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axi4 Fragmenter: align all output accesses

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We promised the output is aligned. Make good on that!
This commit is contained in:
Wesley W. Terpstra 2016-10-13 13:57:59 -07:00
parent 84be93f9f3
commit 19064e602b
1 changed files with 10 additions and 6 deletions
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16
src/main/scala/uncore/axi4/Fragmenter.scala
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@ -96,19 +96,17 @@ class AXI4Fragmenter(lite: Boolean = false, maxInFlight: Int = 32, combinational
// Things that cause us to degenerate to a single beat
val fixed = a.bits.burst === AXI4Parameters.BURST_FIXED
val narrow = a.bits.size =/= UInt(lgBytes)
val misaligned = lo =/= UInt(0)
val bad = fixed || narrow || misaligned
val bad = fixed || narrow
// The number of beats-1 to execute
val beats1 = Mux(bad, UInt(0), maxSupported1)
val beats = ~(~(beats1 << 1 | UInt(1)) | beats1) // beats1 + 1
val inc_addr = addr + (beats << a.bits.size) // address after adding transfer
val align_addr = ~(~inc_addr | UIntToOH1(a.bits.size, lgBytes)) // AXI4 increments misaligned heads to aligned
val wrapMask = ~(~a.bits.len << a.bits.size) // only these bits may change, if wrapping
val mux_addr = Wire(init = align_addr)
val mux_addr = Wire(init = inc_addr)
when (a.bits.burst === AXI4Parameters.BURST_WRAP) {
mux_addr := (align_addr & wrapMask) | ~(~a.bits.addr | wrapMask)
mux_addr := (inc_addr & wrapMask) | ~(~a.bits.addr | wrapMask)
}
when (a.bits.burst === AXI4Parameters.BURST_FIXED) {
mux_addr := a.bits.addr
@ -119,9 +117,15 @@ class AXI4Fragmenter(lite: Boolean = false, maxInFlight: Int = 32, combinational
out.valid := a.valid
out.bits := a.bits
out.bits.addr := addr
out.bits.len := beats1
// We forcibly align every access. If the first beat was misaligned, the strb bits
// for the lower addresses must not have been set. Therefore, rounding the address
// down is harmless. We can do this after the address update algorithm, because the
// incremented values will be rounded down the same way. Furthermore, a subword
// offset cannot cause a premature wrap-around.
out.bits.addr := ~(~addr | UIntToOH1(a.bits.size, lgBytes))
when (out.fire()) {
busy := !last
r_addr := mux_addr