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1.1 root 1: Slimline Open Firmware - SLOF
2:
3: Copyright (C) 2004, 2008 IBM Corporation
4:
5:
6: Index
7: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
8: 1.0 Introduction to Open Firmware
9: 1.1 Build process
10: 2.0 Extension
11: 3.0 Limitations
12:
13: 1.0 Introduction to Open Firmware
14: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
15:
16: The IEEE Standard 1275-1994 [1], Standard for Boot (Initialization Configuration)
17: Firmware, Core Requirements and Practices, is the first non-proprietary open
18: standard for boot firmware that is usable on different processors and buses.
19: Firmware which complies with this standard (also known as Open Firmware)
20: includes a processor-independent device interface that allows add-in devices
21: to identify itself and to supply a single boot driver that can be used,
22: unchanged, on any CPU. In addition, Open Firmware includes a user interface
23: with powerful scripting and debugging support and a client interface that
24: allows an operating system and its loaders to use Open Firmware services
25: during the configuration and initialization process. Open Firmware stores
26: information about the hardware in a tree structure called the
27: ``device tree''. This device tree supports multiple interconnected system
28: buses and offers a framework for ``plug and play''-type auto configuration
29: across different buses. It was designed to support a variety of different
30: processor Instruction Set Architectures (ISAs) and buses.
31:
32: The full documentation of this Standard can be found in [1].
33:
34:
35: 1.1 Build process
36: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
37:
38: Open Firmware (OF) is based on the programming language Forth.
39: SLOF use Paflof as the Forth engine, which was developed by
40: Segher Boessenkool. Most parts of the Forth engine are implemented in
41: C, by using GNU extensions of ANSI C, (e.g. assigned goto, often misnamed "computed goto"),
42: resulting in a very efficient yet still quite portable engine.
43:
44: The basic Forth words, so-called primitives, are implemented with
45: a set of C macros. A set of .in and .code files are provided, which
46: define the semantic of the Forth primitives. A Perl script translates
47: these files into valid C code, which will be compiled into the Forth engine.
48: The complete Forth system composes of the basic Forth primitives and
49: a set of Forth words, which are compiled during the start of the Forth
50: system.
51:
52: Example:
53: Forth primitive 'dup'
54:
55: dup ( a -- a a) \ Duplicate top of stack element
56:
57:
58: prim.in:
59: cod(DUP)
60:
61: prim.code:
62: PRIM(DUP) cell x = TOS; PUSH; TOS = x; MIRP
63:
64: Generated code:
65:
66: static cell xt_DUP[] = { { .a = xt_DOTICK }, { .c = "\000\003DUP" },
67: { .a = &&code_DUP }, };
68:
69: code_DUP: { asm("#### " "DUP"); void *w = (cfa = (++ip)->a)->a;
70: cell x = (*dp); dp++; (*dp) = x; goto *w; }
71:
72: Without going into detail, it can be seen, that the data stack is
73: implemented in C as an array of cells, where dp is the pointer to the top of
74: stack.
75:
76: For the implementation of the Open Firmware, most of the
77: code is added as Forth code and bound to the engine. Also
78: the system vector for reset and all kinds of exceptions
79: will be part of the image. Additionally a secondary boot-loader
80: or any other client application can be bound to the code as payload,
81: e.g. diagnostics and test programs.
82:
83: The Open Firmware image will be put together by the build
84: process, with a loader at the start of the image. This loader
85: is called by Low Level Firmware and loads at boot time the Open
86: Firmware to it's location in memory (see 1.3 Load process). Additionally
87: a secondary boot loader or any other client application can be bound
88: to the code as payload.
89:
90: The Low Level Firmware (LLFW) is responsible for setting up the
91: system in an initial state. This task includes the setup of the
92: CPUs, the system memory and all the buses as well as the serial port
93: itself.
94:
95:
96: 2.0 Extension
97: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
98:
99: In the following paragraphs it will be shown how to add
100: new primitive words (i.e., words implemented not by building
101: pre-existing Forth words together, but instead implemented in
102: C or assembler). With this, it is possible to adapt SLOF to
103: the specific needs of different hardware and architectures.
104:
105:
106: To add primitives:
107:
108: For a new primitive, following steps have to be done:
109:
110: + Definition of primitive name in <arch>.in
111: - cod(ABC) defines primitive ABC
112:
113: You can also use the following in a .in file, see existing
114: code for how to use these:
115: - con(ABC) defines constant ABC
116: - col(ABC) defines colon definition ABC
117: - dfr(ABC) defines defer definition ABC
118:
119: + Definition of the primitives effects in <arch>.code
120: - PRIM(ABC) ... MIRP
121:
122: The code for the primitive body is any C-code. With
123: the macros of prim.code the data and return stack of
124: the Forth engine can be appropriately manipulated.
125:
126:
127: 3.0 Limitations of this package
128: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
129:
130: On a JS20 the memory setup is very static and therefore there are
131: only very few combinations of memory DIMM placement actually work.
132:
133: Known booting configurations:
134:
135: * 4x 256 MB (filling all slots) -- only "0.5 GB" reported.
136: * 2x 1 GB, slots 3/4 -- only "0.5 GB" reported.
137:
138: Known failing configurations
139:
140: * 2x 256 MB, slots 3/4
141: * 2x 256 MB, slots 1/2
142:
143: On a JS20 SLOF wil always report 0.5 GB even if there is much more memory
144: available.
145:
146: On a JS21 all memory configurations should work.
147:
148: Documentation
149: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
150:
151: [1] IEEE 1275-1994 Standard, Standard for Boot (Initialization Configuration)
152: Firmware: Core Requierements and Practices
153:
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