gmac infile.gm -o outfile.mem -l outfile.mapThis will read the description in "infile.gm", and generate the memory file "outfile.mem" and and the optional map file "outfile.map". The memory file will contain the appropriate "memory" keywords to load multiple memories. The map file contains the list of symbols defined in the input file in a human-readable form.
Gmac input files consist of a sequence of declarations. Whitespace and newlines are ignored, and comments are indicated by a '//'. A complete example of a Gmac input file is given in Appendix E.
The bit range [msb:lsb] specifies the portion of the word which will be stored at an address in the memory name. The specified memory should be the full path name of a memory in the circuit file. A word can be broken across multiple memories by using multiple bank statements. A single bank is limited to 32 bits, so memories with very long words, such as a micro-program will probably have to be broken into multiple memories. An optional address specifier after the memory name specifies the range of address which this memory will hold. If no address range is specified, this memory will be used for all words. As an example, consider the set of bank declarations:
microcode bank[31:0] iunit.m1; microcode bank[63:32] iunit.m2; map bank[7:0] iunit.map; macrocode bank[7:0] memory.m1;This indicates that the mirco-program will be consist of 64-bit instructions with the low half of the instructions being stored in "iunit.m1" and the high half of the instructions being stored in "iunit.m2". The map memory contains 8-bit data and is stored in "iunit.map". The main macrocode memory has 8-bit words and is stored in "memory.m1".
field cin[18], idata[9:2];declares that bit 18 of the microinstruction has the name "cin", and the bits 2 through 9 have the name "idata". Single bit fields can optionally be prepended with the "~" to indicate they are active low signals. A set of symbolic values can also be supplied for a field. For example:
field mpcop[1:0]={
next=0, // Increment mpc
reinit=1, // Restart CPU
jmap=2, // Jump from map value
jump=3 // Jump from condition
};
declares a 2-bit field "mpcop" with a set of symbolic names for field
values. Hexadecimal symbolic values can be specified by prepending them
with a "0x".
For each single-bit field, the presence of a field name in a microinstruction indicates that that bit should be asserted. For normal fields, this means setting the bit to 1 in the microinstruction. For active low fields (indicated with a "~" symbol in the field declaration) this means setting the bit to 0. The bit corresponding to any active low fields not specified in an instruction will be set to 1. For multi-bit fields, a value should be specified after an '=' symbol. The value can be either a fixed constant, a symbolic value defined for the field, or a label which will be resolved to the appropriate microinstruction address when the specification is compiled.
For example, consider the microcode fragment:
begin microcode @ 0 start: clq; // Q <- 0 idata=0x1 ALU_AZERO ALU_OP=add bop=idata ldqh; // Q.H <- 1 ALU_AZERO ALU_OP=add bop=qreg dout ldpc; // PC <- Q mpcop=jump mpccond=jmp mpcaddr=fetch; // jump to 'fetch' mpcop=next; endThis specifies that this fragment will begin at address 0. The first mirco instruction is labeled 'start' and simply asserts the signal 'clq'. In this case, this clears the contents of the Q register. The next micro-instruction puts the value '1' on the field name "idata", asserts the signal "ALU_AZERO", puts the symbolic value "add" on the field "ALU_IP", the symbolic value "idata" on the field "bop" and asserts the signal "ldqh". This set of operations causes a 1 to be stored in the high half of the Q register. The subsequent instructions load the program counter PC from the value stored in the Q register (0x100), and jumps to the label 'fetch'.
For example:
registers R0=0, R1=1, R2=2, R3=3, R4=4, R5=5, FP=6, SP=7;declares 8 registers name R0 through R5, FP and SP. With numeric values as specified in the declaration. The numeric value here will be used in building the macroinstruction using a register.
add R1,#1234 // register direct, immediate add R1,R2 // register direct, register direct add R1,(R2) // register direct, register indirect add R1,#Array(R3) // register direct, indexedWe can define the addressing mode combinations with the declaration:
operands myopts {
%1,#2 = { +0[1:0]=0; +1[7:4]=%1; +1[3:0]=0; +2=#2[7:0]; +3=#2[15:8]; };
%1,%2 = { +0[1:0]=1; +1[7:4]=%1; +1[3:0]=%2; };
%1,(%2) = { +0[1:0]=2; +1[7:4]=%1; +1[3:0]=0; +2=#2[7:0]; +3=#2[15:8]; };
%1,#2(%3) = { +0[1:0]=3; +1[7:4]=%1; +1[3:0]=%3; +2=#2[7:0]; +3=#2[15:8]; };
};
This block defines a set of 4 operand combinations for a two-operand
instruction. Each operand combination is specified by a comma
separated list of addressing modes. A '-' can be used in place of the
operand list to indicate instructions with no operands. Registers are
indicated by a '%' followed by an id number, and numbers are indicated
by a '#' followed by an id number. The statements in braces following
an address mode combination specify a sequence of assignments used to
build the macroinstruction. Each assignment contains a word number
within the macroinstruction, an optional bit range, and a value to
store at the specified location. If the value is a simple number, the
specified number will be stored. If the value is prepended with a '%'
or '#', then the value is taken to be the id number for a register or
number specified in the instruction. For example, on a machine with a
byte-addressable main memory, the previous operand declarations will
generate the bytes:
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ | undefined |1 1| |0 0 0 1|0 1 0 1| |0 0 1 1|1 0 0 0| |0 0 0 1|0 0 1 0| +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+for the instruction:
add R1, #0x1234(R5)Since the addressing modes are "register" and "indexed", the last entry in the list of operand combinations applies. The "+0[1:0]=3" statement sets the low two bits of the first byte to binary '11'. The "+1[7:4]=%1" statement sets the high half of the second bytes to the code for the R1 register, and the "+1[3:0]=%3" statement sets the low half of the second word to the code for the R5 register. The "+2=#2[7:0]" and "+3=#2[15:8]" statements store the index value '0x1234' in the third and fourth bytes of the instruction low byte first.
One last type of memory assignment is the relative address assignment. Relative addresses are indicated with the '@' operator. The pair of statements "+2=#2@[7:0]" and "+3=#2@[15:8]" will store the difference of the operand with id 2 and the address of the first byte of the instruction. This feature can be used to define relative branching instructions. An optional value can be specified after the '@' as a further fixed offset.
op add {
map add_ri : 0x68; // register direct, immediate
map add_rr : 0x69; // register direct, register direct
map add_rd : 0x6a; // register direct, register indirect
map add_rx : 0x6b; // register direct, indexed
+0[7:0]=0x68;
operands myopts;
};
defines the 'add' instruction with the operand set defined by myopts. The statement '+0[7:0]=0x68' defines the
base opcode for the instruction and the position to store it in the
instruction word. The 'map' statements define map memory values that
can be used to map an opcode to a microinstruction address. The left
side of the 'map' statement specifies a label in the microprogram.
The right side specifies an opcode value which maps to that address.
Since the low two bits of the first byte are used to indicate the
addressing mode, we need four map statements for each of the four
operand combinations. The map declarations shown here will cause the
map memory to contain the addresses for the microinstructions add_ri,
add_rr, add_rd and add_ri at the addresses 0x68, 0x69, 0x6a and 0x6b
in the map memory.
begin macrocode @ 0x100will start a block of macrocode at address 0x100. Unlike other portions of the gmac specification, newlines are significant in the macrocode block and indicate the end of a macroinstruction. A macro program consists of a list of instructions and directives. Any of the macroinstructions defined can be used, and labels can be defined by starting a line with an identifier followed by a ":".
| Directive | Description |
|---|---|
| label: .symbol value | Defines a label to be a specified value. |
| .short value, ... | Inserts a set of two-byte values at successive memory locations. |
| .long value, ... | Inserts a set of four-byte values at successive memory locations. |
| .byte value, ... | Inserts a set of byte values at successive memory locations. This directive can also take strings denoted by double quotes with each byte of the string being stored at successive locations. |
| .bss value | Reserves value bytes of unallocated memory at the current position. This directive can be used to define uninitialized global variables. |
| .proc label | This directive can be used in conjunction with ".end" to define a procedure. The label specified will be assigned the current address, but any labels defined between the ".proc" and the ".end" directives will be treated as local labels. |
| .end | Ends a procedure definition. |
begin macrocode @ 0x100 ttydata: .symbol 0x11 // tty data in/out register ttystatus: .symbol 0x10 // tty status register start: movw SP, 0 // Initialize the stack pointer to 0 movw FP, 0 // Initialize the frame pointer to 0 push msg // Push msg on the stack. call print // Call the procedure 'print' add SP,2 // Reset the stack pointer. sdone: jmp sdone // Hang in an infinate loop. //////////////////// // print(s) Print the string s // .proc print movw R1, 4(FP) // Store the argument value in R1 loop: movb R2, (R1) // Store the byte addressed by R1 in R2 jeq done // If the byte was a zero, jump to 'done' movb (ttydata),R2 // Store the byte in the tty data register movb (ttystatus),#1 // Write a 1 to the tty status register to output the byte add R1, #1 // Add 1 to the R1 register jmp loop // Jump back to 'loop' to get the next byte. done: ret .end msg: .byte "Hello World.\n", 0Given the appropriate circuit, mircrocode and macrocode definitions, this program will print the message "Hello World." on a tty and halt by entering an infinite loop.