2017-07-25 13:15:59 +02:00
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# Support code to run on EV3 brick
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## Kernel module
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Kernel module is based on LEGO's `d_usbdev` module, with the addition of slightly modified `g_mass_storage`
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module from the Linux kernel. The module and supporting sources are licensed under GPLv2 (since
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they are derived from GPLv2 code).
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### Modifications
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* the `d_usbdev` uses the composite framework to register an additional mass storage function in addtion
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to the pre-existing custom USB HID function
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* the `g_mass_storage` module has the following changes:
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* additional `/sys/.../lun0/active` entry is added, which allows for signaling drive eject to the host
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2017-07-27 15:36:01 +02:00
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* `d_usbdev` has an additional `ioctl()` to pretend data came from the USB host - this can be used to direct
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the VM to do stuff
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2017-07-25 13:15:59 +02:00
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### Kernel modifications
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The kernel itself has modified FIFO queue sizes. The LEGO kernel uses `1024` for `ep1in` and `ep1out`,
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and then `64` for `ep2` and `ep3`. Note that this is non-standard modification done with a kernel patch,
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that I didn't manage to find. The MSD requires `512` for `ep2` and `ep3`. I have binary edited the kernel
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to do so.
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Note that there's 4k of FIFO memory in the hardware. If you set the queue sizes with a sum of more than
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4k, the kernel will hang, and you will not know why.
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## UF2 Daemon
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The [UF2](https://github.com/Microsoft/uf2) daemon is based on
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[UF2 ATSAMD21](https://github.com/Microsoft/uf2-samd21) bootloader code. It exposes a virtual
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FAT16 file system over Linux Network Block Device interface (`/dev/nbd0` to be precise).
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This device is then exposed via the `g_mass_storage` module to the host computer.
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The Daemon is licensed under MIT.
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