
R DC
20.1
R8820LV Execution Timings
RISC DSP Controller
R8820LV
RDC Semiconductor Co.
Rev:1.0
Subject to change without notice
85
The above instruction timing represent the minimum execution time in clock cycles for each instruction. The timings given
are based on the following assumptions:
1. The opcode, along with and data or displacement required for execution, has been prefetched and resides in the instruction
queue at the time is needed.
2. No wait states or bus HOLDs occur.
3. All word -data is located on even-address boundaries.
4. One RISC micro operation(
u
OP) maps one cycle(according the pipeline stages described below) , except the following
case:
4.1
Memory read
u
OP need 6 cycles for bus.
4.2
Memory push
u
OP need 1 cycle if it has no previous
Memory push
u
OP, and 5 cycles if it has previous
Memory push
or
Memory Write u
OP.
4.3
MUL
u
OP and
DIV
of ALU function
u
OP for 8 bits operation need both 8 cycles, for 16 bits operation need both 16
cycles.
4.4 All jumps, calls, ret and loopXX instructions required to fetch the next instruction for the destination
address(
Unconditional Fetch
u
OP) will need 9 cycles.
Note
: op_r: operand read stage, EA: Calculate Effective Address stage, Idle: Bus Idle stage, T0..T3: Bus T0..T3 stage,
Access: Access data from cache memory stage.
Pipeline Stages for single micro operation(one cycle):
Fetch
à
Decode
à
op_r
à
ALU
à
WB
(For ALU function
u
OP)
Fetch
à
Decode
à
EA
à
Access
à
WB
(For Memory function
u
OP)
Pipeline stages for
Memory read
u
OP(6 cycles):
Fetch
à
Decode
à
EA
à
Access
à
Idle
à
T0
à
T1
à
T2
à
T3
à
WB
Bus Cycle
Pipeline stages for
Memory push
u
OP after
Memory push
u
OP (another 5 cycles):
Fetch
à
Decode
à
EA
à
Access
à
Idle
à
T0
à
T1
à
T2
à
T3
à
WB (1
st
Memory push
u
OP)
(2
nd
u
OP) Fetch
à
Decode
à
EA
à
Access
à
Access
à
Access
à
Access
à
Access
à
Idle
à
T0
à
T1
à
T2
à
T3
à
WB
pipeline stall
Pipeline stages for unconditional fetch:
Fetch
à
Decode
à
EA
à
Access
à
Idle
à
T0
à
T1
à
T2
à
T3
à
Fetch
(
Fetch u
OP)
(next
u
OP) Fetch
à
Decode
à
EA
à
Access
à
Access
à
Access
à
Access
à
Access
à
Idle
à
T0
à
T1
à
T2
à
T3
à
WB
will be flushed
These 9 cycles caused branch penalty
à
Fetch
à
Decode
à
following stages..
.
(New
u
OP)