1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
|
package vexriscv.demo
import spinal.core._
import vexriscv.plugin.Plugin
import vexriscv.{Stageable, DecoderService, VexRiscv}
//This plugin example will add a new instruction named SIMD_ADD which do the following :
//
//RD : Regfile Destination, RS : Regfile Source
//RD( 7 downto 0) = RS1( 7 downto 0) + RS2( 7 downto 0)
//RD(16 downto 8) = RS1(16 downto 8) + RS2(16 downto 8)
//RD(23 downto 16) = RS1(23 downto 16) + RS2(23 downto 16)
//RD(31 downto 24) = RS1(31 downto 24) + RS2(31 downto 24)
//
//Instruction encoding :
//0000011----------000-----0110011
// |RS2||RS1| |RD |
//
//Note : RS1, RS2, RD positions follow the RISC-V spec and are common for all instruction of the ISA
class SimdAddPlugin extends Plugin[VexRiscv]{
//Define the concept of IS_SIMD_ADD signals, which specify if the current instruction is destined for ths plugin
object IS_SIMD_ADD extends Stageable(Bool)
//Callback to setup the plugin and ask for different services
override def setup(pipeline: VexRiscv): Unit = {
import pipeline.config._
//Retrieve the DecoderService instance
val decoderService = pipeline.service(classOf[DecoderService])
//Specify the IS_SIMD_ADD default value when instruction are decoded
decoderService.addDefault(IS_SIMD_ADD, False)
//Specify the instruction decoding which should be applied when the instruction match the 'key' parttern
decoderService.add(
//Bit pattern of the new SIMD_ADD instruction
key = M"0000011----------000-----0110011",
//Decoding specification when the 'key' pattern is recognized in the instruction
List(
IS_SIMD_ADD -> True,
REGFILE_WRITE_VALID -> True, //Enable the register file write
BYPASSABLE_EXECUTE_STAGE -> True, //Notify the hazard management unit that the instruction result is already accessible in the EXECUTE stage (Bypass ready)
BYPASSABLE_MEMORY_STAGE -> True, //Same as above but for the memory stage
RS1_USE -> True, //Notify the hazard management unit that this instruction use the RS1 value
RS2_USE -> True //Same than above but for RS2.
)
)
}
override def build(pipeline: VexRiscv): Unit = {
import pipeline._
import pipeline.config._
//Add a new scope on the execute stage (used to give a name to signals)
execute plug new Area {
//Define some signals used internally to the plugin
val rs1 = execute.input(RS1).asUInt //32 bits UInt value of the regfile[RS1]
val rs2 = execute.input(RS2).asUInt
val rd = UInt(32 bits)
//Do some computation
rd(7 downto 0) := rs1(7 downto 0) + rs2(7 downto 0)
rd(16 downto 8) := rs1(16 downto 8) + rs2(16 downto 8)
rd(23 downto 16) := rs1(23 downto 16) + rs2(23 downto 16)
rd(31 downto 24) := rs1(31 downto 24) + rs2(31 downto 24)
//When the instruction is a SIMD_ADD one, then write the result into the register file data path.
when(execute.input(IS_SIMD_ADD)) {
execute.output(REGFILE_WRITE_DATA) := rd.asBits
}
}
}
}
|
