Rework specification of SDK and associated dependencies

Ensure that the SDK toolchain is properly pushed through to rootfs.  Note
however that this commit needs the current version of rootfs (at least
commit 13a8096a).

The SDK is now either specified as a single SDK_ROOT key, as before, or as
individual keys for the separate BOOTGEN, BINUTILS_DIR, and possibly
SYSROOT components.

CONFIG.example

@@ -3,12 +3,14 @@
 # Copy this file to CONFIG and edit the settings below to suit your
 # environment.
 
-# Location of rootfs builder.  This needs to be at least version 1.10 and can be
+# Location of rootfs builder.  This needs to be at least version 1.13 and can be
 # downloaded from https://github.com/araneidae/rootfs
-ROOTFS_TOP = /dls_sw/prod/targetOS/rootfs/1-10
+ROOTFS_TOP = /dls_sw/prod/targetOS/rootfs/1.13
 
-# Location of SDK used to build target
-SDK_ROOT = /dls_sw/apps/FPGA/Xilinx/SDK/2015.1
+# Location of SDK used to build target.  There are a couple of ways that this
+# can be specified, depending on precisely where the toolchain is installed.
+# The simplest option is to specify SDK_ROOT.
+SDK_ROOT = /dls_sw/apps/FPGA/Xilinx/SDK/2016.4
 
 # Where to find source files
 TAR_FILES = /dls_sw/prod/targetOS/tar-files

Makefile

@@ -15,10 +15,8 @@ MD5_SUM_linux-xlnx-xilinx-v2015.1  = 930d126df2113221e63c4ec4ce356f2c
 SPHINX_BUILD = sphinx-build
 
 # Locations of key files in the SDK
-BOOTGEN = $(SDK_ROOT)/bin/bootgen
-BINUTILS_DIR = $(SDK_ROOT)/gnu/arm/lin/bin
 # Cross-compilation tuple for toolkit
-CROSS_COMPILE = arm-xilinx-linux-gnueabi-
+COMPILER_PREFIX = arm-xilinx-linux-gnueabi
 
 # The final boot image is assembled here
 BOOT_IMAGE = $(PANDA_ROOT)/boot
@@ -35,8 +33,20 @@ KERNEL_TAG = xilinx-v2015.1
 # Configuration and local settings.
 include CONFIG
 
+
+CROSS_COMPILE = $(COMPILER_PREFIX)-
+
+ifdef SDK_ROOT
+    BOOTGEN ?= $(SDK_ROOT)/bin/bootgen
+    BINUTILS_DIR ?= $(SDK_ROOT)/gnu/arm/lin
+endif
+
+ifdef BINUTILS_DIR
+    SYSROOT ?= $(BINUTILS_DIR)/$(COMPILER_PREFIX)/libc
+endif
+
 # We'll check that these symbols have been defined.
-REQUIRED_SYMBOLS = ROOTFS_TOP SDK_ROOT TAR_FILES PANDA_ROOT
+REQUIRED_SYMBOLS = ROOTFS_TOP BOOTGEN BINUTILS_DIR SYSROOT TAR_FILES PANDA_ROOT
 
 
 default: boot
@@ -54,7 +64,7 @@ BOOT_BUILD = $(BUILD_ROOT)/boot
 
 U_BOOT_TOOLS = $(U_BOOT_BUILD)/tools
 
-export PATH := $(BINUTILS_DIR):$(U_BOOT_TOOLS):$(PATH)
+export PATH := $(BINUTILS_DIR)/bin:$(U_BOOT_TOOLS):$(PATH)
 
 
 # ------------------------------------------------------------------------------
@@ -216,6 +226,7 @@ u-boot-src: $(U_BOOT_SRC)
 
 # Command for building rootfs.  Need to specify both action and target name.
 MAKE_ROOTFS = \
+    $(call EXPORT,COMPILER_PREFIX SYSROOT) \
     $(ROOTFS_TOP)/rootfs -f '$(TAR_FILES)' -r $(PANDA_ROOT) -t $(CURDIR)/$1 $2
 
 %.gz: %

docs/building.rst

@@ -53,6 +53,25 @@ and modify the following fields as required:
     This needs to point to the root directory of the Diamond rootfs builder,
     download from the github location given above.
 
+Three files and directories are taken from ``SDK_ROOT``, and they can instead be
+specified directly.  Note that in this case ``SDK_ROOT`` must *not* be set.
+
+``BOOTGEN``
+    This is the path to a Xilinx toolchain tool used to build the ``boot.bin``
+    file.  By default this is set to ``$(SDK_ROOT)/bin/bootgen``.
+
+``BINUTILS_DIR``
+    This is the path to the gcc cross-compiler toolchain to use.  By default
+    this is set to ``$(SDK_ROOT)/gnu/arm/lin``.  The directory
+    ``$(BINUTILS_DIR)/bin`` will be added to the path during the build.
+
+``SYSROOT``
+    This is the path to the compiled system root (derived from libc).  Normally
+    this is part of the installed toolchain, and if not set elsewhere this is
+    set to ``$(BINUTILS_DIR)/$(COMPILER_PREFIX)/libc``.
+
+Note that the ``COMPILER_PREFIX`` symbol can also be overwritten if required.
+The default value is ``arm-xilinx-linux-gnueabi``.
 
 Sources
 ~~~~~~~

initramfs/CONFIG

@@ -1,8 +1,6 @@
 # Kernel initramfs definition.  This is a minimal image with just enough to do
 # what we need to prepare to run the true system.
 
-TOOLCHAIN = xlnx-zynq
-
 PACKAGES += busybox
 busybox_VERSION = 1.23.2
 busybox_CONFIG = $(configdir)/busybox.config

rootfs/CONFIG

@@ -2,7 +2,6 @@
 
 # -----------------------------------------------------------------------------
 # Package definitions for Zynq
-TOOLCHAIN = xlnx-zynq
 
 PACKAGES += busybox
 busybox_VERSION = 1.23.2