The lengths of the instructions longer than 32 bits are indicated by their first few bits as follows:
0111110110 96 bits 0111110111 160 bits 0111111 144 bits 11001 64 bits 1101 48 bits 11111 80 bits
The formats of the 48-bit instructions are shown below:
Lines 2 through 5 show an instruction format which includes a B bit, for break, which, if cleared, indicates the instruction may be performed in parallel with the one that preceded it, a P bit, for predicated, which indicates the instruction is predicated, and an S bit, for sense.
The flag field selects a flag bit; if the instruction is predicated,
it is performed if the flag bit is set when the S bit is 0,
but it is performed if the flag bit is cleared when the S bit is
1.
In addition to including a normal 32-bit instruction, this type of instruction may include a pair of short instructions. Each one may have a six-bit opcode field if it is an integer operation, or a five-bit opcode field if it is a floating-point operation.
In the case where both short instructions are of the same type, an additional break bit is provided to indicate, if clear, that the two short instructions within the 48-bit instruction may be performed in parallel. In line 4, there is space for this bit between the two floating-point instructions; in line 5, it is placed ahead of the pair of integer operations, but it still signifies a break between those two instructions.
In line 3 of the diagram, we see that when one is a floating-point operation, and the other is an integer operation, since the two operations use a different ALU and a different register bank, it is assumed that they may always be executed in parallel, and the break bit is not provided.
Note that among the memory reference instructions shown in lines 10 through 13, there are memory-to-register operate instructions, which is why a C bit is present.
The formats of 64-bit instructions are shown below: in these instructions,
the first five bits are 11001, to indicate that the instruction is 64 bits long.
The formats of 80-bit instructions are shown below: in these instructions,
the first five bits are 11111, to indicate that the instruction is 80 bits long.
Lines 2 through 5 of the diagram illustrate an instruction format similar to that shown in lines 2 through 5 of the diagram of 48-bit instructions. Here, the two embedded 32-bit instructions may not be predicated, but each one still has a break bit, and in addition, they may be replaced with paired short instructions, which under some circumstances have an additional break bit between the two short instructions of the pair, as noted for the 48-bit instructions.
The formats of the 96-bit, 144-bit, and 160-bit instructions are shown below; these are squeezed into a tiny bit of leftover opcode space at the end of the 32-bit operate instructions.
