cpu.h"
+#include "periph/spi.h"
+#include "periph_cpu.h"
+
+#if SPI_NUMOF
+
+#ifdef PERIPH_SPI_NEEDS_TRANSFER_BYTES
+int spi_transfer_bytes(spi_t dev, char *out, char *in, unsigned int length)
+{
+    int i, trans_ret, trans_bytes = 0;
+    char in_temp;
+
+    for (i = 0; i < length; i++) {
+        if (out != NULL) {
+            trans_ret = spi_transfer_byte(dev, out[i], &in_temp);
+        }
+        else {
+            trans_ret = spi_transfer_byte(dev, 0, &in_temp);
+        }
+        if (trans_ret < 0) {
+            return -1;
+        }
+        if (in != NULL) {
+            in[i] = in_temp;
+        }
+        trans_bytes++;
+    }
+
+    return trans_bytes++;
+}
+#endif
+
+#ifdef PERIPH_SPI_NEEDS_TRANSFER_REG
+int spi_transfer_reg(spi_t dev, uint8_t reg, char out, char *in)
+{
+    int trans_ret;
+
+    trans_ret = spi_transfer_byte(dev, reg, in);
+    if (trans_ret < 0) {
+        return -1;
+    }
+    trans_ret = spi_transfer_byte(dev, out, in);
+    if (trans_ret < 0) {
+        return -1;
+    }
+
+    return 1;
+}
+#endif
+
+#ifdef PERIPH_SPI_NEEDS_TRANSFER_REGS
+int spi_transfer_regs(spi_t dev, uint8_t reg, char *out, char *in, unsigned int length)
+{
+    int trans_ret;
+
+    trans_ret = spi_transfer_byte(dev, reg, in);
+    if (trans_ret < 0) {
+        return -1;
+    }
+    trans_ret = spi_transfer_bytes(dev, out, in, length);
+    if (trans_ret < 0) {
+        return -1;
+    }
+
+    return trans_ret;
+}
+#endif
+
+#endif /* SPI_NUMOF */