xref: /openbmc/u-boot/doc/README.POST (revision 66fd3d1c)

Power-On-Self-Test support in U-Boot
------------------------------------

This project is to support Power-On-Self-Test (POST) in U-Boot.

1. High-level requirements

The key rquirements for this project are as follows:

1) The project shall develop a flexible framework for implementing
   and running Power-On-Self-Test in U-Boot. This framework shall
   possess the following features:

   o) Extensibility

      The framework shall allow adding/removing/replacing POST tests.
      Also, standalone POST tests shall be supported.

   o) Configurability

      The framework shall allow run-time configuration of the lists
      of tests running on normal/power-fail booting.

   o) Controllability

      The framework shall support manual running of the POST tests.

2) The results of tests shall be saved so that it will be possible to
   retrieve them from Linux.

3) The following POST tests shall be developed for MPC823E-based
   boards:

   o) CPU test
   o) Cache test
   o) Memory test
   o) Ethernet test
   o) Serial channels test
   o) Watchdog timer test
   o) RTC test
   o) I2C test
   o) SPI test
   o) USB test

4) The LWMON board shall be used for reference.

2. Design

This section details the key points of the design for the project.
The whole project can be divided into two independent tasks:
enhancing U-Boot/Linux to provide a common framework for running POST
tests and developing such tests for particular hardware.

2.1. Hardware-independent POST layer

A new optional module will be added to U-Boot, which will run POST
tests and collect their results at boot time. Also, U-Boot will
support running POST tests manually at any time by executing a
special command from the system console.

The list of available POST tests will be configured at U-Boot build
time. The POST layer will allow the developer to add any custom POST
tests. All POST tests will be divided into the following groups:

  1) Tests running on power-on booting only

     This group will contain those tests that run only once on
     power-on reset (e.g. watchdog test)

  2) Tests running on normal booting only

     This group will contain those tests that do not take much
     time and can be run on the regular basis (e.g. CPU test)

  3) Tests running on power-fail booting only

     This group will contain POST tests that consume much time
     and cannot be run regularly (e.g. I2C test)

  4) Manually executed tests

     This group will contain those tests that can be run manually.

If necessary, some tests may belong to several groups simultaneously.
For example, SDRAM test may run on both noarmal and power-fail
booting. On normal booting, SDRAM test may perform a fast superficial
memory test only, while running on power-fail booting it may perform
a full memory check-up.

Also, all tests will be discriminated by the moment they run at.
Specifically, the following groups will be singled out:

  1) Tests running before relocating to RAM

     These tests will run immediatelly after initializing RAM
     as to enable modifying it without taking care of its
     contents. Basically, this group will contain memory tests
     only.

  2) Tests running after relocating to RAM

     These tests will run immediately before entering the main
     loop as to guarantee full hardware initialization.

The POST layer will also distinguish a special group of tests that
may cause system rebooting (e.g. watchdog test). For such tests, the
layer will automatically detect rebooting and will notify the test
about it.

2.1.1. POST layer interfaces

This section details the interfaces between the POST layer and the
rest of U-Boot.

The following flags will be defined:

#define POST_ROM		0x01	/* test runs in ROM */
#define POST_RAM		0x02	/* test runs in RAM */
#define POST_POWERON		0x04	/* test runs on power-on booting */
#define POST_NORMAL		0x08	/* test runs on normal booting */
#define POST_SHUTDOWN		0x10	/* test runs on power-fail booting */
#define POST_MANUAL		0x20	/* test can be executed manually */
#define POST_REBOOT		0x80	/* test may cause rebooting */

The POST layer will export the following interface routines:

  o) int post_run(bd_t *bd, char *name, int flags);

     This routine will run the test (or the group of tests) specified
     by the name and flag arguments. More specifically, if the name
     argument is not NULL, the test with this name will be performed,
     otherwise all tests running in ROM/RAM (depending on the flag
     argument) will be executed. This routine will be called at least
     twice with name set to NULL, once from board_init_f() and once
     from board_init_r(). The flags argument will also specify the
     mode the test is executed in (power-on, normal, power-fail,
     manual).

  o) void post_reloc(ulong offset);

     This routine will be called from board_init_r() and will
     relocate the POST test table.

  o) int post_info(char *name);

     This routine will print the list of all POST tests that can be
     executed manually if name is NULL, and the description of a
     particular test if name is not NULL.

  o) int post_log(char *format, ...);

     This routine will be called from POST tests to log their
     results. Basically, this routine will print the results to
     stderr. The format of the arguments and the return value
     will be identical to the printf() routine.

Also, the following board-specific routines will be called from the
U-Boot common code:

  o) int board_power_mode(void)

     This routine will return the mode the system is running in
     (POST_POWERON, POST_NORMAL or POST_SHUTDOWN).

  o) void board_poweroff(void)

     This routine will turn off the power supply of the board. It
     will be called on power-fail booting after running all POST
     tests.

The list of available POST tests be kept in the post_tests array
filled at U-Boot build time. The format of entry in this array will
be as follows:

struct post_test {
    char *name;
    char *cmd;
    char *desc;
    int flags;
    int (*test)(bd_t *bd, int flags);
};

  o) name

     This field will contain a short name of the test, which will be
     used in logs and on listing POST tests (e.g. CPU test).

  o) cmd

     This field will keep a name for identifying the test on manual
     testing (e.g. cpu). For more information, refer to section
     "Command line interface".

  o) desc

     This field will contain a detailed description of the test,
     which will be printed on user request. For more information, see
     section "Command line interface".

  o) flags

     This field will contain a combination of the bit flags described
     above, which will specify the mode the test is running in
     (power-on, normal, power-fail or manual mode), the moment it
     should be run at (before or after relocating to RAM), whether it
     can cause system rebooting or not.

  o) test

     This field will contain a pointer to the routine that will
     perform the test, which will take 2 arguments. The first
     argument will be a pointer to the board info structure, while
     the second will be a combination of bit flags specifying the
     mode the test is running in (POST_POWERON, POST_NORMAL,
     POST_POWERFAIL, POST_MANUAL) and whether the last execution of
     the test caused system rebooting (POST_REBOOT). The routine will
     return 0 on successful execution of the test, and 1 if the test
     failed.

The lists of the POST tests that should be run at power-on/normal/
power-fail booting will be kept in the environment. Namely, the
following environment variables will be used: post_poweron,
powet_normal, post_shutdown.

2.1.2. Test results

The results of tests will be collected by the POST layer. The POST
log will have the following format:

...
--------------------------------------------
START <name>
<test-specific output>
[PASSED|FAILED]
--------------------------------------------
...

Basically, the results of tests will be printed to stderr. This
feature may be enhanced in future to spool the log to a serial line,
save it in non-volatile RAM (NVRAM), transfer it to a dedicated
storage server and etc.

2.1.3. Integration issues

All POST-related code will be #ifdef'ed with the CONFIG_POST macro.
This macro will be defined in the config_<board>.h file for those
boards that need POST. The CONFIG_POST macro will contain the list of
POST tests for the board. The macro will have the format of array
composed of post_test structures:

#define CONFIG_POST \
	{
		"On-board peripherals test", "board", \
		"  This test performs full check-up of the " \
		"on-board hardware.", \
		POST_RAM | POST_POWERFAIL, \
		&board_post_test \
	}

A new file, post.h, will be created in the include/ directory. This
file will contain common POST declarations and will define a set of
macros that will be reused for defining CONFIG_POST. As an example,
the following macro may be defined:

#define POST_CACHE \
	{
		"Cache test", "cache", \
		"  This test verifies the CPU cache operation.", \
		POST_RAM | POST_NORMAL, \
		&cache_post_test \
	}

A new subdirectory will be created in the U-Boot root directory. It
will contain the source code of the POST layer and most of POST
tests. Each POST test in this directory will be placed into a
separate file (it will be needed for building standalone tests). Some
POST tests (mainly those for testing peripheral devices) will be
located in the source files of the drivers for those devices. This
way will be used only if the test subtantially uses the driver.

2.1.4. Standalone tests

The POST framework will allow to develop and run standalone tests. A
user-space library will be developed to provide the POST interface
functions to standalone tests.

2.1.5. Command line interface

A new command, diag, will be added to U-Boot. This command will be
used for listing all available hardware tests, getting detailed
descriptions of them and running these tests.

More specifically, being run without any arguments, this command will
print the list of all available hardware tests:

=> diag
Available hardware tests:
  cache             - cache test
  cpu               - CPU test
  enet              - SCC/FCC ethernet test
Use 'diag [<test1> [<test2>]] ... ' to get more info.
Use 'diag run [<test1> [<test2>]] ... ' to run tests.
=>

If the first argument to the diag command is not 'run', detailed
descriptions of the specified tests will be printed:

=> diag cpu cache
cpu - CPU test
  This test verifies the arithmetic logic unit of CPU.
cache - cache test
  This test verifies the CPU cache operation.
=>

If the first argument to diag is 'run', the specified tests will be
executed. If no tests are specified, all available tests will be
executed.

It will be prohibited to execute tests running in ROM manually. The
'diag' command will not display such tests and/or run them.

2.1.6. Power failure handling

The Linux kernel will be modified to detect power failures and
automatically reboot the system in such cases. It will be assumed
that the power failure causes a system interrupt.

To perform correct system shutdown, the kernel will register a
handler of the power-fail IRQ on booting. Being called, the handler
will run /sbin/reboot using the call_usermodehelper() routine.
/sbin/reboot will automatically bring the system down in a secure
way. This feature will be configured in/out from the kernel
configuration file.

The POST layer of U-Boot will check whether the system runs in
power-fail mode. If it does, the system will be powered off after
executing all hardware tests.

2.1.7. Hazardous tests

Some tests may cause system rebooting during their execution. For
some tests, this will indicate a failure, while for the Watchdog
test, this means successful operation of the timer.

In order to support such tests, the following scheme will be
implemented. All the tests that may cause system rebooting will have
the POST_REBOOT bit flag set in the flag field of the correspondent
post_test structure. Before starting tests marked with this bit flag,
the POST layer will store an identification number of the test in a
location in IMMR. On booting, the POST layer will check the value of
this variable and if it is set will skip over the tests preceding the
failed one. On second execution of the failed test, the POST_REBOOT
bit flag will be set in the flag argument to the test routine. This
will allow to detect system rebooting on the previous iteration. For
example, the watchdog timer test may have the following
declaration/body:

...
#define POST_WATCHDOG \
	{
		"Watchdog timer test", "watchdog", \
		"  This test checks the watchdog timer.", \
		POST_RAM | POST_POWERON | POST_REBOOT, \
		&watchdog_post_test \
	}
...

...
int watchdog_post_test(bd_t *bd, int flags)
{
	unsigned long start_time;

	if (flags & POST_REBOOT) {
		/* Test passed */
		return 0;
	} else {
		/* disable interrupts */
		disable_interrupts();
		/* 10-second delay */
		...
		/* if we've reached this, the watchdog timer does not work */
		enable_interrupts();
		return 1;
	}
}
...

2.2. Hardware-specific details

This project will also develop a set of POST tests for MPC8xx- based
systems. This section provides technical details of how it will be
done.

2.2.1. Generic PPC tests

The following generic POST tests will be developed:

  o) CPU test

     This test will check the arithmetic logic unit (ALU) of CPU. The
     test will take several milliseconds and will run on normal
     booting.

  o) Cache test

     This test will verify the CPU cache (L1 cache). The test will
     run on normal booting.

  o) Memory test

     This test will examine RAM and check it for errors. The test
     will always run on booting. On normal booting, only a limited
     amount of RAM will be checked. On power-fail booting a fool
     memory check-up will be performed.

2.2.1.1. CPU test

This test will verify the following ALU instructions:

  o) Condition register istructions

     This group will contain: mtcrf, mfcr, mcrxr, crand, crandc,
     cror, crorc, crxor, crnand, crnor, creqv, mcrf.

     The mtcrf/mfcr instructions will be tested by loading different
     values into the condition register (mtcrf), moving its value to
     a general-purpose register (mfcr) and comparing this value with
     the expected one. The mcrxr instruction will be tested by
     loading a fixed value into the XER register (mtspr), moving XER
     value to the condition register (mcrxr), moving it to a
     general-purpose register (mfcr) and comparing the value of this
     register with the expected one. The rest of instructions will be
     tested by loading a fixed value into the condition register
     (mtcrf), executing each instruction several times to modify all
     4-bit condition fields, moving the value of the conditional
     register to a general-purpose register (mfcr) and comparing it
     with the expected one.

  o) Integer compare instructions

     This group will contain: cmp, cmpi, cmpl, cmpli.

     To verify these instructions the test will run them with
     different combinations of operands, read the condition register
     value and compare it with the expected one. More specifically,
     the test will contain a pre-built table containing the
     description of each test case: the instruction, the values of
     the operands, the condition field to save the result in and the
     expected result.

  o) Arithmetic instructions

     This group will contain: add, addc, adde, addme, addze, subf,
     subfc, subfe, subme, subze, mullw, mulhw, mulhwu, divw, divwu,
     extsb, extsh.

     The test will contain a pre-built table of instructions,
     operands, expected results and expected states of the condition
     register. For each table entry, the test will cyclically use
     different sets of operand registers and result registers. For
     example, for instructions that use 3 registers on the first
     iteration r0/r1 will be used as operands and r2 for result. On
     the second iteration, r1/r2 will be used as operands and r3 as
     for result and so on. This will enable to verify all
     general-purpose registers.

  o) Logic instructions

     This group will contain: and, andc, andi, andis, or, orc, ori,
     oris, xor, xori, xoris, nand, nor, neg, eqv, cntlzw.

     The test scheme will be identical to that from the previous
     point.

  o) Shift instructions

     This group will contain: slw, srw, sraw, srawi, rlwinm, rlwnm,
     rlwimi

     The test scheme will be identical to that from the previous
     point.

  o) Branch instructions

     This group will contain: b, bl, bc.

     The first 2 instructions (b, bl) will be verified by jumping to
     a fixed address and checking whether control was transfered to
     that very point. For the bl instruction the value of the link
     register will be checked as well (using mfspr). To verify the bc
     instruction various combinations of the BI/BO fields, the CTR
     and the condition register values will be checked. The list of
     such combinations will be pre-built and linked in U-Boot at
     build time.

  o) Load/store instructions

     This group will contain: lbz(x)(u), lhz(x)(u), lha(x)(u),
     lwz(x)(u), stb(x)(u), sth(x)(u), stw(x)(u).

     All operations will be performed on a 16-byte array. The array
     will be 4-byte aligned. The base register will point to offset
     8. The immediate offset (index register) will range in [-8 ...
     +7]. The test cases will be composed so that they will not cause
     alignment exceptions. The test will contain a pre-built table
     describing all test cases. For store instructions, the table
     entry will contain: the instruction opcode, the value of the
     index register and the value of the source register. After
     executing the instruction, the test will verify the contents of
     the array and the value of the base register (it must change for
     "store with update" instructions). For load instructions, the
     table entry will contain: the instruction opcode, the array
     contents, the value of the index register and the expected value
     of the destination register. After executing the instruction,
     the test will verify the value of the destination register and
     the value of the base register (it must change for "load with
     update" instructions).

  o) Load/store multiple/string instructions


The CPU test will run in RAM in order to allow run-time modification
of the code to reduce the memory footprint.

2.2.1.2 Special-Purpose Registers Tests

TBD.

2.2.1.3. Cache test

To verify the data cache operation the following test scenarios will
be used:

  1) Basic test #1

    - turn on the data cache
    - switch the data cache to write-back or write-through mode
    - invalidate the data cache
    - write the negative pattern to a cached area
    - read the area

    The negative pattern must be read at the last step

  2) Basic test #2

    - turn on the data cache
    - switch the data cache to write-back or write-through mode
    - invalidate the data cache
    - write the zero pattern to a cached area
    - turn off the data cache
    - write the negative pattern to the area
    - turn on the data cache
    - read the area

    The negative pattern must be read at the last step

  3) Write-through mode test

    - turn on the data cache
    - switch the data cache to write-through mode
    - invalidate the data cache
    - write the zero pattern to a cached area
    - flush the data cache
    - write the negative pattern to the area
    - turn off the data cache
    - read the area

    The negative pattern must be read at the last step

  4) Write-back mode test

    - turn on the data cache
    - switch the data cache to write-back mode
    - invalidate the data cache
    - write the negative pattern to a cached area
    - flush the data cache
    - write the zero pattern to the area
    - invalidate the data cache
    - read the area

    The negative pattern must be read at the last step

To verify the instruction cache operation the following test
scenarios will be used:

  1) Basic test #1

    - turn on the instruction cache
    - unlock the entire instruction cache
    - invalidate the instruction cache
    - lock a branch instruction in the instruction cache
    - replace the branch instruction with "nop"
    - jump to the branch instruction
    - check that the branch instruction was executed

  2) Basic test #2

    - turn on the instruction cache
    - unlock the entire instruction cache
    - invalidate the instruction cache
    - jump to a branch instruction
    - check that the branch instruction was executed
    - replace the branch instruction with "nop"
    - invalidate the instruction cache
    - jump to the branch instruction
    - check that the "nop" instruction was executed

The CPU test will run in RAM in order to allow run-time modification
of the code.

2.2.1.4. Memory test

The memory test will verify RAM using sequential writes and reads
to/from RAM. Specifically, there will be several test cases that will
use different patterns to verify RAM. Each test case will first fill
a region of RAM with one pattern and then read the region back and
compare its contents with the pattern. The following patterns will be
used:

 1) zero pattern (0x00000000)
 2) negative pattern (0xffffffff)
 3) checkerboard pattern (0x55555555, 0xaaaaaaaa)
 4) bit-flip pattern ((1 << (offset % 32)), ~(1 << (offset % 32)))
 5) address pattern (offset, ~offset)

Patterns #1, #2 will help to find unstable bits. Patterns #3, #4 will
be used to detect adherent bits, i.e. bits whose state may randomly
change if adjacent bits are modified. The last pattern will be used
to detect far-located errors, i.e. situations when writing to one
location modifies an area located far from it. Also, usage of the
last pattern will help to detect memory controller misconfigurations
when RAM represents a cyclically repeated portion of a smaller size.

Being run in normal mode, the test will verify only small 4Kb regions
of RAM around each 1Mb boundary. For example, for 64Mb RAM the
following areas will be verified: 0x00000000-0x00000800,
0x000ff800-0x00100800, 0x001ff800-0x00200800, ..., 0x03fff800-
0x04000000. If the test is run in power-fail mode, it will verify the
whole RAM.

The memory test will run in ROM before relocating U-Boot to RAM in
order to allow RAM modification without saving its contents.

2.2.2. Common tests

This section describes tests that are not based on any hardware
peculiarities and use common U-Boot interfaces only. These tests do
not need any modifications for porting them to another board/CPU.

2.2.2.1. I2C test

For verifying the I2C bus, a full I2C bus scanning will be performed
using the i2c_probe() routine. If any I2C device is found, the test
will be considered as passed, otherwise failed. This particular way
will be used because it provides the most common method of testing.
For example, using the internal loopback mode of the CPM I2C
controller for testing would not work on boards where the software
I2C driver (also known as bit-banged driver) is used.

2.2.2.2. Watchdog timer test

To test the watchdog timer the scheme mentioned above (refer to
section "Hazardous tests") will be used. Namely, this test will be
marked with the POST_REBOOT bit flag. On the first iteration, the
test routine will make a 10-second delay. If the system does not
reboot during this delay, the watchdog timer is not operational and
the test fails. If the system reboots, on the second iteration the
POST_REBOOT bit will be set in the flag argument to the test routine.
The test routine will check this bit and report a success if it is
set.

2.2.2.3. RTC test

The RTC test will use the rtc_get()/rtc_set() routines. The following
features will be verified:

  o) Time uniformity

     This will be verified by reading RTC in polling within a short
     period of time (5-10 seconds).

  o) Passing month boundaries

     This will be checked by setting RTC to a second before a month
     boundary and reading it after its passing the boundary. The test
     will be performed for both leap- and nonleap-years.

2.2.3. MPC8xx peripherals tests

This project will develop a set of tests verifying the peripheral
units of MPC8xx processors. Namely, the following controllers of the
MPC8xx communication processor module (CPM) will be tested:

  o) Serial Management Controllers (SMC)

  o) Serial Communication Controllers (SCC)

2.2.3.1. Ethernet tests (SCC)

The internal (local) loopback mode will be used to test SCC. To do
that the controllers will be configured accordingly and several
packets will be transmitted. These tests may be enhanced in future to
use external loopback for testing. That will need appropriate
reconfiguration of the physical interface chip.

The test routines for the SCC ethernet tests will be located in
cpu/mpc8xx/scc.c.

2.2.3.2. UART tests (SMC/SCC)

To perform these tests the internal (local) loopback mode will be
used. The SMC/SCC controllers will be configured to connect the
transmitter output to the receiver input. After that, several bytes
will be transmitted. These tests may be enhanced to make to perform
"external" loopback test using a loopback cable. In this case, the
test will be executed manually.

The test routine for the SMC/SCC UART tests will be located in
cpu/mpc8xx/serial.c.

2.2.3.3. USB test

TBD

2.2.3.4. SPI test

TBD

2.3. Design notes

Currently it is unknown how we will power off the board after running
all power-fail POST tests. This point needs further clarification.