SRM console is used by Alpha systems as Unix-style boot firmware. Tru64 Unix and OpenVMS depend on it and Linux can boot from it. You can recognize SRM console as a blue screen with a prompt that is presented to you on power-up.
Most Alpha systems have both the SRM and ARC/AlphaBIOS console in
their firmware. On one of these machines, if your machine starts up
with ARC/AlphaBIOS by default, you can switch to SRM through the
"Console Selection" option in the Advanced CMOS Setup menu. To make
the change permanent, you should set the os_type environment
variable in SRM to "OpenVMS" or "Unix", like this:
>>> set os_type Unix
Either one will work to boot Linux. However, if you intend to
dual-boot OpenVMS on this machine, you must set os_type to
"OpenVMS". Conversely, to return to ARC/AlphaBIOS, you can set
os_type to "NT".
Some older systems may not have both SRM and ARC in firmware as shipped. On these systems, you will have to upgrade your firmware. See http://ftp.digital.com/pub/DEC/Alpha/firmware/ for the latest firmware updates and instructions.
A few older systems (primarily evaluation boards such as the 164SX
and 164LX) are "half-flash" systems, whose firmware can hold SRM or
AlphaBIOS, but not both. If you have one of these machines, you will
have to reflash your firmware with the SRM console using the AlphaBIOS
firmware update utility. Again, see
http://ftp.digital.com/pub/DEC/Alpha/firmware/ for firmware
images and instructions. If you wish to return to AlphaBIOS on these
machines, you may rerun the firmware update utility from a floppy in
SRM using the fwupdate command. You can also start AlphaBIOS
from a floppy using the arc command.
The SRM console works very much like a Unix or OpenVMS shell. It
views your NVRAM and devices as a pseudo-filesystem. You can see this
if you use the ls command. Also, it contains a fairly large set
of diagnostic, setup, and debugging utilities, the details of which
are beyond the scope of this document. As in the Unix shell, you can
pipe the output of one command to the input of another, and there is a
more command that works not unlike the Unix one. To get a full
listing of available commands, run:
>>> help | more
As well, SRM has environment variables, a number of which are
pre-defined and correspond to locations in NVRAM. You can view the
entire list of environment variables and their values with the
show command (there are quite a few of them, so you will probably
want to pipe its output to more). You can also show variables
matching a "glob" pattern - for example, show boot* will show all
the variables starting in "boot".
Environment variables are categorized as either read-only,
warm non-volatile, or cold non-volatile. The full listing
of pre-defined variables is detailed in the Alpha Architecture
Reference Manual. The most useful pre-defined environment variables
for the purposes of booting Linux are bootdef_dev,
boot_file, boot_flags, and
auto_action, all of which are cold non-volatile.
To set environment variables, use the set command, like this:
>>> set bootdef_def dka0
If you set an undefined variable, it will be created for you, however it will not persist across reboots.
The bootdef_dev variable specifies the device (using
VMS naming conventions - see
device naming
for an
explanation of these) which will be booted from if no device is
specified on the boot command line, or in an automatic boot.
The boot_file variable contains the filename to be
loaded by the secondary bootloader, while boot_flags
contains any extra flags. auto_action specifies the
action which the console should take on power-up. By default, it is
set to HALT, meaning that the machine will start up in the
SRM console. Once you have configured your bootloader and the
boot-related variables, you can set it to BOOT in order to
boot automatically on power-up.
Finally, two helpful console keystrokes you should know are Control-C, which, as in the shell, halts a command in progress (such as an automatic boot), and Control-P, which if issued from the aboot prompt (or other secondary bootloader) will halt the bootloader and return you to the SRM console.
All versions of SRM can boot from SCSI disks and the versions for
recent platforms, such as the Noname or AlphaStations can boot from
floppy disks as well. Network booting via bootp is supported.
Note that older SRM versions (notably the one for the Jensen)
cannot boot from floppy disks. Booting from IDE devices
is supported on newer platforms (DS20, DS10, DP264, UP2000 etc..).
Booting Linux with SRM is a two step process: first, SRM loads and transfers control to the secondary bootstrap loader. Then the secondary bootstrap loader sets up the environment for Linux, reads the kernel image from a disk filesystem and finally transfers control to Linux.
Currently, there are two secondary bootstrap loaders for Linux:
the raw loader that comes with the Linux kernel and aboot
which is distributed separately. These two loaders are described in
more detail below.
SRM knows nothing about filesystems or disk-partitions. It simply expects that the secondary bootstrap loader occupies a consecutive range of physical disk sector, starting from a given offset. The information on the size of the secondary bootstrap loader and the offset of its first disk sector is stored in the first 512 byte sector. Specifically, the long integer at offset 480 stores the size of the secondary bootstrap loader (in 512-byte blocks) and the long at offset 488 gives the sector number at which the secondary bootstrap loader starts. The first sector also stores a flag-word at offset 496 which is always 0 and a checksum at offset 504. The checksum is simply the sum of the first 63 long integers in the first sector.
If the checksum in the first sector is correct, SRM goes ahead and
reads the size sectors starting from the sector given in the
sector number field and places them in virtual memory at
address 0x20000000. If the reading completes successfully,
SRM performs a jump to address 0x20000000.