144 lines
5.8 KiB
Plaintext
144 lines
5.8 KiB
Plaintext
$NetBSD: README,v 1.5 2006/05/18 20:13:14 imp Exp $
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NetBSD for the Linksys NSLU2 (a.k.a. "Slug")
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The NSLU2 (Network Storage Link for USB 2.0 Disk Drives) is a small, cheap
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NAS device consisting of an Intel IXP420 (Xscale) CPU, a 10/100mbit Ethernet
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port, and two USB 2.0 ports. It has 32MB of SDRAM and 8MB of Flash memory,
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and runs RedBoot/Linux out of the box.
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It is eminently hackable.
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The guys over at http://www.nslu2-linux.org/ have done a good job of
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documenting just about every aspect of the hardware and original firmware.
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They also provide a custom "Unslung" Linux distribution to replace the
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original hobbled kernel/userland.
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Because of the amount of documentation available, and the fact that Slugs
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are available so cheaply (I paid just over UKP 50 for mine, brand new) I
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decided to buy one and port NetBSD to it.
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This is the result of that effort.
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Note: The Slug's IXP420 CPU runs in big-endian mode, so when building a
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cross toolchain you must pass "-m evbarm -a armeb" to build.sh.
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Current status
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==============
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The following bits of Slug hardware are not (yet?) supported:
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- NPE Ethernet
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Someone will have to port Intel's IXP425 access library before this can
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be made to work. If that someone is you, the source code is available
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online here:
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http://www.intel.com/design/network/products/npfamily/ixp425.htm
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Look under "Tools & Software", then select "Intel(R) IPXX400 Software"
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to downlod the documentation. If you aren't registered, select
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"Register/Login" first. Documentation is available in the
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"Technical Documents" section.
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The easiest option will be to download the non-crypto version of the
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Access Library. The crypto-enabled version requires a lot more form
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filling. The Slug's IXP420 has no crypto capabilities anyway.
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- Flash ROM
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You can write gzboot kernels (when support is added) to Flash using
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RedBoot, so all is not lost.
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- Buzzer
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In the absence of a decent API to expose the onboard buzzer to userland,
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this is not yet supported. I envisage using timer1 to generate an
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interrupt at the required rate (1-2 kHz). The handler will toggle the
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buzzer GPIO pin. Obviously timer1 will be configured only when necessary
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as a 1-2 kHz interrupt rate will sap a fair bit of CPU horsepower.
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Everything else is fully supported, including the power/reset buttons and
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disk activity/status LEDs.
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Non-hardware items on the TODO list include:
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- gzboot support.
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The Slug's 8MB of Flash is split into 5 segments:
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1 0x50000000-0x5003ffff: RedBoot (with some additional bits at the end).
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2 0x50040000-0x5005ffff: Sysconf (used by the Linksys firmware).
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3 0x50060000-0x5015ffff: Self-extracting compressed kernel image.
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4 0x50160000-0x507dffff: Compressed ramdisk image.
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5 0x507e0000-0x507fffff: SerComm Flash trailer.
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Segments 1, 2, and 5 should be considered immutable. Segments 3 and 4
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have a 16-byte header, the first 4 bytes of which describe the length
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of the image contained in that segment (not including the header).
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On power-up, RedBoot copies the image in segment 3 into SDRAM at 0x01d00000,
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and the image in segment 4 into SDRAM at 0x01000000. RedBoot then jumps to
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0x01d00000. This is just a regular ARM Linux compressed kernel bootloader.
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So, we need to create a version of gzboot linked not at Flash address
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0x50060000, but at 0x01d00000 instead. The only downside is that it looks
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like the combined size of gzboot plus compressed kernel cannot exceed 1MB.
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To support an md(4) root filesystem, we will need to modify gzboot to
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decompress the ramdisk image from segment 4 and copy it to the correct
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place in the decompressed kernel image.
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- Move the kernel link address closer to the start of SDRAM. We waste a
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little under 2MB with the current setup.
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Getting NetBSD onto the NSLU2
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=============================
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Thanks to the efforts of the guys over at www.nslu2-linux.org, hacking the
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Slug is a pretty easy proposition, but some soldering skills are essential.
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For a first-time install of NetBSD (at least until someone comes up with a
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nice easy binary install image) you will almost certainly require access to
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the serial console. This means firing up your trusty soldering iron and
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hooking up a MAX3232 chip to your Slug. While your soldering iron is hot,
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you should seriously consider de-restricting your Slug's CPU core clock
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speed (133MHz stock, 266MHz de-restricted) by removing a single surface-
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mount resistor. Full instructions for both the these mods are on the above
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website.
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Once you have console access you can interrupt RedBoot's auto-boot process
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using CTRL-C. You are now in a position to download a NetBSD kernel into
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SDRAM.
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You will have to configure a TFTP server on a machine hooked up to the same
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Ethernet segment as the Slug. This machine's Ethernet interface must also
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be configured to have an address in the 192.168.0.0/24 subnet since the
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Slug's Ethernet *always* defaults to 192.168.0.1 when running RedBoot.
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There seems to be no way to alter this, so the best course of action will
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probably be to set up an alias on the server's interface. 192.168.0.2 is
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a good choice.
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Assuming you've done all that and have dropped a suitable kernel image
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into the TFTP directory, the following commands will load and run the
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kernel.
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redboot> ip_address -h 192.168.0.2
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redboot> load -r -b 0x200000 netbsd.bin
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redboot> go
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At this point your only real option is to mount the root filesystem from
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a USB disk device as the onboard Ethernet is not (yet?) supported. However,
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there's nothing to stop you using a USB-Ethernet interface...
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Note that the kernel will always report the CPU core clock speed as 266MHz
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even if your Slug's CPU clock is running at a stock 133MHz.
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Burning a NetBSD kernel into Flash
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==================================
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TBD (waiting for gzboot support).
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