Thursday, 30 April 2015

Linksys NSLU2 JTAG help requested

Some time ago I have embarked on a jurney to install NetBSD on one of my two NSLU2-s. I have ran into all sorts of hurdles and problems which I finally managed to overcome, except one:

The NSLU I am using has a standard 20 pin ARM JTAG connector attached to it (as per this page, only TDI, TDO, TMS, TCK, Vref and GND signals), but, although the chip is identified, I am unable to halt the CPU:
    $ openocd -f interface/ftdi/olimex-arm-usb-ocd.cfg -f board/linksys_nslu2.cfg
    Open On-Chip Debugger 0.8.0 (2015-04-14-09:12)
    Licensed under GNU GPL v2
    For bug reports, read
    Info : only one transport option; autoselect 'jtag'
    adapter speed: 300 kHz
    Info : ixp42x.cpu: hardware has 2 breakpoints and 2 watchpoints
    Info : clock speed 300 kHz
    Info : JTAG tap: ixp42x.cpu tap/device found: 0x29277013 (mfg: 0x009,
    part: 0x9277, ver: 0x2)
    $ telnet localhost 4444
    Trying ::1...
    Connected to localhost.
    Escape character is '^]'.
    Open On-Chip Debugger
    > halt
    target was in unknown state when halt was requested
    in procedure 'halt'
    > poll
    background polling: on
    TAP: ixp42x.cpu (enabled)
    target state: unknown
My main goal is to make sure I can  flash the device via JTAG, in case I break it, but it would be ideal if I could use the JTAG to single step through the code.

I have found that other people have managed to flash the device via JTAG without the other signals, and some have even changed the bootloader (and had JTAG confirmed as backup solution), so I am stuck.

So if anyone can give some insights into ixp42x / Xscale / NSLU2 specific JTAG issues or hints regarding this issue on OpenOCD or other such tool, I would be really grateful.

Note: I have made a hacked second stage Apex bootloader to laod the NetBSD image via TFTP, but the default RedBoot sequence 'boot; exec 0x01d00000' should be 'boot; go 0x01d00000' for NetBSD to work, so I am considering changing the RedBoot partition to alter that command. The gory details can be summed as my Apex is calling RedBoot functions to be network enabled (because Intel's NPE current code is not working on Apex) and I have tested this to work with go, but not with exec.

Monday, 6 April 2015

HOWTO: Dnsmasq server for network booting using TFTP and DHCP

Dnsmasq is a very lightweight server that besides the expected DNS caching functionality, it also offers DHCP and TFTP functionality in a single binary.

This makes it very useful if one needs to network boot a system since you can have the TFTP and DHCP part of the setup done easily, and only add NFS for a complete network boot.

Add to that that

One extra nice thing dnsmasq has is that it can mark specific hosts, addresses or ranges with some internal markers, then use those markers as symbolic names to apply settings based for classes of devices.

In the configuration snippet below, there is a rule I set up to make sure I would apply the 'netbsd' label to any system connecting through specific ethernet interfaces (one is the interface of the system, the other is a USB NIC I use from time to time):
#You will need a range for static IPs in the main file

# give the name 'kinder' to any machine connecting through the given ethernet nics and apply 'netbsd' label
dhcp-host=00:1a:70:99:60:BB,00:06:4F:0D:B1:95, kinder,, set:netbsd

# Machines tagged 'netbsd' shall use the given NFS root path
dhcp-option=tag:netbsd, option:root-path,/export/netbsd-nslu2/root
# Enable dnsmasq's built-in TFTP server

# Set the root directory for files available via FTP.
Saving this configuration file in /etc/dnsmasq.d/kinder-netboot will enable this to be used by dnsmasq if this line is present in /etc/dnsmasq.conf
Commenting it will disable the netbsd part easily.