synth_intel_alm: alternative synthesis for Intel FPGAs

By operating at a layer of abstraction over the rather clumsy Intel primitives,
we can avoid special hacks like `dffinit -highlow` in favour of simple techmapping.

This also makes the primitives much easier to manipulate, and more descriptive
(no more cyclonev_lcell_comb to mean anything from a LUT2 to a LUT6).

techlibs/intel_alm/common/dff_sim.v

@@ -0,0 +1,48 @@
+// DATAIN: synchronous data input
+// CLK: clock input (positive edge)
+// ACLR: asynchronous clear (negative-true)
+// ENA: clock-enable
+// SCLR: synchronous clear
+// SLOAD: synchronous load
+// SDATA: synchronous load data
+//
+// Q: data output
+//
+// Note: the DFFEAS primitive is mostly emulated; it does not reflect what the hardware implements.
+module MISTRAL_FF(
+    input DATAIN, CLK, ACLR, ENA, SCLR, SLOAD, SDATA,
+    output reg Q
+);
+
+`ifdef cyclonev
+specify
+    (posedge CLK => (Q : DATAIN)) = 262;
+    $setup(DATAIN, posedge CLK, 522);
+endspecify
+`endif
+`ifdef cyclone10gx
+specify
+    (posedge CLK => (Q : DATAIN)) = 219;
+    $setup(DATAIN, posedge CLK, 268);
+endspecify
+`endif
+
+initial begin
+    // Altera flops initialise to zero.
+	Q = 0;
+end
+
+always @(posedge CLK, negedge ACLR) begin
+    // Asynchronous clear
+    if (!ACLR) Q <= 0;
+    // Clock-enable
+	else if (ENA) begin
+        // Synchronous clear
+        if (SCLR) Q <= 0;
+        // Synchronous load
+        else if (SLOAD) Q <= SDATA;
+        else Q <= DATAIN;
+    end
+end
+
+endmodule