FreeCalypso > hg > freecalypso-tools
comparison doc/Flash-boot-defect @ 205:de8f75783b3b
Flash-boot-defect and Flash-boot-modes documentation
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Tue, 02 May 2017 03:24:30 +0000 |
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| 204:064d4eedb3a6 | 205:de8f75783b3b |
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| 1 As of this writing (2017-05-01), there is an unexplained hardware problem on | |
| 2 some of our FCDEV3B boards in that flashed firmware images which use flash boot | |
| 3 mode 1 (see the Flash-boot-modes article) fail to boot. It is not currently | |
| 4 known how many boards are affected by this problem; it is possible that the | |
| 5 Mother's S/N 001 board is the only one that exhibits this oddity. | |
| 6 | |
| 7 This problem particularly affects our FC Magnetite firmware, as the latter uses | |
| 8 flash boot mode 1 just like TI's TCS211 fw from which it originates. OTOH, our | |
| 9 FC Citrine firmware, which uses flash boot mode 0, boots just fine. A minimal | |
| 10 test case has been created under target-utils/flash-boot-test in this | |
| 11 repository: it is a simple loadagent-like standalone application that is built | |
| 12 to be booted from flash instead of expecting to be loaded serially, and it is | |
| 13 built in two versions, one for mode 0 and another for mode 1. Both versions | |
| 14 work on an Openmoko-made GTA02 (the mode 1 version continuously reboots every | |
| 15 few seconds because it doesn't disable the watchdog timer, but it is still very | |
| 16 clearly alive) as well as on those FCDEV3B boards which aren't affected, but on | |
| 17 FCDEV3B S/N 001 the mode 1 version fails to boot just like the full Magnetite | |
| 18 firmware. | |
| 19 | |
| 20 The Mother of FreeCalypso does not currently have any prognosis as to when or | |
| 21 even if the mysterious hardware problem that causes flash boot mode 1 to fail | |
| 22 can be fixed. Logical reasoning tells us that it must be a hardware problem, | |
| 23 as the flash boot mode in question works without a hitch on every pre-existing | |
| 24 Calypso device known to us, and similar logical reasoning tells us that the | |
| 25 watchdog timer probably has to be involved in some way, as it is the mechanism | |
| 26 underlying flash boot mode 1 (again, see the Flash-boot-modes article), but I | |
| 27 am at a total loss when it comes to what kind of board-level problem could | |
| 28 possibly produce such behaviour. But then if only the S/N 001 board is affected | |
| 29 and no others, it could just be a defective chip. More data points need to be | |
| 30 gathered before we shall know whether or not we have a real problem. | |
| 31 | |
| 32 For those who do have a flash-boot-challenged FCDEV3B board, two workarounds | |
| 33 have been developed, in this chronological order: | |
| 34 | |
| 35 1. One can boot the board in the serial download mode, and download a | |
| 36 teensy-tiny piece of code that disables the boot ROM and jumps to address 0. | |
| 37 If the flash contains a firmware image meant to be booted in mode 1, this | |
| 38 image will get indirectly booted in this manner. Run a command like this: | |
| 39 | |
| 40 fc-iram -h fcfam /dev/ttyXXX /opt/freecalypso/target-bin/flash-boot-wa.srec rvinterf | |
| 41 | |
| 42 (fc-iram has been extended to support second program invokation just like | |
| 43 fc-xram, just for this peculiar use case. The flash-boot-wa.srec helper can | |
| 44 also be booted via fc-xram.) | |
| 45 | |
| 46 2. After doing the above, I found a way to patch the Magnetite firmware image | |
| 47 to boot in mode 0 - see the Flash-boot-mode-hack write-up in the Magnetite | |
| 48 source tree. With this patch applied, FC Magnetite happily boots directly | |
| 49 from flash on my board without needing fc-iram or fc-xram assistance. |