199.htm

pcb设计资料初学者难得的入门资料包含工厂制作过程

InterruptControllerGetPendingIntVector(&intvector); <br>
InterruptControllerGetPendingIntSrc((&irq); <br>
action = (struct irqaction *)intvector; <br>
if ( action == NULL ) { <br>
   printk(*No handler for hw0 irq: %i\n*, irq); <br>
return; <br>
} <br>
hardirq_enter(cpu); <br>
action->handler(irq, action->dev_id, regs); <br>
kstat.irqs[0][irq]++; <br>
hardirq_exit(cpu); <br>
} // InterruptController_InterruptHandler () <br>
The functions request_irq(), free_irq(), enable_irq() and disable_irq() have <br>
 to be implemented for your target platform. request_irq() is used to instal <br>
l an interrupt handler for a given interrupt source. free_irq() needs to fre <br>
e the memory allocated for the given interrupt. enable_irq() needs to make a <br>
 call to the interrupt controller function that enables the given interrupt <br>
line and disable_irq() needs to disable the given interrupt line. <br>
Timer interrupt <br>
File $(TOPDIR)/arch/MY_ARCH/MY_PLATFORM/time.c contains the platform-depende <br>
nt timer code. The Linux kernel on MIPS requires a 100Hz timer interrupt. In <br>
 the MIPS, one of the timers in coprocessor 0 is programmed to generate 100H <br>

z interrupts. The count register and the compare register together make up t <br>
he timer. When active, the count register contains a free running counter. O <br>
n each processor clock-tick, the value in the register increments by one. Th <br>
e register is reset and an external hardware interrupt is generated when the <br>
 values in the count register and compare register match. After the count re <br>
gister is reset, it restarts to count on the next processor clock-tick. The <br>
timer interrupt service routine (ISR) needs to call the do_timer() routine. <br>
Performing a write to the compare register clears the timer interrupt. <br>
Serial console driver <br>
The console runs on top of a serial driver. A polled serial driver can be us <br>
ed for printk() (kernel debug message) functionality. The minimum functions <br>
that this driver needs to provide are the following: <br>
serial_console_init()-for registering the console printing procedure for ker <br>
nel printk() functionality, before the console driver is properly initialize <br>
d <br>
serial_console_setup()-for initializing the serial port <br>
serial_console_write(struct console *console, const char *string, int count) <br>
-for writing "count" characters <br>
Hook up the serial port on your development board to your host development p <br>
latform, then start up a serial communication program on your host developme <br>
nt platform to communicate with your target. <br>
tty driver <br>
tty driver <br>
An interrupt driven serial driver can be used to create a terminal device. A <br>
 terminal device can be created by registering the serial driver with tty. A <br>
 variety of serial drivers are available in the $(TOPDIR)/drivers/char direc <br>
tory. The driver that matches closest to the serial port hardware being used <br>
 should be picked up and modified. The interfaces to an interrupt-driven cha <br>
racter driver under Linux have been explained in Linux Device Drivers by Rub <br>
ini (see References). <br>
CONFIG_SERIAL (serial support) has to be defined as Y in "make config." To t <br>
est, hook up the interrupt-driven serial port to the host development platfo <br>
rm and run a serial communication program to communicate with your target (t <br>
erminal device). <br>
Bootloader <br>
Although LILO (the Linux loader) should be available for your architecture, <br>
it may be quicker to use your own bootloader to load the Linux kernel. [4] L <br>
ILO passes some information to the kernel in a way similar to how an Intel P <br>
C BIOS passes information to the kernel. LILO then calls the "kernel_entry" <br>
function inside the kernel, giving up control to the kernel. If you're using <br>
 your own bootloader, you need to pass parameters to the kernel by adding th <br>
em to the "command_line" string, which is parsed by the kernel. In my case, <br>
I had to add "root=/dev/ram" to the command_line string to tell the kernel t <br>
hat I wanted the ramdisk to be mounted as the root file system. You could ad <br>
d other kernel parameters to this string, if needed. Load the image at the s <br>

pecified load address using your bootloader. Start executing from the addres <br>
s of the "kernel_entry" symbol in the kernel image. <br>
It will be easier to debug if the bootloader had its own "print" function, b <br>
ecause the printk function inside the kernel buffers all the output to the c <br>
onsole until the console is initialized (console_init() in $(TOPDIR)/init/ma <br>
in.c). <br>
If everything goes well, you should get something like the following message <br>
 on your kernel debug terminal: <br>
Detected 32MB of memory. <br>
Loading R4000/MIPS32 MMU routines. <br>
CPU revision is: 000028a0 <br>
Primary instruction cache 32 kb, linesize 32 bytes <br>
Primary data cache 32 kb, linesize 32 bytes <br>
Linux version 2.2.12 (rpalani@rplinux) <br>
(gcc version egcs-2.90.29 980515 (egcs-10)) <br>
CPU frequency 200.00 MHz <br>
Calibrating delay loop: 199.88 BogoMIPS <br>
Memory: 14612k/16380k available <br>
(472k kernel code, 908k data) <br>
Checking for 鍂ait' instruction...  available. <br>
POSIX conformance testing by UNIFIX <br>
Linux NET4.0 for Linux 2.2 <br>

Based upon Swansea University Computer Society NET3.039 <br>
Starting kswapd v1.1.1.1 <br>
No keyboard driver installed <br>
RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize <br>
RAMDISK: Compressed image found at block 0 <br>
VFS: Mounted root (ext2 filesystem) readonly. <br>
Freeing unused kernel memory: 32k freed <br>
The kernel tries to open a console and find and execute "init" from one of t <br>
he following places in the root file system, in sequence: /sbin/init, /etc/i <br>
nit, /bin/init. If all the above fail, it tries to create an interactive she <br>
ll (/bin/sh as happens in my case). If even this fails, then the kernel "pan <br>
ics," as would you. I hope that this does not happen in your case. If it doe <br>
sn't a shell prompt will appear on the console. Applications can be run on t <br>
he system by dropping them inside the ramdisk image and executing from there <br>
. <br>
Adding new drivers <br>
New drivers for your target hardware can be added by picking up the driver t <br>
hat matches most closely to your hardware (a vast number are available) and <br>
modifying it. If you are dealing with a proprietary piece of hardware that i <br>
s specific to your system, use the standard driver interfaces to implement a <br>
 driver for the same. These drivers can be implemented as kernel modules in <br>
order to load and unload them using insmod and rmmod. <br>

Useful tips <br>
Sprinkle printk() statements liberally throughout your code to aid debugging <br>
. This may be an obvious suggestion, but it is worth mentioning. Remote GDB <br>
[5] may also be useful for debugging, though in my experience printk's are m <br>
ore than enough for debugging kernel code. In remote GDB, the host developme <br>
nt system runs gdb and talks to the kernel running on the target platform vi <br>
a a serial line. You need to setup CONFIG_REMOTE_DEBUG = Y in the kernel con <br>
figuration. putDebugChar(char ch) and getDebugChar() are the two functions t <br>
hat need to be implemented over the serial port for remote debugging using g <br>
db. <br>
If you are forced to use a common port for console and debug, the GDB output <br>
 can be multiplexed with the debug output by setting the high bit in putDebu <br>
gChar(). GDB forwards output without the high bit set to the user session. <br>
To start with, implement only the basic minimum functions for the tty driver <br>
 as specified in $(TOPDIR)/include/linux/tty_ldisc.h. <br>
Real-time requirements <br>
The subject of embedded systems is not complete without a mention of real-ti <br>
me requirements. The standard Linux kernel provides soft real-time support. <br>
There are currently two major approaches to achieve hard real-time with Linu <br>
x. These are RTLinux and RTAI. Both approaches have their own real-time kern <br>
el running Linux as the lowest priority task. When dealing with proprietary <br>
hardware, as it often happens in embedded systems, the issue of proprietary <br>

software crops up as well. In Linux, proprietary modules can be handled with <br>
 the GNU Lesser General Public License, which permits linking with non-free <br>
modules. It is compatible with the GNU General Public License, which is a fr <br>
ee software license, and a copyleft license. [6] <br>
With a good knowledge of the processor architecture and the hardware devices <br>
 being used, porting Linux to an embedded system can be accomplished in a sh <br>
ort time frame, which is of vital importance in the fast paced embedded syst <br>
ems market. In my case, where I have been using UNIX for quite some time, it <br>
 took me around two months to complete the port of the minimum kernel functi <br>
onality to our platform. Porting Linux to a different platform should not ta <br>
ke that long when doing it for a second time. <br>
Rajesh Palani works as a senior software engineer at Philips Semiconductors. <br>
 He has been designing and developing embedded software since 1993. He has w <br>
orked on the design and development of software (ranging from firmware to ap <br>
plications) for set-top boxes, digital still cameras, TVs (Teletext), and an <br>
tilock braking systems. Contact him at [e-mail]. <br>
Endnotes <br>
1. Stands for "GNU's Not Unix," a project launched in 1984 to develop a comp <br>
lete Unix-like operating system which is free software: the GNU system. <br>
Back <br>
2. The topmost directory in the Linux source tree (/usr/src/linux, by defaul <br>
t). <br>
t). <br>
Back <br>
3. Translation Lookaside Buffer-hardware used for virtual to physical addres <br>
s mapping in a processor. <br>
Back <br>
4. The subject of developing a bootloader for your processor is outside the <br>
scope of this article. <br>
Back <br>
5. GNU Debugger-helps you to start your program, make it stop on specified c <br>
onditions, examine what has happened (when your program has stopped), and ch <br>
ange things in your program. <br>
Back <br>
6. Copyleft says that anyone who redistributes the software, with or without <br>
 changes, must pass along the freedom to further copy and change it. <br>
Back <br>
References <br>
A Web site containing a wealth of information on Linux in general: <br>
www.kernel.org/LDP <br>
Web sites devoted to Linux on MIPS: <br>
www.paralogos.com/mipslinux <br>
www.linux-vr.org <br>
www.linux.sgi.com <br>
Web sites dealing with real-time Linux: <br>

www.rtlinux.org <br>
www.rtai.org <br>
Beck, M. et al. Linux Kernel Internals. New York: Addison-Wesley, 1998. This <br>
 book is a good source of information on the kernel internals. Rubini, Alesa <br>
ndro. Linux Device Drivers. Sebastopol, CA: O Reilly & Associates, 1998. Thi <br>
s book delves into kernel internals and talks in detail about all types of d <br>
evice drivers under Linux. <br>
  <br>
【 在 dross (走人了) 的大作中提到: 】 <br>
: 如果目标板不是使用i386结构的话呢 <br>
  <br>
  <br>
-- <br>
  人有时候需要一点点刺激 <br>
  人有时候需要一点点打击 <br>
  在那时侯不知道生命的意义就在超越自己 <br>
  争取一种意义非凡的胜利 <br>
  我们都是和自己赛跑的人 <br>
  为了更好的明天拼命努力 <br>
  <br>
  <br>
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