Create separate CMake toolchain file. Add references to toolchain file in each firmware CMakeLists.txt. I suspect this can be simpler still, just not sure how, yet...

firmware/CMakeLists.txt

@@ -21,6 +21,8 @@
 # Top directory CMake project for HackRF firmware
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE toolchain-arm-cortex-m.cmake)
+
 project (hackrf_firmware_all)
 
 add_subdirectory(blinky)

firmware/blinky/CMakeLists.txt

@@ -20,6 +20,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(blinky)
 
 include(../hackrf-common.cmake)

firmware/hackrf-common.cmake

@@ -24,44 +24,8 @@
 
 # derived primarily from Makefiles in libopencm3
 
-cmake_minimum_required(VERSION 2.8.9)
-
 enable_language(C CXX ASM)
 
-include(CMakeForceCompiler)
-
-set(CMAKE_SYSTEM_NAME Generic)
-set(CMAKE_SYSTEM_PROCESSOR cortex-m4)
-
-CMAKE_FORCE_C_COMPILER(arm-none-eabi-gcc GNU)
-CMAKE_FORCE_CXX_COMPILER(arm-none-eabi-g++ GNU)
-
-execute_process(
-  COMMAND ${CMAKE_C_COMPILER} -print-file-name=libc.a
-  OUTPUT_VARIABLE CMAKE_INSTALL_PREFIX
-  OUTPUT_STRIP_TRAILING_WHITESPACE
-)
-get_filename_component(CMAKE_INSTALL_PREFIX
-  "${CMAKE_INSTALL_PREFIX}" PATH
-)
-get_filename_component(CMAKE_INSTALL_PREFIX
-  "${CMAKE_INSTALL_PREFIX}/.." REALPATH
-)
-set(CMAKE_INSTALL_PREFIX  ${CMAKE_INSTALL_PREFIX} CACHE FILEPATH
-    "Install path prefix, prepended onto install directories.")
-
-message(STATUS "Cross-compiling with the gcc-arm-embedded toolchain")
-message(STATUS "Toolchain prefix: ${CMAKE_INSTALL_PREFIX}")
-
-set(CMAKE_ASM_COMPILER ${CMAKE_C_COMPILER})
-#set(CMAKE_LD ${CMAKE_INSTALL_PREFIX}/bin/ld CACHE INTERNAL "ld tool")
-set(CMAKE_OBJCOPY ${CMAKE_INSTALL_PREFIX}/bin/objcopy CACHE INTERNAL "objcopy tool")
-
-set(CMAKE_FIND_ROOT_PATH ${CMAKE_INSTALL_PREFIX})
-set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
-set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
-
 SET(PATH_HACKRF ../..)
 SET(PATH_HACKRF_FIRMWARE ${PATH_HACKRF}/firmware)
 SET(PATH_HACKRF_FIRMWARE_COMMON ${PATH_HACKRF_FIRMWARE}/common)

firmware/hackrf_usb/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(hackrf_usb)
 
 include(../hackrf-common.cmake)

firmware/mixertx/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(mixertx)
 
 include(../hackrf-common.cmake)

firmware/sgpio-rx/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(sgpio-rx)
 
 include(../hackrf-common.cmake)

firmware/sgpio/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(sgpio_test)
 
 include(../hackrf-common.cmake)

firmware/sgpio_passthrough/CMakeLists.txt

@@ -20,6 +20,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(sgpio_passthrough)
 
 include(../hackrf-common.cmake)

firmware/simpletx/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(simpletx)
 
 include(../hackrf-common.cmake)

firmware/spiflash/CMakeLists.txt

@@ -20,6 +20,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(spiflash)
 
 include(../hackrf-common.cmake)

firmware/startup/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(startup)
 
 include(../hackrf-common.cmake)

firmware/startup_systick/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(startup_systick)
 
 include(../hackrf-common.cmake)

firmware/startup_systick_perfo/CMakeLists.txt

@@ -19,6 +19,8 @@
 #
 
 cmake_minimum_required(VERSION 2.8.9)
+set(CMAKE_TOOLCHAIN_FILE ../toolchain-arm-cortex-m.cmake)
+
 project(startup_systick_perfo_SPIFI)
 
 include(../hackrf-common.cmake)

firmware/toolchain-arm-cortex-m.cmake

@@ -0,0 +1,54 @@
+# Copyright 2014 Jared Boone <jared@sharebrained.com>
+#
+# This file is part of HackRF.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; see the file COPYING.  If not, write to
+# the Free Software Foundation, Inc., 51 Franklin Street,
+# Boston, MA 02110-1301, USA.
+#
+
+set(CMAKE_SYSTEM_NAME Generic)
+set(CMAKE_SYSTEM_VERSION 1)
+set(CMAKE_SYSTEM_PROCESSOR arm)
+
+include(CMakeForceCompiler)
+
+CMAKE_FORCE_C_COMPILER(arm-none-eabi-gcc GNU)
+CMAKE_FORCE_CXX_COMPILER(arm-none-eabi-g++ GNU)
+
+execute_process(
+  COMMAND ${CMAKE_C_COMPILER} -print-file-name=libc.a
+  OUTPUT_VARIABLE CMAKE_INSTALL_PREFIX
+  OUTPUT_STRIP_TRAILING_WHITESPACE
+)
+get_filename_component(CMAKE_INSTALL_PREFIX
+  "${CMAKE_INSTALL_PREFIX}" PATH
+)
+get_filename_component(CMAKE_INSTALL_PREFIX
+  "${CMAKE_INSTALL_PREFIX}/.." REALPATH
+)
+set(CMAKE_INSTALL_PREFIX  ${CMAKE_INSTALL_PREFIX} CACHE FILEPATH
+    "Install path prefix, prepended onto install directories.")
+
+message(STATUS "Cross-compiling with the gcc-arm-embedded toolchain")
+message(STATUS "Toolchain prefix: ${CMAKE_INSTALL_PREFIX}")
+
+set(CMAKE_ASM_COMPILER ${CMAKE_C_COMPILER})
+#set(CMAKE_LD ${CMAKE_INSTALL_PREFIX}/bin/ld CACHE INTERNAL "ld tool")
+set(CMAKE_OBJCOPY ${CMAKE_INSTALL_PREFIX}/bin/objcopy CACHE INTERNAL "objcopy tool")
+
+set(CMAKE_FIND_ROOT_PATH ${CMAKE_INSTALL_PREFIX})
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)