mirror of
https://github.com/MiSTer-devel/CDi_MiSTer.git
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74bff4c5ce
Added ioctl_download for slave rom boot0.rom is expected to be the main cpu rom boot1.rom is expected to be the slave rom
70 lines
3.0 KiB
Markdown
70 lines
3.0 KiB
Markdown
# Bootup
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We need to get the ROM into the SDRAM
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## How does PSX and the Mega CD do it?
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Inside psx.cpp there is `load_bios()`. It is called by `psx_mount_cd()`.
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But who calls it? From menu.cpp? But why is it called?
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Inside megacd.cpp there is `mcd_set_image()`. Inside `MegaCD.sv` there is
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```verilog
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wire rom_download = ioctl_download & (ioctl_index[5:0] <= 6'h01);
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```
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But where does this come from?
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Ok, everything revolves around `user_io_file_tx()`
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It even says something like this
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```c
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// set index byte (0=bios rom, 1-n=OSD entry index)
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```
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## How does the CD-i do it?
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Experiment:
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/media/fat/games/CD-i# hexdump -C boot0.rom | head
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00000000 6a 85 25 11 57 cc fd 49 4a d1 56 82 01 29 fb 21 |j.%.W..IJ.V..).!|
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00000010 91 02 3b 71 36 b1 71 d0 e7 17 52 db 19 fa e2 70 |..;q6.q...R....p|
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00000020 97 29 33 00 9e 88 f6 86 3a b8 a5 6f 70 c0 17 09 |.)3.....:..op...|
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00000030 02 68 9b 06 78 68 53 3d 55 37 24 b3 3b 33 f8 cc |.h..xhS=U7$.;3..|
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00000040 3d fa 13 98 76 72 54 5b e3 8c a0 46 91 9f f8 4f |=...vrT[...F...O|
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00000050 71 39 9e e6 4b 57 47 8c 54 2c 6d 05 7a fe 4f 77 |q9..KWG.T,m.z.Ow|
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00000060 b8 b7 96 0b 5f 6e fc 55 d1 01 7f cb e6 64 4a 81 |...._n.U.....dJ.|
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00000070 57 da 80 0b 24 e5 66 8b 7d 5c 21 8a 9f d5 af b2 |W...$.f.}\!.....|
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00000080 0c f0 9e 83 9b 71 51 bb ea 14 da 1a 1c b8 f3 14 |.....qQ.........|
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00000090 8a 99 58 aa bf e5 b1 c7 85 5a 98 98 ad 74 a6 e9 |..X......Z...t..|
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/media/fat/games/CD-i# hexdump -C boot1.rom | head
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00000000 00 00 15 00 00 40 04 b8 00 00 05 00 00 00 05 0a |.....@..........|
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00000010 00 00 05 14 00 00 05 1e 00 00 05 28 00 00 05 32 |...........(...2|
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00000020 00 00 05 3c 00 00 05 46 00 00 05 50 00 00 05 5a |...<...F...P...Z|
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00000030 00 00 05 64 00 00 05 6e 00 00 05 78 00 00 05 82 |...d...n...x....|
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00000040 00 00 05 8c 00 00 05 96 00 00 05 a0 00 00 05 aa |................|
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00000050 00 00 05 b4 00 00 05 be 00 00 05 c8 00 00 05 d2 |................|
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00000060 00 00 05 dc 00 00 05 e6 00 00 05 f0 00 00 05 fa |................|
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00000070 00 00 06 04 00 00 06 0e 00 00 06 18 00 00 06 22 |..............."|
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00000080 00 00 06 2c 00 00 06 36 00 00 06 40 00 00 06 4a |...,...6...@...J|
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00000090 00 00 06 54 00 00 06 5e 00 00 06 68 00 00 06 72 |...T...^...h...r|
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Let's see!
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ioctl_index[15:0] starts with 0000h.
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First data in word mode is 0x856a. Afterwards it is 0x1125. This means we have a little endian word here.
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Boot0.rom is transmitted.
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Afterwards...
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ioctl_index[15:0] is set to 0040h.
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First data in word mode is 0. Afterwards it is 0x0015. This means we have a little endian word here.
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Boot1.rom is transmitted.
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Can is use ioctl_index[6] to mark the slave worm data?
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## References
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https://github.com/alanswx/Tutorials_MiSTer/tree/master/basic/lesson2/rtl
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https://github.com/alanswx/Tutorials_MiSTer/tree/master/basic/lesson2
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https://mister-devel.github.io/MkDocs_MiSTer/developer/hps_io/#rom-and-file-loading-nvram-saving
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