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[/] [eco32/] [trunk/] [doc/] [architecture.eco32e] - Rev 87
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Instruction Formats
-------------------
RRR (three register operands)
RRS (two registers and a signed half operand)
RRH (two registers and an unsigned half operand)
RHH (one register and a half operand, high-order 16 bits encoded)
RRB (two registers and a 16 bit signed offset operand)
J (no registers and a 26 bit signed offset operand)
JR (one register operand)
Instruction Set
---------------
Notation:
'r[n]' The bits representing 'r' are padded with zeroes
to the left (or zeroes are dropped from the left)
until a width of n bits is reached.
'a || b' The bits representing 'a' and 'b' are concatenated;
'a' occupies the more significant bits.
All numbers are given in decimal (base 10), except when prefixed
with "0x", which means they are given in hexadecimal (base 16).
ADD (add)
format: RRR
coding: 0x00[6] || rs1[5] || rs2[5] || rd[5] || 0[11]
assembler: add rd,rs1,rs2
example: add $1,$2,$3
operation: The contents of register rs2 are added to the contents
of register rs1. The result is stored into register rd.
Overflow is ignored.
ADDI (add immediate)
format: RRS
coding: 0x01[6] || rs1[5] || rd[5] || simm[16]
assembler: add rd,rs1,simm
example: add $1,$2,1234
operation: The sign-extended immediate constant simm is added to
the contents of register rs1. The result is stored into
register rd. Overflow is ignored.
SUB (subtract)
format: RRR
coding: 0x02[6] || rs1[5] || rs2[5] || rd[5] || 0[11]
assembler: sub rd,rs1,rs2
example: sub $1,$2,$3
operation: The contents of register rs2 are subtracted from the
contents of register rs1. The result is stored into
register rd. Overflow is ignored.
SUBI (subtract immediate)
format: RRS
coding: 0x03[6] || rs1[5] || rd[5] || simm[16]
assembler: sub rd,rs1,simm
example: add $1,$2,1234
operation: The sign-extended immediate constant simm is subtracted
from the contents of register rs1. The result is stored
into register rd. Overflow is ignored.
AND (logical and)
format: RRR
coding: 0x10[6] || rs1[5] || rs2[5] || rd[5] || 0[11]
assembler: and rd,rs1,rs2
example: and $1,$2,$3
operation: The contents of register rs2 are bitwise anded with the
contents of register rs1. The result is stored into
register rd.
ANDI (logical and immediate)
format: RRH
coding: 0x11[6] || rs1[5] || rd[5] || uimm[16]
assembler: and rd,rs1,uimm
example: and $1,$2,1234
operation: The zero-extended immediate constant uimm is bitwise
anded with the contents of register rs1. The result
is stored into register rd.
OR (logical or)
format: RRR
coding: 0x12[6] || rs1[5] || rs2[5] || rd[5] || 0[11]
assembler: or rd,rs1,rs2
example: or $1,$2,$3
operation: The contents of register rs2 are bitwise ored with the
contents of register rs1. The result is stored into
register rd.
ORI (logical or immediate)
format: RRH
coding: 0x13[6] || rs1[5] || rd[5] || uimm[16]
assembler: or rd,rs1,uimm
example: or $1,$2,1234
operation: The zero-extended immediate constant uimm is bitwise
ored with the contents of register rs1. The result
is stored into register rd.
XOR (logical xor)
format: RRR
coding: 0x14[6] || rs1[5] || rs2[5] || rd[5] || 0[11]
assembler: xor rd,rs1,rs2
example: xor $1,$2,$3
operation: The contents of register rs2 are bitwise xored with the
contents of register rs1. The result is stored into
register rd.
Remark: (a xor b) <=> ((a and ~b) or (~a and b))
XORI (logical xor immediate)
format: RRH
coding: 0x15[6] || rs1[5] || rd[5] || uimm[16]
assembler: xor rd,rs1,uimm
example: xor $1,$2,1234
operation: The zero-extended immediate constant uimm is bitwise
xored with the contents of register rs1. The result
is stored into register rd.
Remark: (a xor b) <=> ((a and ~b) or (~a and b))
XNOR (logical xnor)
format: RRR
coding: 0x16[6] || rs1[5] || rs2[5] || rd[5] || 0[11]
assembler: xnor rd,rs1,rs2
example: xnor $1,$2,$3
operation: The contents of register rs2 are bitwise xnored with the
contents of register rs1. The result is stored into
register rd.
Remark: (a xnor b) <=> ((a and b) or (~a and ~b))
XNORI (logical xnor immediate)
format: RRH
coding: 0x17[6] || rs1[5] || rd[5] || uimm[16]
assembler: xnor rd,rs1,uimm
example: xnor $1,$2,1234
operation: The zero-extended immediate constant uimm is bitwise
xnored with the contents of register rs1. The result
is stored into register rd.
Remark: (a xnor b) <=> ((a and b) or (~a and ~b))
LDHI (load high immediate)
format: RHH
coding: 0x1F[6] || 0[5] || rd[5] || uimm[16]
assembler: ldhi rd,uimm
example: ldhi $1,1234
operation: The zero-extended immediate constant uimm is shifted
left by 16 bits. The result is stored into register rd.
BEQ (branch on equal)
format: RRB
coding: 0x20[6] || rs1[5] || rs2[5] || simm[16]
assembler: beq rs1,rs2,target
example: beq $1,$2,label3
operation: If the contents of register rs1 are equal to the contents
of register rs2, the sign-extended immediate constant
simm is shifted left by two bits and added to the address
of the instruction following the branch instruction. The
result is placed into the program counter. If the contents
differ, the next instruction after the branch is executed.
BNE (branch on not equal)
format: RRB
coding: 0x21[6] || rs1[5] || rs2[5] || simm[16]
assembler: bne rs1,rs2,target
example: bne $1,$2,label3
operation: If the contents of register rs1 are not equal to the contents
of register rs2, the sign-extended immediate constant
simm is shifted left by two bits and added to the address
of the instruction following the branch instruction. The
result is placed into the program counter. If the contents
are equal, the next instruction after the branch is executed.
BLEU (branch on less or equal unsigned)
format: RRB
coding: 0x23[6] || rs1[5] || rs2[5] || simm[16]
assembler: bleu rs1,rs2,target
example: bleu $1,$2,label3
operation: If the contents of register rs1 are less than or equal
to the contents of register rs2 (both are interpreted as
unsigned numbers), the sign-extended immediate constant
simm is shifted left by two bits and added to the address
of the instruction following the branch instruction. The
result is placed into the program counter. If the contents
do not satisfy the condition, the next instruction after
the branch is executed.
BLTU (branch on less than unsigned)
format: RRB
coding: 0x25[6] || rs1[5] || rs2[5] || simm[16]
assembler: bltu rs1,rs2,target
example: bltu $1,$2,label3
operation: If the contents of register rs1 are less than the contents
of register rs2 (both are interpreted as unsigned numbers),
the sign-extended immediate constant simm is shifted left
by two bits and added to the address of the instruction
following the branch instruction. The result is placed into
the program counter. If the contents do not satisfy the
condition, the next instruction after the branch is executed.
BGEU (branch on greater or equal unsigned)
format: RRB
coding: 0x27[6] || rs1[5] || rs2[5] || simm[16]
assembler: bgeu rs1,rs2,target
example: bgeu $1,$2,label3
operation: If the contents of register rs1 are greater than or equal
to the contents of register rs2 (both are interpreted as
unsigned numbers), the sign-extended immediate constant
simm is shifted left by two bits and added to the address
of the instruction following the branch instruction. The
result is placed into the program counter. If the contents
do not satisfy the condition, the next instruction after
the branch is executed.
BGTU (branch on greater than unsigned)
format: RRB
coding: 0x29[6] || rs1[5] || rs2[5] || simm[16]
assembler: bgtu rs1,rs2,target
example: bgtu $1,$2,label3
operation: If the contents of register rs1 are greater than the contents
of register rs2 (both are interpreted as unsigned numbers),
the sign-extended immediate constant simm is shifted left
by two bits and added to the address of the instruction
following the branch instruction. The result is placed into
the program counter. If the contents do not satisfy the
condition, the next instruction after the branch is executed.
J (jump)
format: J
coding: 0x2A[6] || simm[26]
assembler: j target
example: j label3
operation: The sign-extended immediate constant simm is shifted left
by two bits and added to the address of the instruction
following the jump instruction. The result is placed into
the program counter.
JR (jump register)
format: JR
coding: 0x2B[6] || rs[5] || 0[5] || 0[16]
assembler: jr rs
example: jr $31
operation: The contents of register rs are placed into the program
counter.
JAL (jump and link)
format: J
coding: 0x2C[6] || simm[26]
assembler: jal target
example: jal label3
operation: The address of the instruction following the jal instruction
is placed into register 31. The sign-extended immediate
constant simm is shifted left by two bits and added to the
address of the instruction following the jal instruction.
The result is placed into the program counter.
LDW (load word)
format: RRS
coding: 0x30[6] || rs[5] || rd[5] || simm[16]
assembler: ldw rd,rs,simm
example: ldw $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
A word is read from this address and stored into register
rd.
LDH (load halfword)
format: RRS
coding: 0x31[6] || rs[5] || rd[5] || simm[16]
assembler: ldh rd,rs,simm
example: ldh $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
A halfword is read from this address, sign-extended, and
stored into register rd.
LDHU (load halfword unsigned)
format: RRS
coding: 0x32[6] || rs[5] || rd[5] || simm[16]
assembler: ldhu rd,rs,simm
example: ldhu $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
A halfword is read from this address, zero-extended, and
stored into register rd.
LDB (load byte)
format: RRS
coding: 0x33[6] || rs[5] || rd[5] || simm[16]
assembler: ldb rd,rs,simm
example: ldb $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
A byte is read from this address, sign-extended, and stored
into register rd.
LDBU (load byte unsigned)
format: RRS
coding: 0x34[6] || rs[5] || rd[5] || simm[16]
assembler: ldbu rd,rs,simm
example: ldbu $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
A byte is read from this address, zero-extended, and stored
into register rd.
STW (store word)
format: RRS
coding: 0x35[6] || rs[5] || rd[5] || simm[16]
assembler: stw rd,rs,simm
example: stw $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
The contents of register rd (all 32 bits) are stored
as a word to this address.
STH (store halfword)
format: RRS
coding: 0x36[6] || rs[5] || rd[5] || simm[16]
assembler: sth rd,rs,simm
example: sth $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
The contents of register rd (the lower 16 bits) are stored
as a halfword to this address.
STB (store byte)
format: RRS
coding: 0x37[6] || rs[5] || rd[5] || simm[16]
assembler: stb rd,rs,simm
example: stb $1,$2,1234
operation: The sign-extended immediate constant simm is added to the
contents of register rs to form an effective memory address.
The contents of register rd (the lowest 8 bits) are stored
as a byte to this address.
Interrupts and Exceptions
-------------------------
There are neither interrupts nor exceptions in this version of ECO32e.
Unknown opcodes should nevertheless be recognized. A CPU simulation can
then report the execution of an unknown opcode; an implementation may
trap such an execution in a state of its controller which cannot be left
without reset.
Peripherals
-----------
Peripherals are memory-mapped. They need only support word accesses.
A sensible reaction to accesses with smaller widths (halfword or byte)
is not required.
In this version of ECO32e there are only two peripherals: a character
display and a keyboard.
The character display is capable of showing 30 lines with 80 characters
each. Its base address is 0x30100000. Each line occupies 128 words in
the I/O address space, one word for each column (and 48 unusable columns
at the end of the line). Therefore the address to which a character is
written and its location on the screen are related as follows:
address = 0x30100000 + (line * 128 + column) * 4
The character to be displayed must be written as a word to the corresponding
address with its ASCII code contained in the lowest 8 bits of the word.
The keyboard is represented by two I/O registers. The status register
is located at address 0x30200000. When read (32 bits), its LSB indicates
if a character has been received from the physical keyboard. If this bit
is 1, the character can be read at address 0x30200004, the address of
the data register. By reading this latter address, the LSB of the
status register is automatically reset to 0. The data register must be
read with a word read; the character read is contained in the lowest
8 bits of the word.
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