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annotate compal/c139-boot.notes @ 379:a760a5eeed65

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compal/audio/omr-guide: another avenue of investigation
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 10 Oct 2021 19:53:35 +0000
parents 49c7cda96f04
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
105
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
1 Download protocol, attempted first at 406250 baud, then 115200, only on the
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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2 MODEM UART:
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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3
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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4 The boot code begins by transmitting 1B F6 02 00 41 01 40, then calls the
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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5 Rx-with-timeout function 7 times, expecting this seq: 1B F6 02 00 52 01 53.
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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6 Getting anything else or timeout causes the 0xbac function to return,
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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7 ending that download attempt. If this seq was received, the boot code then
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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8 sends 1B F6 02 00 41 02 43 and expects to receive 3 bytes as follows:
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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9
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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10 * one dummy byte (stored into an automatic var, but then not used)
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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11 * payload length MSB
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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12 * payload length LSB
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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13
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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14 The boot code then expects to receive the specified # of bytes [0,65535]
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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15 and stores them beginning at 0x800100. Then the Rx-with-timeout function
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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16 is called again to receive the XOR checksum byte, not counted in the length.
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
17 If the checksum fails to match, 0xbac function sends 1B F6 02 00 45 53 16
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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18 and returns. If this check passes, the "1003" check is performed next:
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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19 the 4 bytes starting at 0x803ce0 must match. If the downloaded image was
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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20 shorter, the comparison will be made against pre-powerup IRAM content,
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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21 i.e., law of chance. Furthermore, the comparison is actually an inequality:
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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22 each "signature" byte in the downloaded image needs to be >= (in the signed
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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23 sense) than the "1003" reference. (0x7F7F7F7F thus ought to be a passing
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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24 value.)
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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25
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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26 If this last check passes, the 0xbac function jumps to the downloaded image
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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27 instead of returning. Control is transferred to 0x800100 in the ARM state.
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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28 If the "1003" check fails, 0xbac function sends 1B F6 02 00 41 03 57
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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29 and returns.
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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30
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
31 If the boot process is not diverted to a successful serial download as above,
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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32 the boot code does one strange thing before it jumps to 0x20f8 (main app entry
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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33 point). The boot code unconditionally transmits "ftmtool" on the MODEM UART
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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34 and waits a certain time for a "yes" response. If it receives that "yes",
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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35 it responds with "modemerror", otherwise just "error". Either way, it then
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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36 proceed to jump to the main app entry point at 0x20f8! There is also a bunch
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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37 of "dead" code in the 8 KiB "boot block", code which does not seem to be
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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38 reachable from any path. There is no check for whether or not the "main app"
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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39 is present; if the flash contains the 8 KiB "boot block" followed by blank
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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40 space, the boot code will happily jumps to those FFs - but it will still
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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41 provide an opportunity for serial download as usual, so no real problem.
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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42
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
43 IRAM variables used by the boot code:
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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44
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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45 83FF00 holds UART base addr, set to FFFF5800 (MODEM)
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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46 83FF08 32-bit var init to 0
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
47 83FF10 32-bit var init to 0
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
48 83FF80 byte var init to 0 at the beginning of ftmtool function (0xdbe),
49c7cda96f04 C139 boot ROM fully cracked
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
49 set to 1 if "yes" received in response to "ftmtool"