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annotate bootrom.notes @ 7:a445735685ba

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boot ROM re: flash application image interface documented
author Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
date Tue, 16 Apr 2013 20:56:31 +0000
parents e3f8fe6a848e
children a06573cacb6e
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7
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
1 Application images in flash:
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
2
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
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3 In order for the nCS0 flash content to be considered a valid bootable image
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
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4 (i.e., for the boot ROM to transfer control to it, rather than wait forever
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
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5 for a UART download), the 32-bit word at address 0x2000 (the first word
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
6 after the ROM-overlaid portion) must contain either 0 or 1, corresponding
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
7 to two supported environment options:
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
8
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
9 * If the word at 0x2000 equals 0, it signifies an application image that is
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
10 designed to run with the boot ROM still mapped at 0, with ARM exceptions
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
11 vectoring through the 7 magic RAM locations at 0x80001C, and possibly
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
12 through the 2nd level ("user-friendly") vector table at 0x800000 as well.
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
13
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
14 If the word at 0x2000 equals 0, the following word at 0x2004 must contain
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
15 the absolute address of the boot entry point; the boot ROM will transfer
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
16 control to that address with the FFFF:FB10 register set to explicitly map
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
17 the internal boot ROM at 0. It is a BX-style address: setting the least
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
18 significant bit will result in control being transferred in the Thumb state.
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
19
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
20 * If the word at 0x2000 equals 1, it signifies an application image that is
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
21 at least conceptually independent of the Calypso boot ROM - one that would,
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
22 at least in theory, function correctly with nIBOOT tied/pulled/driven HIGH,
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
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23 or even on an older DBB chip with no internal boot ROM.
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
24
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
25 When the boot ROM code sees a 1 in the 0x2000 word, it copies a little piece
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
26 of code into the internal ROM and runs it there; this code sets the FFFF:FB10
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
27 register to disable the internal boot ROM (map the external nCS0 memory at 0,
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
28 as if nIBOOT were high) and causes the watchdog timer to go off, resetting
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
29 the ARM core and causing it to execute the external nCS0 reset vector.
a445735685ba boot ROM re: flash application image interface documented
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents: 3
diff changeset
30
3
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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31 RAM layout:
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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32
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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33 800000 7 words:
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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34 soft-vector pointers: by default the following 7 words at
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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35 80001C are filled with ldr-jump instructions, which read
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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36 from these 7 words and load them into PC
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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37 80001C 7 words:
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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38 hard vectors: the physical vector locations in the ROM
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
39 contain branch instructions to these 7 RAM addresses
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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40
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
41 800104: word initialized to 0x0001D4C0
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
42 800108: byte initialized to 0x01
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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43
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
44 800534: byte initialized to 0x00
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
45
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
46 8005C0: appears to be the intended low address (bottom) of the stack
e3f8fe6a848e boot ROM re: started on main() and the 0xe2c routine
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
47 80074C: top of the stack (initial value loaded into SP)