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+++ b/doc/Flash-boot-defect	Tue May 02 03:24:30 2017 +0000
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+As of this writing (2017-05-01), there is an unexplained hardware problem on
+some of our FCDEV3B boards in that flashed firmware images which use flash boot
+mode 1 (see the Flash-boot-modes article) fail to boot.  It is not currently
+known how many boards are affected by this problem; it is possible that the
+Mother's S/N 001 board is the only one that exhibits this oddity.
+
+This problem particularly affects our FC Magnetite firmware, as the latter uses
+flash boot mode 1 just like TI's TCS211 fw from which it originates.  OTOH, our
+FC Citrine firmware, which uses flash boot mode 0, boots just fine.  A minimal
+test case has been created under target-utils/flash-boot-test in this
+repository: it is a simple loadagent-like standalone application that is built
+to be booted from flash instead of expecting to be loaded serially, and it is
+built in two versions, one for mode 0 and another for mode 1.  Both versions
+work on an Openmoko-made GTA02 (the mode 1 version continuously reboots every
+few seconds because it doesn't disable the watchdog timer, but it is still very
+clearly alive) as well as on those FCDEV3B boards which aren't affected, but on
+FCDEV3B S/N 001 the mode 1 version fails to boot just like the full Magnetite
+firmware.
+
+The Mother of FreeCalypso does not currently have any prognosis as to when or
+even if the mysterious hardware problem that causes flash boot mode 1 to fail
+can be fixed.  Logical reasoning tells us that it must be a hardware problem,
+as the flash boot mode in question works without a hitch on every pre-existing
+Calypso device known to us, and similar logical reasoning tells us that the
+watchdog timer probably has to be involved in some way, as it is the mechanism
+underlying flash boot mode 1 (again, see the Flash-boot-modes article), but I
+am at a total loss when it comes to what kind of board-level problem could
+possibly produce such behaviour.  But then if only the S/N 001 board is affected
+and no others, it could just be a defective chip.  More data points need to be
+gathered before we shall know whether or not we have a real problem.
+
+For those who do have a flash-boot-challenged FCDEV3B board, two workarounds
+have been developed, in this chronological order:
+
+1. One can boot the board in the serial download mode, and download a
+   teensy-tiny piece of code that disables the boot ROM and jumps to address 0.
+   If the flash contains a firmware image meant to be booted in mode 1, this
+   image will get indirectly booted in this manner.  Run a command like this:
+
+fc-iram -h fcfam /dev/ttyXXX /opt/freecalypso/target-bin/flash-boot-wa.srec rvinterf
+
+(fc-iram has been extended to support second program invokation just like
+ fc-xram, just for this peculiar use case.  The flash-boot-wa.srec helper can
+ also be booted via fc-xram.)
+
+2. After doing the above, I found a way to patch the Magnetite firmware image
+   to boot in mode 0 - see the Flash-boot-mode-hack write-up in the Magnetite
+   source tree.  With this patch applied, FC Magnetite happily boots directly
+   from flash on my board without needing fc-iram or fc-xram assistance.