441 lines
9.5 KiB
HTML
441 lines
9.5 KiB
HTML
<HTML
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>What is SRM?</TITLE
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>SRM Firmware Howto</TH
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="AEN31"
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>2. What is SRM?</A
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></H1
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><P
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>SRM console is used by Alpha systems as
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Unix-style boot firmware. Tru64 Unix and OpenVMS depend on it and
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Linux can boot from it. You can recognize SRM console as a blue screen
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with a prompt that is presented to you on power-up.</P
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="AEN34"
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>2.1. Getting to SRM</A
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></H2
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><P
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>Most Alpha systems have both the SRM and ARC/AlphaBIOS console in
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their firmware. On one of these machines, if your machine starts up
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with ARC/AlphaBIOS by default, you can switch to SRM through the
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"Console Selection" option in the Advanced CMOS Setup menu. To make
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the change permanent, you should set the <TT
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CLASS="LITERAL"
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>os_type</TT
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> environment
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variable in SRM to "OpenVMS" or "Unix", like this:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>>>> set os_type Unix</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>Either one will work to boot Linux. However, if you intend to
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dual-boot OpenVMS on this machine, you must set <TT
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CLASS="LITERAL"
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>os_type</TT
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> to
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"OpenVMS". Conversely, to return to ARC/AlphaBIOS, you can set
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<TT
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CLASS="LITERAL"
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>os_type</TT
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> to "NT".</P
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><P
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>Some older systems may not have both SRM and ARC in firmware as
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shipped. On these systems, you will have to upgrade your firmware.
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See <A
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HREF="http://ftp.digital.com/pub/DEC/Alpha/firmware/"
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TARGET="_top"
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>http://ftp.digital.com/pub/DEC/Alpha/firmware</A
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> for the
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latest firmware updates and instructions.</P
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><P
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>A few older systems (primarily evaluation boards such as the 164SX
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and 164LX) are "half-flash" systems, whose firmware can hold SRM or
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AlphaBIOS, but not both. If you have one of these machines, you will
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have to reflash your firmware with the SRM console using the AlphaBIOS
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firmware update utility. Again, see
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<A
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HREF="http://ftp.digital.com/pub/DEC/Alpha/firmware/"
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TARGET="_top"
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>http://ftp.digital.com/pub/DEC/Alpha/firmware</A
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> for firmware
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images and instructions. If you wish to return to AlphaBIOS on these
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machines, you may rerun the firmware update utility from a floppy in
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SRM using the <TT
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CLASS="LITERAL"
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>fwupdate</TT
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> command. You can also start AlphaBIOS
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from a floppy using the <TT
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CLASS="LITERAL"
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>arc</TT
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> command.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="AEN48"
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>2.2. Using the SRM console</A
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></H2
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><P
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>The SRM console works very much like a Unix or OpenVMS shell. It
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views your NVRAM and devices as a pseudo-filesystem. You can see this
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if you use the <TT
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CLASS="LITERAL"
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>ls</TT
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> command. Also, it contains a fairly large set
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of diagnostic, setup, and debugging utilities, the details of which
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are beyond the scope of this document. As in the Unix shell, you can
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pipe the output of one command to the input of another, and there is a
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<TT
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CLASS="LITERAL"
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>more</TT
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> command that works not unlike the Unix one. To get a full
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listing of available commands, run:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>>>> help | more</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>As well, SRM has environment variables, a number of which are
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pre-defined and correspond to locations in NVRAM. You can view the
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entire list of environment variables and their values with the
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<TT
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CLASS="LITERAL"
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>show</TT
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> command (there are quite a few of them, so you will probably
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want to pipe its output to <TT
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CLASS="LITERAL"
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>more</TT
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>). You can also show variables
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matching a "glob" pattern - for example, <TT
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CLASS="LITERAL"
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>show boot*</TT
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> will show all
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the variables starting in "boot".</P
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><P
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>Environment variables are categorized as either <I
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CLASS="EMPHASIS"
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>read-only</I
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>,
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<I
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CLASS="EMPHASIS"
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>warm non-volatile</I
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>, or <I
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CLASS="EMPHASIS"
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>cold non-volatile</I
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>. The full listing
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of pre-defined variables is detailed in the Alpha Architecture
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Reference Manual. The most useful pre-defined environment variables
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for the purposes of booting Linux are <TT
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CLASS="LITERAL"
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>bootdef_dev</TT
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>,
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<TT
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CLASS="LITERAL"
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>boot_file</TT
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>, <TT
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CLASS="LITERAL"
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>boot_flags</TT
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>, and
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<TT
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CLASS="LITERAL"
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>auto_action</TT
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>, all of which are cold non-volatile.</P
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><P
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>To set environment variables, use the <TT
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CLASS="LITERAL"
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>set</TT
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> command, like this:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>>>> set bootdef_def dka0</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>If you set an undefined variable, it will be created for you, however
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it will not persist across reboots.</P
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><P
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>The <TT
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CLASS="LITERAL"
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>bootdef_dev</TT
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> variable specifies the device (using
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VMS naming conventions - see <A
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HREF="aboot.html#DEVICE-NAMING"
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>Section 5.6.1</A
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> for an
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explanation of these) which will be booted from if no device is
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specified on the <TT
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CLASS="LITERAL"
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>boot</TT
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> command line, or in an automatic boot.
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The <TT
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CLASS="LITERAL"
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>boot_file</TT
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> variable contains the filename to be
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loaded by the secondary bootloader, while <TT
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CLASS="LITERAL"
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>boot_flags</TT
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>
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contains any extra flags. <TT
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CLASS="LITERAL"
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>auto_action</TT
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> specifies the
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action which the console should take on power-up. By default, it is
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set to <TT
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CLASS="LITERAL"
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>HALT</TT
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>, meaning that the machine will start up in the
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SRM console. Once you have configured your bootloader and the
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boot-related variables, you can set it to <TT
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CLASS="LITERAL"
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>BOOT</TT
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> in order to
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boot automatically on power-up.</P
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><P
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>Finally, two helpful console keystrokes you should know are
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Control-C, which, as in the shell, halts a command in progress (such
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as an automatic boot), and Control-P, which if issued from the aboot
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prompt (or other secondary bootloader) will halt the bootloader and
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return you to the SRM console.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="HOW-SRM-BOOTS"
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>2.3. How Does SRM Boot an OS?</A
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></H2
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><P
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>All versions of SRM can boot from SCSI disks and the versions for
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recent platforms, such as the Noname or AlphaStations can boot from
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floppy disks as well. Network booting via <TT
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CLASS="LITERAL"
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>bootp</TT
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> is supported.
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Note that older SRM versions (notably the one for the Jensen)
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cannot boot from floppy disks. Booting from IDE devices
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is supported on newer platforms ( 164SX, 164LX, 164UX, DS20, DS10, DP264, UP2000(+), UP1000, UP1100 etc..). </P
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><P
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>Booting Linux with SRM is a two step process: first, SRM loads and
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transfers control to the secondary bootstrap loader. Then the
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secondary bootstrap loader sets up the environment for Linux, reads
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the kernel image from a disk filesystem and finally transfers control to Linux.</P
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><P
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>Currently, there are two secondary bootstrap loaders for Linux:
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the <I
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CLASS="EMPHASIS"
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>raw</I
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> loader that comes with the Linux kernel and <TT
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CLASS="LITERAL"
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>aboot</TT
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>
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which is distributed separately. These two loaders are described in
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more detail below.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="AEN88"
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>2.4. Loading The Secondary Bootstrap Loader</A
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></H2
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><P
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>SRM knows nothing about filesystems or disk-partitions. It simply
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expects that the secondary bootstrap loader occupies a consecutive
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range of physical disk sector, starting from a given offset. The
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information on the size of the secondary bootstrap loader and the
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offset of its first disk sector is stored in the first 512 byte
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sector. Specifically, the long integer at offset 480 stores the
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<I
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CLASS="EMPHASIS"
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>size</I
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> of the secondary bootstrap loader (in 512-byte blocks) and
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the long at offset 488 gives the <I
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CLASS="EMPHASIS"
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>sector number</I
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> at which the
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secondary bootstrap loader starts. The first sector also stores a
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flag-word at offset 496 which is always 0 and a checksum at offset
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504. The checksum is simply the sum of the first 63 long integers in
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the first sector.</P
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><P
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>If the checksum in the first sector is correct, SRM goes ahead and
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reads the <I
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CLASS="EMPHASIS"
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>size</I
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> sectors starting from the sector given in the
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<I
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CLASS="EMPHASIS"
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>sector number</I
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> field and places them in <I
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CLASS="EMPHASIS"
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>virtual</I
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> memory at
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address <TT
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CLASS="LITERAL"
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>0x20000000</TT
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>. If the reading completes successfully,
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SRM performs a jump to address <TT
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CLASS="LITERAL"
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>0x20000000</TT
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>.</P
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></DIV
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>About this manual</TD
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><TD
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> </TD
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>SRM Device Naming</TD
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