Binary Relocatable Format

BRF code is a stream of eight-bit bytes and can be stored on any data medium (tape, file etc). The information can be divided into the following three basic types:

• Control information: A single byte, the control number. This is interpreted as a linker command.

• Programmed information: Two bytes containing a 16-bit word, called a P-group

• Symbolic information in either four bytes for MAC or NPL, or six bytes for BRF produced by compilers (e.g. FORTRAN). This is called an S-group and contains a symbol of one to seven packed six-bit characters.

BRF code are sequences of BRF groups, where each BRF group is a a combination of the three basic types. A BRF group can take one of the following four forms:

 <control number byte>
 <control number byte><P-group><P-group>
 <control number byte><S-group>
 <control number byte><S-group><P-group>

BRF Control Numbers

The possible values and meaning of the control numbers are described in the following table. 'Words' are 16-bits words in big endian format.

Binary control numbers

Control Number	Mnemonic	Argument size in words	Interpretation
08	FEED	0	Ignored
18	LF	1	W1 -> ((CLC)), (CLC)+1 -> (CLC)
28	LR	1	W1+(PB) -> ((CLC)),(CLC)+1 -> (CLC)
38	LC	1	W1+(CDB) -> ((CLC)),(CLC)+1 -> (CLC)
48	AFF	2	W1+(W2)->(W2)
58	ARF	2	W1+(PB)+(W2) -> (W2)
68	AFR	2	W1+(W2+(PB)) -> (W2+(PB))
78	ARR	2	W1+(PB)+(W2+(PB)) -> (W2+(PB))
108	SFL	1	W1 -> (CLC)
118	AFL	1	W1+(CLC) -> (CLC), fill zeroes
128	SRL	1	W1+(PB) -> (CLC)
138		-	Not used
148	MAIN	2 (3)	Symbol in S-group will become the main entry. Size of S-group depends on LONG control number.
158	LIBR	2 (3)	Symbol in S-group will be conditionally loaded
168	ENTR	2 (3)	Symbol in the S-group is assigned value of CLC
178	BEG	0	(CLC) -> (PB) First control byte of a unit. Linker-managed counters reset.
208	REF	2 (3)	Symbol in S-group is referenced in CLC
218	END	1	W1 contains the BRF checksum
228	INHB	1	Warns that compilation errors have occured
238	EOF	0	End of loading
248	LNF	1+W1	W2,W3....,Wn -> (CLC),....,(CLC+W1-1)
258	RT	1	W1 contains real time priority
268	ASF	3 (4)	<symbol>,<number> Defines common length. Value of symbol in loader table = common start address.
278	ADS	2 (3)	<symbol> + (CLC-1) -> (CLC-1) Adds common address
308	MSG	1+W1	W1 contains length of message in words: W1 is followed by W1*2 ASCII character bytes
318		-	Not used
328	LONG	0	Flags a six-byte S-group (see MAIN,LIBR,ENTR,REF,ASF,ADS,INC,DBC,RLC,CXC)
338		-	Not used
348	INL	2	W2 -> (W1+(PB))
358	DBL	3	Wi -> (W1+(BP)+i-2) (i = 2 to 3)
368	RLL	4	Wi -> (W1+(PB)+i-2) (i = 2 to 4)
378	CLX	7	Wi -> (W1+(PB)+i-2) (i = 2 to 7)
408 *	INC	4 (5)	W5 -> (W4 + ADR)
418 *	DBC	5 (6)	Wi -> (W4 + ADR + i-5) (i = 5 to 6)
428 *	RLC	6 (7)	Wi -> (W4 + ADR + i-5) (i = 5 to 7)
438 *	CXC	9 (10)	Wi -> W4 + ADR + i-5) (i = 5 to 10)
448	BYL	2	W2(bit 0-7) -> (W1+(PB))(bit 0-7) if W2 bit 15=1 **
			W2(bit 0-7) -> (W1+(PB))(bit 8-15) if W2 bit 15=0 **
458 *	BYC	5	W5(bit 0-7) -> (W4+(ADR))(bit 0-7) if W5 bit 15=1 **
			W5(bit 0-7) -> (W4+(ADR))(bit 8-15) if W5 bit 15=0 **
468	NWL	1	W1 contains line number. (Not in use.)
478	DBG	0	Indicates start/stop of Debug information
508	PMO	0	Indicates start of program bank mode
518	DMO	0	Indicates start of data bank mode
528	LRP	1	Same as LR but PB of program bank
538	LRD	1	Same as LR but PB of data bank
548	DIC	-	Dictionary table follows. Each element contains name (3 words) and byte pointer (2 words). End of table marked by -1
* The W1, W2, and W3 contains a common block name. At load time the symbol must be defined. Its value is referred to as ADR.
** The documentation says the opposite (bit 0-7 if bit 15=0), but the documentation appears to be incorrect here.

BRF decoding example

The BRF Linker can also be used to inspect BRF code. The example below shows how to look at a single library function, "5STOP" (an internal Fortran function) from the Fortran-100 2-bank library file FORTRAN-2BANK:BRF. The BRF Linker command LIST-BRF-CODE is used to show the library entry. The columns are interpreted as follows:

1. Current location counter (octal)
2. BRF control number (octal)
3. BRF control number mnemonic
4. Either:
   • Symbolic names (LIBR, ENTR, MAIN etc.), or
   • Binary information (octal)
5. Disassembled instruction (if program mode, e.g. set by PMO)
6. Other values (octal), if relevant

- BRF Linker -  210721C01
Brl: list-brf-code
Input file :fortran-2bank
First unit :5stop
Last unit  :5stop
Output file:
     1     17 BEG  *** new BRF - unit ***
     1     32 LONG 
     1     51 DMO  
     1     15 LIBR 5STOP 
     1     50 PMO  
     1     16 ENTR 5STOP 
     1     24 LNF       3 
     1             146147 COPY SL DX
     2             135024 JPL I * 24
     3                  0 STZ *
     4     20 REF  5STACK 
     5     24 LNF      21 
     5                600 STZ ,B - 200
     6                  1 STZ * 1
     7                  0 STZ *
    10             146157 COPY SA DX
    11              46000 LDA ,X 0
    12               4606 STA ,B - 172
    13              46001 LDA ,X 1
    14               4607 STA ,B - 171
    15              44606 LDA ,B - 172
    16               4406 STA ,B 6
    17              44607 LDA ,B - 171
    20               4407 STA ,B 7
    21              44602 LDA ,B - 176
    22             172406 AAA 6
    23             171002 SAT 2
    24             135003 JPL I * 3
    25             135003 JPL I * 3
    26     20 REF  5INIT 
    27     20 REF  5MSTOP 
    30     20 REF  5LEAV 
    31     51 DMO  
     1     50 PMO  
    31      6 AFR       2,3
    31      6 AFR     210,20
    31      6 AFR     210,16
    31     51 DMO  
     1     50 PMO  
    31     21 END  checksum :  27512 
Brl: 

Note that the disassembled code may not be the final instruction as will be seen in the linked PROG file. In the example above the three AFR entries are used to modify the values of earlier fields (see AFR description in the table of control numbers). Here the location PB+3, which is 0+3, i.e. location counter 3 in the listing (0 STZ * is changed to 2, which is STZ * 2, and locations 20₈ and 16₈ are added with 210₈, resulting in instructions STA ,B - 161 and STA ,B - 162 respectively.

References

• Norsk Data Document ND–60.196.01 BRF-LINKER USER MANUAL Chapter 6