Documentation update
This commit is contained in:
Sascha Hauer
parent
631b71e69c
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96f4672d44
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@ -1,107 +0,0 @@
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For long time U-Boot has served as a reliable and versatile bootloader for
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embedded systems, but over the time more and more limitations appeared.
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With U-Boot one hasd to know the memory layout of a particular device to work
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with it. For example to use tftpboot you need to know a memory address where
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you can store the file you are just loading. Saving it in flash requires you
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to know where in the memory space your flash device is and what erase block
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size it has. Configuring U-Boot means that you handle a lot of #defines. This
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usually starts with one define to activate a feature, compiling U-Boot and
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letting the compiler tell you what other defines you'll probably need.
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This is an attempt to rework U-Boot to fit the needs of modern embedded
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systems. Features include:
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- A posix based file API
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inside U-Boot the usual open/close/read/write/lseek functions are used.
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This makes it familiar to everyone who has programmed under unix systems.
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- usual shell commands like ls/cd/mkdir/echo/cat,...
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- The environment is not a variable store anymore, but a file store. It has
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currently some limitations, of course. The environment is not a real
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read/write filesystem, it is more like a tar archive, or even more like
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an ar archive, because it cannot handle directories. The saveenv command
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saves the files under a certain directory (by default /env) in persistent
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storage (by default /dev/env0). There is a counterpart called loadenv, too.
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- Real filesystem support
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The loader starts up with mounting a ramdisk on /. Then a devfs is mounted
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on /dev allowing the user (or shell commands) to access devices. Apart from
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these two filesystems there is currently one filesystem ported: cramfs. One
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can mount it with the usual mount command.
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- device/driver model
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Devices are no longer described by defines in the config file. Instead
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there are devices which can be registered in the board .c file or
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dynamically allocated. Drivers will match upon the devices automatically.
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- clocksource support
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Timekeeping has been simplified by the use of the Linux clocksource API.
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Only one function is needed for a new board, no [gs]et_timer[masked]() or
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reset_timer[masked]() functions.
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- Kconfig and Kernel build system
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Only targets which are really needed get recompiled. Parallel builds are
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no problem anymore. This also removes the need for many many ifdefs in
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the code.
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- simulation target
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U-Boot can be compiled to run under Linux. While this is rather useless
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in real world this is a great debugging and development aid. New features
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can be easily developped and tested on long train journeys and started
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under gdb. There is a console driver for linux which emulates a serial
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device and a tap based ethernet driver. Linux files can be mapped to
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devices under U-Boot to emulate storage devices.
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- device parameter support
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Each device can have a unlimited number of parameters. They can be accessed
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on the command line with <devid>.<param>="...", for example
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'eth0.ip=192.168.0.7' or 'echo $eth0.ip'
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- initcalls
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hooks in the startup process can be archieved with *_initcall() directives
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in each file.
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- getopt
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There is a small getopt implementation. Some commands got really
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complicated (both in code and in usage) due to the fact that U-Boot only
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allowed positional parameters.
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- editor
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Scripts can be edited with a small editor. This editor has no features
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except the ones really needed: moving the cursor and typing characters.
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To get started try
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ARCH=linux make linux_defconfig
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ARCH=linux make menuconfig
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ARCH=linux make
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./vmlinux
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(you can also do a 'ln -s linux cross_arch' to specify ARCH, the Makefile
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will read the link. Same with 'ln -s arm cross_compile', for example)
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This will currently only work on an IA32 architecture, because of some
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hardcoded values in the linker script because and little endian is assumed.
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Starting U-Boot as root will give you a new tap device which you can
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configure with
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ifconfig tap0 172.0.0.1 up
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After setting the network parameters under U-Boot (see 'devinfo eth0') you
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can start with sending a ping request to your host. If you have a tftp
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server running on your host try 'tftpboot <somefile> /target_file'
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For informations on how to map a file to U-Boot try ./vmlinux -h.
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For example if you wish to map a cramfs image to u-boot you can generate one
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with mkcramfs <dir> cramfs.bin and then start U-Boot with -i cramfs.bin. The
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image can be mounted with 'mkdir /cram; mount /dev/fd0 cramfs /cram'
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Still reading?
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Well, of course I only talked about the sunny side of life. This stuff is
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highly experimental. The code has so far only been tested under ARM and
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partly under PowerPC. On PowerPC This loader is not even able to start a
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kernel. Much work has to be done until this becomes a usable bootloader.
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Despite this I believe this _can_ become usable with reasonable effort.
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... to be continued
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@ -33,7 +33,7 @@ with the initial value of the parameter. If the framework handles the set
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function it will try to free the value of the parameter. If this is a
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static array bad things will happen. A parameter can have the flag
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PARAM_FLAG_RO which means that the parameter is readonly. It is perfectly ok
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then to point value to a static array.
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then to point the value to a static array.
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const char *dev_get_param(struct device_d *dev, const char *name);
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@ -46,6 +46,8 @@ static int scb9328_console_init(void)
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return 0;
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}
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console_initcall(scb9328_console_init);
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- For most boards you will have to register a cfi_flash device. NAND flash
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is not ported yet.
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@ -54,8 +56,6 @@ static int scb9328_console_init(void)
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This will add an area starting at 0x40000 of size 0x20000 of the device
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cfi_dev as env0.
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console_initcall(scb9328_console_init);
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- Port missing drivers. Depending on the driver this can a be rather simple
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process:
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@ -68,11 +68,13 @@ console_initcall(scb9328_console_init);
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Ethernet drivers
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- Basically do the same as with serial drivers.
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- Identify the parts of the driver which handle the MAC address. There are
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now two fields in struct eth_device. get_mac_address() shall retrieve the
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MAC address from the EEPROM if one is connected. If you don't have an
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EEPROM just return -1. set_mac_address() shall set the MAC address in
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the device. All magic previously done with getenv/setenv(ethaddr) must be
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removed.
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now two functions handling them in struct eth_device.
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get_mac_address() retrieve the MAC address from the EEPROM if one is
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connected. If you don't have an EEPROM just return -1.
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set_mac_address() set the MAC address in the device. All magic previously
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done with getenv/setenv(ethaddr) must be removed.
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During startup U-Boot calls get_mac_address() to see if an EEPROM is
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connected. If so, it calls set_mac_address() with this address. This
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is done even if networking is not used during startup. This makes sure
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@ -118,4 +120,4 @@ calc_source:
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addresses in the objdump without doing offset calculation.
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- On arm most of the duplicate code under cpu/arm* is already merged into
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arch/arm/cpu. the start.S files are missing though.
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arch/arm/cpu. The start.S files are missing though.
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155
README.u2
155
README.u2
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@ -7,8 +7,69 @@ today's embedded systems, seen from a user's point of view.
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Nevertheless, there are quite some design flaws which turned out over
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the last years and we think that they cannot be solved in a production
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tree. So this tree tries to do several things right - without caring
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about losing support for old boards. So if you aim at stability at this
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time, stay with the official U-Boot releases.
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about losing support for old boards.
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General features include:
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- A posix based file API
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inside U-Boot the usual open/close/read/write/lseek functions are used.
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This makes it familiar to everyone who has programmed under unix systems.
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- usual shell commands like ls/cd/mkdir/echo/cat,...
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- The environment is not a variable store anymore, but a file store. It has
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currently some limitations, of course. The environment is not a real
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read/write filesystem, it is more like a tar archive, or even more like
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an ar archive, because it cannot handle directories. The saveenv command
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saves the files under a certain directory (by default /env) in persistent
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storage (by default /dev/env0). There is a counterpart called loadenv, too.
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- Real filesystem support
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The loader starts up with mounting a ramdisk on /. Then a devfs is mounted
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on /dev allowing the user (or shell commands) to access devices. Apart from
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these two filesystems there is currently one filesystem ported: cramfs. One
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can mount it with the usual mount command.
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- device/driver model
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Devices are no longer described by defines in the config file. Instead
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there are devices which can be registered in the board .c file or
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dynamically allocated. Drivers will match upon the devices automatically.
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- clocksource support
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Timekeeping has been simplified by the use of the Linux clocksource API.
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Only one function is needed for a new board, no [gs]et_timer[masked]() or
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reset_timer[masked]() functions.
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- Kconfig and Kernel build system
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Only targets which are really needed get recompiled. Parallel builds are
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no problem anymore. This also removes the need for many many ifdefs in
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the code.
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- simulation target
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U-Boot can be compiled to run under Linux. While this is rather useless
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in real world this is a great debugging and development aid. New features
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can be easily developped and tested on long train journeys and started
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under gdb. There is a console driver for linux which emulates a serial
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device and a tap based ethernet driver. Linux files can be mapped to
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devices under U-Boot to emulate storage devices.
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- device parameter support
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Each device can have a unlimited number of parameters. They can be accessed
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on the command line with <devid>.<param>="...", for example
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'eth0.ip=192.168.0.7' or 'echo $eth0.ip'
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- initcalls
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hooks in the startup process can be archieved with *_initcall() directives
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in each file.
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- getopt
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There is a small getopt implementation. Some commands got really
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complicated (both in code and in usage) due to the fact that U-Boot only
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allowed positional parameters.
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- editor
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Scripts can be edited with a small editor. This editor has no features
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except the ones really needed: moving the cursor and typing characters.
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Building U-Boot
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@ -22,7 +83,8 @@ kernel.
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For the examples below, we use the User Mode U-Boot implementation, which
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is a port of U-Boot to the Linux userspace. This makes it possible to
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test drive the code without having real hardware. So for this test
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scenario, ARCH=linux is the valid architecture selection.
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scenario, ARCH=linux is the valid architecture selection. This currently
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only works on ia32 hosts and partly on x86-64.
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Selection of the architecture and the cross compiler can be done in two
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ways. You can either specify it using the environment variables ARCH
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@ -57,7 +119,7 @@ U-Boot usually needs an environment for storing the configuation data.
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You can generate an environment using the example environment contained
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in examples/environment:
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# ./scripts/ubootenv -s examples/environment/ env.bin
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# ./scripts/ubootenv -s -p 0x10000 examples/environment/ env.bin
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To get some files to play with you can generate a cramfs image:
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# mkcramfs somedir/ cramfs.bin
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@ -80,61 +142,60 @@ load it to /env. It then executes /env/init if it exists. If you have
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loaded the example environment U-Boot will show you a menu asking for
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your settings.
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If you have started U-Boot as root you will find a new tap device on your
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host which you can configure using ifconfig. Once you configured U-Boots
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network settings accordingly you can do a ping or tftpboot.
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If you have mapped a cramfs image try mounting it with
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FIXME: cfi currently doesn't work with um-uboot
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# mkdir /cram
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# mount /dev/fd0 cramfs /cram
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Memory can be examined as usual using md/mw commands. They both understand
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the -f <file> option to tell the commands that they should work on the
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specified files instead of /dev/mem which holds the complete address space.
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Note that if you call 'md /dev/fd0' (without -f) U-Boot will segfault on
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the host, because it will interpret /dev/fd0 as a number.
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Commands
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--------
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Directory layout
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----------------
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devinfo
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addpart
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pwd
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cd
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ls
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cat
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tftpboot <dest> <source> FIXME: order?
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tftpboot /dev/nor0.1 <source>
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erase -f /dev/nor0.1
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help
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edit -> ctrl-c ctrl-d
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md -f /dev/nor0.1
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exec /env/init FIXME: doesn't work yet
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saveenv (makes /env persistent) -> /dev/env0
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printenv
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mount
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Most of the directory layout is based upon the Linux Kernel:
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Shell
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-----
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arch/*/ -> contains architecture specific parts
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arch/*/mach-*/ -> SoC specific code
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- doesn't have switch/case yet
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- only one variable space
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[ ] add variable space
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drivers/serial -> drivers
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drivers/net
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drivers/...
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Drivers
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-------
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include/asm-* -> architecture specific includes
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include/asm-*/arch-* -> SoC specific includes
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/dev
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serial
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partition
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environment -> /env; /env/init
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fs/ -> filesystem support and filesystem drivers
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Design
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------
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lib/ -> generic library functions (getopt, readline and the
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like)
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include/driver.h
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board/scb9328.c
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include/param.h: each device can have parameters; can be changed on
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runtime; get/set can be overwritten by implementation.
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common/ -> common stuff
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- xfunctions: do panic if error
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- proposed design:
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arch/
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arch/arm/cpu-arm920t/
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arch/arm/board-.../
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board/ is obsolete
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commands/ -> many things previously in common/cmd_*, one command
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per file
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- arch/*/Makefile is central makefile
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net/ -> Networking stuff
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scripts/ -> Kconfig system
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Documentation/ ->
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There is still the old directory layout in the tree which of course should be
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merged in one way or the other:
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lib_*/ -> currently unused
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cpu/* -> currently unsused
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post/ -> untouched
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nand_spl/ -> untouched
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dtt/ -> untouched
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disk/ -> untouched
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documentation/ -> untouched
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