Anastasia Klimchuk has submitted this change. ( https://review.coreboot.org/c/flashrom/+/83450?usp=email )
Change subject: doc: Add page with misc notes and advice ......................................................................
doc: Add page with misc notes and advice
This page is a combination of info from the following pages:
https://wiki.flashrom.org/Common_problems https://wiki.flashrom.org/Connections https://wiki.flashrom.org/FAQ https://wiki.flashrom.org/Random_notes https://wiki.flashrom.org/Live_CD
Change-Id: I538f31765576584760524cd8b06cbf5bce191bde Signed-off-by: Anastasia Klimchuk aklm@flashrom.org Reviewed-on: https://review.coreboot.org/c/flashrom/+/83450 Reviewed-by: Stefan Reinauer stefan.reinauer@coreboot.org Tested-by: build bot (Jenkins) no-reply@coreboot.org --- M doc/user_docs/index.rst A doc/user_docs/misc_notes.rst 2 files changed, 150 insertions(+), 0 deletions(-)
Approvals: build bot (Jenkins): Verified Stefan Reinauer: Looks good to me, approved
diff --git a/doc/user_docs/index.rst b/doc/user_docs/index.rst index b61567a..960659e 100644 --- a/doc/user_docs/index.rst +++ b/doc/user_docs/index.rst @@ -9,3 +9,4 @@ chromebooks management_engine misc_intel + misc_notes diff --git a/doc/user_docs/misc_notes.rst b/doc/user_docs/misc_notes.rst new file mode 100644 index 0000000..fcb1700 --- /dev/null +++ b/doc/user_docs/misc_notes.rst @@ -0,0 +1,149 @@ +===================== +Misc notes and advice +===================== + +This document contains miscellaneous and unstructured (and mostly, legacy) notes and advice about using flashrom. + +Command set tricks for parallel and LPC chips +============================================= + +This is only mentioned in very few datasheets, but it applies to some parallel (and some LPC) chips. + +Upper address bits of commands are ignored if they are not mentioned explicitly. If a datasheet specifies the following sequence:: + + chip_writeb(0xAA, bios + 0x555); + chip_writeb(0x55, bios + 0x2AA); + chip_writeb(0x90, bios + 0x555); + +then it is quite likely the following sequence will work as well:: + + chip_writeb(0xAA, bios + 0x5555); + chip_writeb(0x55, bios + 0x2AAA); + chip_writeb(0x90, bios + 0x5555); + +However, if the chip datasheet specifies addresses like ``0x5555``, you can't shorten them to ``0x555``. + +To summarize, replacing short addresses with long addresses usually works, but the other way round usually fails. + +flashrom doesn't work on my board, what can I do? +================================================= + +* First of all, check if your chipset, ROM chip, and mainboard are supported + (see :doc:`/supported_hw/index`). +* If your board has a jumper for BIOS flash protection (check the manual), disable it. +* Should your BIOS menu have a BIOS flash protection option, disable it. +* If you run flashrom on Linux and see messages about ``/dev/mem``, see next section. +* If you run flashrom on OpenBSD, you might need to obtain raw access permission by setting + ``securelevel = -1`` in ``/etc/rc.securelevel`` and rebooting, or rebooting into single user mode. + +What can I do about /dev/mem errors? +==================================== + +* If flashrom tells you ``/dev/mem mmap failed: Operation not permitted``: + + * Most common at the time of writing is a Linux kernel option, ``CONFIG_IO_STRICT_DEVMEM``, + that prevents even the root user from accessing hardware from user-space if the resource is unknown + to the kernel or a conflicting kernel driver reserved it. On Intel systems, this is most often ``lpc_ich``, + so ``modprobe -r lpc_ich`` can help. A more invasive solution is to try again after rebooting + with ``iomem=relaxed`` in the kernel command line. + + * Some systems with incorrect memory reservations (e.g. E820 map) may have the same problem + even with ``CONFIG_STRICT_DEVMEM``. In that case ``iomem=relaxed`` in the kernel command line may help too. + +* If it tells you ``/dev/mem mmap failed: Resource temporarily unavailable``: + + * This may be an issue with PAT (e.g. if the memory flashrom tries to map is already mapped + in an incompatible mode). Try again after rebooting with nopat in the kernel command line. + +* If you see this message ``Can't mmap memory using /dev/mem: Invalid argument``: + + * Your flashrom is very old, better update it. If the issue persists, try the kernel options mentioned above. + +* Generally, if your version of flashrom is very old, an update might help. + Flashrom has less strict requirements now and works on more systems without having to change the kernel. + +Connections +=========== + +Using In-System programming requires some means to connect the external programmer to the flash chip. + +Note that some external flashers (like the Openmoko debug board) lack a connector, +so they do requires some soldering to be used. Some other don't. For instance the buspirate has a pin connector on it. + +Programmer <-> Removable chip connection +---------------------------------------- + +A breadboard can be used to connect Dual in-line 8 pins chips to the programmer, as they they fit well into it. + +Programmer <-> Clip connection +------------------------------ + +If your programmer has a pin connector, and that you want to avoid soldering, you can use +**Short** `Jump Wires https://en.wikipedia.org/wiki/Jump_wire`_ to connect it to a clip. +They usually can be found on some electronic shops. + +Other issues +------------- + +* Wires length and connection quality: Long wires, and bad connection can create some issues, so avoid them. + + * The maximum wires length is very dependent on your setup, so try to have the shortest wires possible. + * If you can't avoid long wires and if you're flash chip is SPI, then lowering the SPI clock could make + it work in some cases. Many programmers do support such option (Called spispeed with most of them, or divisor with ft2232_spi). + +* When soldering wires, the wire tend to break near the soldering point. To avoid such issue, + you have to prevent the wires from bending near the soldering point. + To do that `Heat-shrink_tubing https://en.wikipedia.org/wiki/Heat-shrink_tubing`_ or similar methods can be used. + +Common problems +=============== + +The following describes problems commonly found when trying to access flash chips in systems +that are not designed properly for this job, e.g. ad-hoc setups to flash in-system +(TODO add a doc for in-system-specific problems). + +Symptoms indicating you may have at least one of these are for example inconsistent reads or probing results. +This happens basically because the analog electrical waveforms representing the digital information +get too distorted to by interpreted correctly all the time. Depending on the cause different steps can be tried. + +* Not all input pins are connected to the correct voltage level/output pin of the programmer. + Always connect all input pins of ICs! + +* The easiest thing to try is lowering the (SPI) clock frequency if your programmer supports it. + That way the waveforms have more time to settle before being sampled by the receiver which might be enough. + Depending on the design of the driver and receiver as well as the actual communication path + this might not change anything as well. + +* Wires are too long. Shortening them to a few cm (i.e. < 20, the lesser the better) might help. + +* The impedances of the wires/traces do not match the impedances of the input pins + (of either the circuit/chip on the mainboard or the external programmer). + Try using shorter wires, adding small (<100 Ohm) series resistors or parallel capacitors (<20pF) + as near as possible to the input pins (this includes also the MISO line which ends near the programmer)\ + and/or ask someone who has experience with high frequency electronics. + +* The supply voltage of the flash chip is not stable enough. Try adding a 0.1 µF - 1 µF (ceramic) capacitor + between the flash chip's VCC and GND pins as near as possible to the chip. + +Live CD +========= + +A Live CD containing flashrom provides a user with a stable work environment to read, write and verify a flash device on any supported hardware. + +It can help avoid Linux installation issues, which can be a hassle for some users. + +flashrom is already shipped in some of the Live CDs, see below. *Please note, some of these ship very old versions of flashrom*. + +* `SystemRescueCd http://www.sysresccd.org/`_ has been including flashrom since about version 2.5.1. + +* `grml http://grml.org/`_ + + * Note: You need the full grml ISO, "small" (and "medium") ISOs do not contain flashrom. + * Note: Some releases (e.g. 2011.12) did not contain flashrom. + +* `Parted Magic http://partedmagic.com/`_ + +* `Hiren's BootCD http://www.hirensbootcd.org/`_ + + * When you select "Linux based rescue environment (Parted Magic 6.7)" and then "Live with default settings", + you have access to a system which has flashrom.
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Anastasia Klimchuk (Code Review)