FreeCalypso > hg > fc-magnetite
annotate doc/FCDEV3B-hardware-bug @ 560:d380b62e1019
tpudrv12.h: provision for future FCFAM triband-or-quadband support
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sat, 29 Dec 2018 04:06:37 +0000 (2018-12-29) |
parents | 15c61c8f3166 |
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1 Our current FCDEV3B boards exhibit a hardware bug: the reset input to the flash |
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2 chip is connected to Calypso's FDP output per both TI's Leonardo reference |
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3 schematics and Openmoko's working design, but this arrangement turns out to be |
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4 unsuitable for the high-capacity Spansion S71PL129NC0HFW4B flash+pSRAM chip we |
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5 are using, copied from Pirelli DP-L10. This hardware bug has manifested itself |
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6 in two different ways so far: |
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7 |
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8 * Out of the 20 boards we've built so far, on just one board there was an issue |
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9 where our standard Magnetite fw would have trouble booting from flash, but |
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10 RAM-loaded fw booted fine. Interrupting the boot process serially and having |
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11 the serially loaded code jump to the image in flash also worked fine. |
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12 Eventually it was found that the flash boot problem on that one board occurs |
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13 only when flash boot mode 1 is used, whereas flash boot mode 0 works fine. I |
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14 (Mychaela) suspect that the problem has something to do with the watchdog |
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15 reset that happens as part of flash boot mode 1, the FDP output behaviour |
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16 during that watchdog reset, and the flash chip's reaction to the latter. |
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17 |
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18 * On all of the boards there is a problem with sleep modes: when the firmware |
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19 is running from flash as opposed to RAM, certain sleep-wake sequences cause |
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20 an erratic self-reboot or a hang. Oscilloscope probing on a decased Pirelli |
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21 DP-L10 motherboard on which Calypso's FDP output is accessible seems to |
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22 confirm my (Mychaela's) suspicion that this FDP signal goes low during all |
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23 sleep modes, and the current working hypothesis is that our Spansion flash |
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24 chip gets unhappy with the reset timing it gets subjected to, and some flash |
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25 reads (instruction fetches) don't work after wakeup. So far the only workable |
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26 solution has been to disable all sleep modes in all FCDEV3B fw builds; |
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27 nothing else has been successful. However, re-enabling all of these sleep |
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28 modes with AT%SLEEP=4 works fine when the firmware image executes out of RAM |
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29 instead of flash, further supporting our current working hypothesis as to the |
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30 root cause. |
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31 |
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32 The fcdev3b-hacks directory contains two hacks that can be applied to FCDEV3B |
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33 firmware images (fwimage.bin builds) as xxd binary patches: |
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34 |
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35 * The first hack dating from 2017-05 patches the fw to use flash boot mode 0 |
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36 instead of TI's original flash boot mode 1, but after boot the FFFF:FB10 |
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37 register is set to put the flash and not the internal ROM at address 0, so |
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38 the interrupt and exception vectors go to the flash like in TI's original fw, |
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39 not through the internal ROM. This hack was put together for the purpose of |
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40 producing flashable fw images that boot without problems on that one board on |
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41 which flash boot mode 1 didn't work, and worked successfully for that purpose. |
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42 |
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43 * The second hack dating from 2018-03 patches the fw to not only use flash boot |
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44 mode 0, but also route the interrupt and exception vectors through Calypso's |
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45 internal ROM. I was hoping that this hack would make the sleep mode problem |
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46 go away by having the Calypso execute some cycles out of its internal ROM and |
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47 RAM before hitting the flash after wakeup, but nope, bringing up the SIM |
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48 interface with AT+CFUN=1 in the l1reconst config when running from flash with |
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49 small sleep enabled still triggers erratic misbehaviour even with this patch. |
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50 |
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51 The proper fix will require a new PCB spin to change the flash reset wiring: |
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52 instead of driving it with Calypso's FDP output, use the ON_nOFF master reset |
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53 signal from Iota's VRPC block, fed through a logic voltage level translating |
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54 buffer to change it from 1.5 V to 2.8 V logic. The flash chip we are using has |
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55 lower power consumption when it is NOT held in reset, hence unlike TI's intent |
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56 with FDP, we don't want our flash chip to go into reset during any sleep at all. |
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57 |
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58 The new PCB revision with this change is now in the process of being finalized, |
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59 and we will soon need the funding to produce the new boards. Anyone who is |
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60 interested in helping to make FCDEV3B V2 a reality should email Mychaela. |