riscv/rocket-chip
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make external clock divider programmable

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This commit is contained in:
Andrew Waterman 2013-01-24 23:40:47 -08:00
parent c211d74e95
commit 1945fa898b
1 changed files with 35 additions and 12 deletions
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47
uncore/src/slowio.scala
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@ -3,7 +3,7 @@ package uncore
import Chisel._ import Chisel._
import Constants._ import Constants._
class slowIO[T <: Data](val divisor: Int, hold_cycles_in: Int = -1)(data: => T) extends Component class SlowIO[T <: Data](val divisor_max: Int)(data: => T) extends Component
{ {
val io = new Bundle { val io = new Bundle {
val out_fast = new FIFOIO()(data).flip val out_fast = new FIFOIO()(data).flip
@ -13,31 +13,54 @@ class slowIO[T <: Data](val divisor: Int, hold_cycles_in: Int = -1)(data: => T)
val in_slow = new FIFOIO()(data).flip val in_slow = new FIFOIO()(data).flip
val clk_slow = Bool(OUTPUT) val clk_slow = Bool(OUTPUT)
val set_divisor = new PipeIO()(Bits(width = 32)).flip
val divisor = Bits(OUTPUT, 32)
} }
val hold_cycles = if (hold_cycles_in == -1) divisor/4 else hold_cycles_in require(divisor_max >= 8 && divisor_max <= 65536 && isPow2(divisor_max))
require((divisor & (divisor-1)) == 0) val divisor = Reg(resetVal = UFix(divisor_max-1))
require(hold_cycles < divisor/2 && hold_cycles >= 1) val d_shadow = Reg(resetVal = UFix(divisor_max-1))
val hold = Reg(resetVal = UFix(divisor_max/4-1))
val h_shadow = Reg(resetVal = UFix(divisor_max/4-1))
when (io.set_divisor.valid) {
d_shadow := io.set_divisor.bits(log2Up(divisor_max)-1, 0).toUFix
h_shadow := io.set_divisor.bits(log2Up(divisor_max)-1+16, 16).toUFix
}
io.divisor := hold << UFix(16) | divisor
val cnt = Reg() { UFix(width = log2Up(divisor)) } val count = Reg{UFix(width = log2Up(divisor_max))}
cnt := cnt + UFix(1) val clock = Reg{Bool()}
val out_en = cnt === UFix(divisor/2+hold_cycles-1) // rising edge + hold time count := count + UFix(1)
val in_en = cnt === UFix(divisor/2-1) // rising edge
val rising = count === (divisor >> UFix(1))
val falling = count === divisor
val held = count === (divisor >> UFix(1)) + hold
when (falling) {
divisor := d_shadow
hold := h_shadow
count := UFix(0)
clock := Bool(false)
}
when (rising) {
clock := Bool(true)
}
val in_slow_rdy = Reg(resetVal = Bool(false)) val in_slow_rdy = Reg(resetVal = Bool(false))
val out_slow_val = Reg(resetVal = Bool(false)) val out_slow_val = Reg(resetVal = Bool(false))
val out_slow_bits = Reg() { data } val out_slow_bits = Reg() { data }
val fromhost_q = new Queue(1)(data) val fromhost_q = new Queue(1)(data)
fromhost_q.io.enq.valid := in_en && (io.in_slow.valid && in_slow_rdy || reset) fromhost_q.io.enq.valid := rising && (io.in_slow.valid && in_slow_rdy || reset)
fromhost_q.io.enq.bits := io.in_slow.bits fromhost_q.io.enq.bits := io.in_slow.bits
fromhost_q.io.deq <> io.in_fast fromhost_q.io.deq <> io.in_fast
val tohost_q = new Queue(1)(data) val tohost_q = new Queue(1)(data)
tohost_q.io.enq <> io.out_fast tohost_q.io.enq <> io.out_fast
tohost_q.io.deq.ready := in_en && io.out_slow.ready && out_slow_val tohost_q.io.deq.ready := rising && io.out_slow.ready && out_slow_val
when (out_en) { when (held) {
in_slow_rdy := fromhost_q.io.enq.ready in_slow_rdy := fromhost_q.io.enq.ready
out_slow_val := tohost_q.io.deq.valid out_slow_val := tohost_q.io.deq.valid
out_slow_bits := Mux(reset, fromhost_q.io.deq.bits, tohost_q.io.deq.bits) out_slow_bits := Mux(reset, fromhost_q.io.deq.bits, tohost_q.io.deq.bits)
@ -46,5 +69,5 @@ class slowIO[T <: Data](val divisor: Int, hold_cycles_in: Int = -1)(data: => T)
io.in_slow.ready := in_slow_rdy io.in_slow.ready := in_slow_rdy
io.out_slow.valid := out_slow_val io.out_slow.valid := out_slow_val
io.out_slow.bits := out_slow_bits io.out_slow.bits := out_slow_bits
io.clk_slow := cnt(log2Up(divisor)-1).toBool io.clk_slow := clock
} }