arm.rst (7903B)
1======================= 2ARM Linux 2.6 and upper 3======================= 4 5 Please check <ftp://ftp.arm.linux.org.uk/pub/armlinux> for 6 updates. 7 8Compilation of kernel 9--------------------- 10 11 In order to compile ARM Linux, you will need a compiler capable of 12 generating ARM ELF code with GNU extensions. GCC 3.3 is known to be 13 a good compiler. Fortunately, you needn't guess. The kernel will report 14 an error if your compiler is a recognized offender. 15 16 To build ARM Linux natively, you shouldn't have to alter the ARCH = line 17 in the top level Makefile. However, if you don't have the ARM Linux ELF 18 tools installed as default, then you should change the CROSS_COMPILE 19 line as detailed below. 20 21 If you wish to cross-compile, then alter the following lines in the top 22 level make file:: 23 24 ARCH = <whatever> 25 26 with:: 27 28 ARCH = arm 29 30 and:: 31 32 CROSS_COMPILE= 33 34 to:: 35 36 CROSS_COMPILE=<your-path-to-your-compiler-without-gcc> 37 38 eg.:: 39 40 CROSS_COMPILE=arm-linux- 41 42 Do a 'make config', followed by 'make Image' to build the kernel 43 (arch/arm/boot/Image). A compressed image can be built by doing a 44 'make zImage' instead of 'make Image'. 45 46 47Bug reports etc 48--------------- 49 50 Please send patches to the patch system. For more information, see 51 http://www.arm.linux.org.uk/developer/patches/info.php Always include some 52 explanation as to what the patch does and why it is needed. 53 54 Bug reports should be sent to linux-arm-kernel@lists.arm.linux.org.uk, 55 or submitted through the web form at 56 http://www.arm.linux.org.uk/developer/ 57 58 When sending bug reports, please ensure that they contain all relevant 59 information, eg. the kernel messages that were printed before/during 60 the problem, what you were doing, etc. 61 62 63Include files 64------------- 65 66 Several new include directories have been created under include/asm-arm, 67 which are there to reduce the clutter in the top-level directory. These 68 directories, and their purpose is listed below: 69 70 ============= ========================================================== 71 `arch-*` machine/platform specific header files 72 `hardware` driver-internal ARM specific data structures/definitions 73 `mach` descriptions of generic ARM to specific machine interfaces 74 `proc-*` processor dependent header files (currently only two 75 categories) 76 ============= ========================================================== 77 78 79Machine/Platform support 80------------------------ 81 82 The ARM tree contains support for a lot of different machine types. To 83 continue supporting these differences, it has become necessary to split 84 machine-specific parts by directory. For this, the machine category is 85 used to select which directories and files get included (we will use 86 $(MACHINE) to refer to the category) 87 88 To this end, we now have arch/arm/mach-$(MACHINE) directories which are 89 designed to house the non-driver files for a particular machine (eg, PCI, 90 memory management, architecture definitions etc). For all future 91 machines, there should be a corresponding arch/arm/mach-$(MACHINE)/include/mach 92 directory. 93 94 95Modules 96------- 97 98 Although modularisation is supported (and required for the FP emulator), 99 each module on an ARM2/ARM250/ARM3 machine when is loaded will take 100 memory up to the next 32k boundary due to the size of the pages. 101 Therefore, is modularisation on these machines really worth it? 102 103 However, ARM6 and up machines allow modules to take multiples of 4k, and 104 as such Acorn RiscPCs and other architectures using these processors can 105 make good use of modularisation. 106 107 108ADFS Image files 109---------------- 110 111 You can access image files on your ADFS partitions by mounting the ADFS 112 partition, and then using the loopback device driver. You must have 113 losetup installed. 114 115 Please note that the PCEmulator DOS partitions have a partition table at 116 the start, and as such, you will have to give '-o offset' to losetup. 117 118 119Request to developers 120--------------------- 121 122 When writing device drivers which include a separate assembler file, please 123 include it in with the C file, and not the arch/arm/lib directory. This 124 allows the driver to be compiled as a loadable module without requiring 125 half the code to be compiled into the kernel image. 126 127 In general, try to avoid using assembler unless it is really necessary. It 128 makes drivers far less easy to port to other hardware. 129 130 131ST506 hard drives 132----------------- 133 134 The ST506 hard drive controllers seem to be working fine (if a little 135 slowly). At the moment they will only work off the controllers on an 136 A4x0's motherboard, but for it to work off a Podule just requires 137 someone with a podule to add the addresses for the IRQ mask and the 138 HDC base to the source. 139 140 As of 31/3/96 it works with two drives (you should get the ADFS 141 `*configure` harddrive set to 2). I've got an internal 20MB and a great 142 big external 5.25" FH 64MB drive (who could ever want more :-) ). 143 144 I've just got 240K/s off it (a dd with bs=128k); thats about half of what 145 RiscOS gets; but it's a heck of a lot better than the 50K/s I was getting 146 last week :-) 147 148 Known bug: Drive data errors can cause a hang; including cases where 149 the controller has fixed the error using ECC. (Possibly ONLY 150 in that case...hmm). 151 152 1531772 Floppy 154----------- 155 This also seems to work OK, but hasn't been stressed much lately. It 156 hasn't got any code for disc change detection in there at the moment which 157 could be a bit of a problem! Suggestions on the correct way to do this 158 are welcome. 159 160 161`CONFIG_MACH_` and `CONFIG_ARCH_` 162--------------------------------- 163 A change was made in 2003 to the macro names for new machines. 164 Historically, `CONFIG_ARCH_` was used for the bonafide architecture, 165 e.g. SA1100, as well as implementations of the architecture, 166 e.g. Assabet. It was decided to change the implementation macros 167 to read `CONFIG_MACH_` for clarity. Moreover, a retroactive fixup has 168 not been made because it would complicate patching. 169 170 Previous registrations may be found online. 171 172 <http://www.arm.linux.org.uk/developer/machines/> 173 174Kernel entry (head.S) 175--------------------- 176 The initial entry into the kernel is via head.S, which uses machine 177 independent code. The machine is selected by the value of 'r1' on 178 entry, which must be kept unique. 179 180 Due to the large number of machines which the ARM port of Linux provides 181 for, we have a method to manage this which ensures that we don't end up 182 duplicating large amounts of code. 183 184 We group machine (or platform) support code into machine classes. A 185 class typically based around one or more system on a chip devices, and 186 acts as a natural container around the actual implementations. These 187 classes are given directories - arch/arm/mach-<class> - which contain 188 the source files and include/mach/ to support the machine class. 189 190 For example, the SA1100 class is based upon the SA1100 and SA1110 SoC 191 devices, and contains the code to support the way the on-board and off- 192 board devices are used, or the device is setup, and provides that 193 machine specific "personality." 194 195 For platforms that support device tree (DT), the machine selection is 196 controlled at runtime by passing the device tree blob to the kernel. At 197 compile-time, support for the machine type must be selected. This allows for 198 a single multiplatform kernel build to be used for several machine types. 199 200 For platforms that do not use device tree, this machine selection is 201 controlled by the machine type ID, which acts both as a run-time and a 202 compile-time code selection method. You can register a new machine via the 203 web site at: 204 205 <http://www.arm.linux.org.uk/developer/machines/> 206 207 Note: Please do not register a machine type for DT-only platforms. If your 208 platform is DT-only, you do not need a registered machine type. 209 210--- 211 212Russell King (15/03/2004)