Livt.Bus

src/bridges/WishboneToAxi4LiteBridge32.lvt

namespace Livt.Bus.Bridges

using Livt.Bus.Axi4Lite
using Livt.Bus.Wishbone

/**
 * Converts Wishbone Classic cycles into AXI4-Lite transactions.
 * The ACK-only Wishbone profile cannot carry AXI error responses, so the most
 * recent downstream status remains available through LastResponse().
 */
component WishboneToAxi4LiteBridge32 : IAxi4Lite32Master
{
	// Response recorded before a transaction or when AXI completes normally.
	public const RESPONSE_OKAY: Logic[2] = 0b00

	// Response recorded when a downstream AXI handshake stage times out.
	public const RESPONSE_SLVERR: Logic[2] = 0b10

	// Wishbone source connected to the upstream side of this bridge.
	upstream: IWishbone32Master

	// Maximum ticks to wait for each downstream AXI handshake stage.
	timeoutTicks: uint

	// Most recent AXI response, or RESPONSE_SLVERR after a timeout.
	lastResponse: Logic[2]

	// True only when the most recent downstream transaction timed out.
	lastTimedOut: bool

	// True while a timed-out AXI transaction is being completed and discarded.
	recovering: bool

	/**
	 * Connects a Wishbone source and initializes the AXI4-Lite master outputs.
	 * The default timeout for each AXI handshake stage is 1 ms.
	 */
	new(upstream: flip IWishbone32Master)
	{
		this.upstream = upstream
		this.upstream.datout = 0x00000000
		this.upstream.ack = 0b0
		this.awaddr = 0x00000000
		this.awprot = 0b000
		this.awvalid = 0b0
		this.wdata = 0x00000000
		this.wstrb = 0b0000
		this.wvalid = 0b0
		this.bready = 0b0
		this.araddr = 0x00000000
		this.arprot = 0b000
		this.arvalid = 0b0
		this.rready = 0b0
		this.timeoutTicks = this.context.TicksFor(1ms)
		this.lastResponse = RESPONSE_OKAY
		this.lastTimedOut = false
		this.recovering = false
	}

	/**
	 * Sets the maximum ticks to wait for each downstream AXI handshake stage.
	 * The count is exact; zero times out on the first stalled evaluation.
	 * On timeout the bridge withholds ack so the Wishbone source can time out.
	 */
	public fn SetTimeoutTicks(timeoutTicks: uint)
	{
		this.timeoutTicks = timeoutTicks
	}

	/**
	 * Returns the maximum ticks allowed for each downstream AXI handshake stage.
	 */
	public fn GetTimeoutTicks() uint
	{
		return timeoutTicks
	}

	/**
	 * Returns the most recent AXI response.
	 * A downstream timeout is reported as RESPONSE_SLVERR.
	 */
	public fn LastResponse() Logic[2]
	{
		return lastResponse
	}

	/**
	 * Returns true when the most recent downstream AXI transaction timed out.
	 */
	public fn LastTimedOut() bool
	{
		return lastTimedOut
	}

	/**
	 * Returns true while the bridge drains a timed-out AXI transaction.
	 * New Wishbone cycles are ignored until recovery completes.
	 */
	public fn IsRecovering() bool
	{
		return recovering
	}

	/**
	 * Converts each Wishbone cycle into AXI channel handshakes and returns ack
	 * only after the downstream response is accepted.
	 */
	process Run()
	{
		var addressAccepted: bool = false
		var dataAccepted: bool = false
		var elapsed: uint = 0

		state Idle {
			recovering = false
			this.upstream.ack = 0b0
			this.awvalid = 0b0
			this.wvalid = 0b0
			this.bready = 0b0
			this.arvalid = 0b0
			this.rready = 0b0

			if (this.upstream.cyc == 0b1 && this.upstream.stb == 0b1) {
				lastResponse = RESPONSE_OKAY
				lastTimedOut = false
				elapsed = 0

				if (this.upstream.we == 0b1) {
					this.awaddr = this.upstream.adr
					this.awprot = 0b000
					this.awvalid = 0b1
					this.wdata = this.upstream.datin
					this.wstrb = this.upstream.sel
					this.wvalid = 0b1
					addressAccepted = false
					dataAccepted = false
					goto WriteTransfer
				} else {
					this.araddr = this.upstream.adr
					this.arprot = 0b000
					this.arvalid = 0b1
					goto ReadAddress
				}
			} else {
				goto Idle
			}
		}

		state WriteTransfer {
			if (this.awready == 0b1) {
				addressAccepted = true
				this.awvalid = 0b0
			}

			if (this.wready == 0b1) {
				dataAccepted = true
				this.wvalid = 0b0
			}

			if (addressAccepted && dataAccepted) {
				this.bready = 0b1
				elapsed = 0
				goto WriteResponse
			} elif ((elapsed + 1) >= timeoutTicks) {
				lastResponse = RESPONSE_SLVERR
				lastTimedOut = true
				recovering = true
				goto RecoverWriteTransfer
			} else {
				elapsed = elapsed + 1
				goto WriteTransfer
			}
		}

		state WriteResponse {
			if (this.bvalid == 0b1) {
				this.bready = 0b0
				lastResponse = this.bresp
				this.upstream.ack = 0b1
				goto Acknowledge
			} elif ((elapsed + 1) >= timeoutTicks) {
				lastResponse = RESPONSE_SLVERR
				lastTimedOut = true
				recovering = true
				goto RecoverWriteResponse
			} else {
				elapsed = elapsed + 1
				goto WriteResponse
			}
		}

		state ReadAddress {
			if (this.arready == 0b1) {
				this.arvalid = 0b0
				this.rready = 0b1
				elapsed = 0
				goto ReadData
			} elif ((elapsed + 1) >= timeoutTicks) {
				lastResponse = RESPONSE_SLVERR
				lastTimedOut = true
				recovering = true
				goto RecoverReadAddress
			} else {
				elapsed = elapsed + 1
				goto ReadAddress
			}
		}

		state ReadData {
			if (this.rvalid == 0b1) {
				this.rready = 0b0
				this.upstream.datout = this.rdata
				lastResponse = this.rresp
				this.upstream.ack = 0b1
				goto Acknowledge
			} elif ((elapsed + 1) >= timeoutTicks) {
				lastResponse = RESPONSE_SLVERR
				lastTimedOut = true
				recovering = true
				goto RecoverReadData
			} else {
				elapsed = elapsed + 1
				goto ReadData
			}
		}

		state RecoverWriteTransfer {
			if (this.awready == 0b1) {
				addressAccepted = true
				this.awvalid = 0b0
			}

			if (this.wready == 0b1) {
				dataAccepted = true
				this.wvalid = 0b0
			}

			if (addressAccepted && dataAccepted) {
				this.bready = 0b1
				goto RecoverWriteResponse
			} else {
				goto RecoverWriteTransfer
			}
		}

		state RecoverWriteResponse {
			if (this.bvalid == 0b1) {
				this.bready = 0b0
				goto WaitForRelease
			} else {
				goto RecoverWriteResponse
			}
		}

		state RecoverReadAddress {
			if (this.arready == 0b1) {
				this.arvalid = 0b0
				this.rready = 0b1
				goto RecoverReadData
			} else {
				goto RecoverReadAddress
			}
		}

		state RecoverReadData {
			if (this.rvalid == 0b1) {
				this.rready = 0b0
				goto WaitForRelease
			} else {
				goto RecoverReadData
			}
		}

		state Acknowledge {
			if (this.upstream.cyc == 0b0 || this.upstream.stb == 0b0) {
				this.upstream.ack = 0b0
				goto Idle
			} else {
				goto Acknowledge
			}
		}

		state WaitForRelease {
			if (this.upstream.cyc == 0b0 || this.upstream.stb == 0b0) {
				recovering = false
				goto Idle
			} else {
				goto WaitForRelease
			}
		}
	}
}