gary/lib/ECP5_RAM.bsv

////////////////////////////////////////////////////////////
package ECP5_RAM;

import DReg::*;
import Printf::*;
import ToString::*;
import StmtFSM::*;

import DelayLine::*;

export EBRWriteMode(..);
export EBRPortConfig(..);
export EBRPort(..);
export EBR(..);
export mkEBRCore;
export mkEBR;

////////////////////////////////////////////////////////////
// Configuration types
//
// The exported block RAMs in this package have one or more ports,
// where each port is independently configurable. Not all parameters
// are exposed, notably reset behavior is hardcoded to synchronous
// reset and release. This is purely because I don't yet understand
// Bluespec's reset semantics well enough to be confident in exposing
// async reset without messing it up.
//
// The exported EBRPortConfig type is internally expanded into an
// EBRPortConfig_Resolved. This expansion process resolves defaults,
// (e.g. assigning a default clock if none was provided), derives some
// additional values that implementations need (e.g. the widths of the
// data and address I/Os as regular integers), and checks the
// configuration for consistency errors (e.g. an address type larger
// than what the hardware can support).

// EBRWriteMode specifies an EBR port's output for a write operation,
// if any.
typedef enum {
   // In Normal mode, write operations do not output a value.
   Normal,
   // In WriteThrough mode, write operations output the value that was
   // written.
   WriteThrough,
   // In ReadBeforeWrite mode, write operations output the value that
   // was overwritten. This mode is only available on 9-bit and 18-bit
   // EBR configurations.
   ReadBeforeWrite
} EBRWriteMode deriving (Bits, Eq);

// EBRPortConfig is the configuration of an EBR port.
typedef struct {
   // clk, if specified, is the Clock to use for the port. If
   // unspecified, uses the module's default clock.
   Maybe#(Clock) clk;
   // rstN, if specified, is the Reset to use for the port. If
   // unspecified, uses the module's default reset.
   Maybe#(Reset) rstN;
   // Whether to register the output of the EBR port.
   //
   // EBR ports always register their inputs, to present predictable
   // signals to the memory circuitry. Ports can optionally also
   // enable an output register, which adds latency to operations but
   // decouples the memory's internal latency from the logic connected
   // to the output. This may allow designs to run at higher clock
   // speeds, outweighing the added cycle overhead.
   //
   // With non-registered output, EBR operations have a latency of 1
   // cycle. Registering the output increases that to 2 cycles. By
   // default, the output is not registered.
   Bool register_output;
   // chip_select_addr is the port's chip select address. The port
   // ignores put operations that don't provide a matching chip_select
   // argument.
   //
   // This is intended to make it easier to construct larger memories
   // out of multiple EBR ports: by configuring different chip
   // addresses for each port, the inputs to the overall memory can be
   // routed directly to all EBR ports, rather than having to provide
   // your own address decoding and routing logic.
   UInt#(3) chip_select_addr;
   // write_mode specifies what the EBR port outputs for write
   // operations. In the default Normal mode, write operations do not
   // produce any output.
   EBRWriteMode write_mode;
} EBRPortConfig deriving (Eq);

instance DefaultValue#(EBRPortConfig);
   defaultValue = EBRPortConfig{
      clk: defaultValue,
      rstN: defaultValue,
      register_output: False,
      chip_select_addr: 0,
      write_mode: Normal
   };
endinstance

// EBRPortConfig_Resolved is an elaborated version of EBRPortConfig,
// with all defaults and overrides resolved to their concrete values,
// port widths made explicit and verified.
typedef struct {
   // These fields are the same as in EBRPortConfig. If the port is
   // not in use, they are tied to default values that avoid any logic
   // or wires being generated outside of the EBR.
   Clock clk;
   Reset rstN;
   Bool register_output;
   UInt#(3) chip_select_addr;
   EBRWriteMode write_mode;

   // These are values derived by resolvePortCfg from an EBRPortConfig
   // and other contextual information from a module
   // instantiation. These are values that modules need to derive, so
   // we derive them all once here instead of forcing each module to
   // do so.

   // enabled is whether the port is in use at all. Modules omit all
   // glue logic and wiring for disabled ports, resulting in zero
   // burden during synthesis (other than consuming an EBR primitive,
   // but presumably you're using the other port still).
   //
   // Enabled is true if the memory's type for values is a non-zero
   // number of bits. In particular, eanbled=False if the caller uses
   // 'void' as the port's data type.
   Bool enabled;
   // addr_width is the bit width of addresses. resolvePortCfg ensures
   // that it is less than or equal to the maximum address width that
   // makes sense for data_width.
   Integer addr_width;
   // data_width is the bit width of input and output values at the
   // primitive hardware layer. The data width exported from the
   // wrapper types can be narrower. This value is always one of the
   // valid values for the EBR primitive: 1, 2, 4, 9 or 18.
   Integer data_width;
   // write_outputs_data is whether write_mode is one of the modes
   // where write operations output a value. Modules use this to
   // generate the appropriate conditions for port reads.
   Bool write_outputs_data;
   // operation_latency is how many cycles elapse between put()
   // executing to read() being ready. It is used to generate the
   // appropriate conditions for port reads.
   //
   // Operation latency on enabled ports is 2 if the output is
   // registered, or 1 for unregistered output. Disabled ports have 0
   // latency, meaning no timing logic is needed.
   Integer operation_latency;
   // chip_select_addr_str is the string encoding of chip_select_addr
   // that the EBR hardware primitive wants for its configuration
   // parameter.
   String chip_select_addr_str;
   // write_mode_str is the string encoding of write_mode that hte EBR
   // hardware primitive wants for its configuration parameter.
   String write_mode_str;
   // register_output_str is the string encoding of register_output
   // that the EBR hardware primitive wants for its configuration
   // parameter.
   String register_output_str;
} EBRPortConfig_Resolved;

function EBRPortConfig_Resolved resolvePortCfg(String module_name, String port_name, addr a, data d, EBRPortConfig cfg, Clock defaultClk, Reset defaultRstN)
   provisos (Bits#(addr, addr_sz),
             Bits#(data, data_sz));
   let addr_sz = valueOf(addr_sz);
   let data_sz = valueOf(data_sz);

   let data_hw_sz = 0;
   if (data_sz > 18)
      data_hw_sz = error(sprintf("invalid data width %d for %s port %s, must be 0..18 bits",
                                 data_sz, module_name, port_name));
   else if (data_sz > 9) data_hw_sz = 18;
   else if (data_sz > 4) data_hw_sz = 9;
   else if (data_sz > 2) data_hw_sz = 4;
   else if (data_sz > 1) data_hw_sz = 2;
   else if (data_sz > 0) data_hw_sz = 1;

   let addr_max = case (data_hw_sz)
                     0: 0;
                     1: 14;
                     2: 13;
                     4: 12;
                     9: 11;
                     18: 10;
                     default: error("unreachable");
                  endcase;

   let enabled = data_hw_sz != 0;
   let ret = ?;
   if (enabled)
      ret = EBRPortConfig_Resolved{
         enabled: True,
         clk: cfg.clk matches tagged Valid .clk ? clk : defaultClk,
         rstN: cfg.rstN matches tagged Valid .rstN ? rstN : defaultRstN,
         addr_width: addr_sz,
         data_width: data_hw_sz,
         register_output: cfg.register_output,
         chip_select_addr: cfg.chip_select_addr,
         write_mode: cfg.write_mode,
         write_outputs_data: cfg.write_mode != Normal,
         operation_latency: cfg.register_output ? 2 : 1,
         chip_select_addr_str: sprintf("0b%03b", cfg.chip_select_addr),
         write_mode_str: case (cfg.write_mode) matches
                            Normal: "NORMAL";
                            WriteThrough: "WRITETHROUGH";
                            ReadBeforeWrite: "READBEFOREWRITE";
                         endcase,
         register_output_str: cfg.register_output ? "OUTREG": "NOREG"
      };
   else
      ret = EBRPortConfig_Resolved{
         enabled: False,
         clk: noClock,
         rstN: noReset,
         addr_width: 14,
         data_width: 18,
         register_output: False,
         chip_select_addr: 0,
         write_mode: Normal,
         write_outputs_data: False,
         operation_latency: 0,
         chip_select_addr_str: "0b000",
         write_mode_str: "NORMAL",
         register_output_str: "NOREG"
      };
   if (addr_sz > addr_max) begin
      addr dummy = ?;
      ret = error(sprintf("The address type for port %s of %s is wider than the hardware can implement. "+
                          "Address type %s has %d bits, maximum is %d",
                          port_name, module_name,
                          printType(typeOf(dummy)),
                          addr_sz,
                          addr_max));
   end
   return ret;
endfunction

////////////////////////////////////////////////////////////
// Exported interfaces
//

// EBRPort is a port of an EBR memory.
(* always_ready *)
interface EBRPort#(type addr, type data);
   method Action put(UInt#(3) chip_select, Bool write, addr address, data datain);
   method data read();
endinterface

// EBR is an EBR memory.
interface EBR#(type portA_addr, type portA_data, type portB_addr, type portB_data);
   interface EBRPort#(portA_addr, portA_data) portA;
   interface EBRPort#(portB_addr, portB_data) portB;
endinterface

////////////////////////////////////////////////////////////
// Verilog import
//
// The raw primitive for EBR is called DP16KD. However, Lattice and
// Yosys both expose it with the I/O ports exploded out into
// individual bit signals, which is pretty horrible to plumb up here.
//
// Instead, ECP5_RAM.v defines a tiny Verilog wrapper, whose only
// purpose is to group those individual bit signals back into
// multi-bit ports that Bluespec can manipulate more elegantly.
//
// This wrapper exposes all the I/O ports with their maximum bit
// width, even though there is no configuration that can use all the
// bits. For example if you use all 14 address bits, you're only using
// 1 data bit (16384x1b configuration). If you're using all 18 bits of
// data, you're only using 10 address bits (1024x18b
// configuration). We do this because we want to drive unused signals
// to defined values, so we have to be able to see all of them.
//
// The exported wrapper modules defined further down translate these
// large raw ports into proper Bluespec types, and handle the
// necessary padding and truncation.

(* always_ready *)
interface V_EBRPort;
   // Put starts an operation, if select's value matches the port's
   // configured chip_select_addr.
   method Action put(UInt#(3) select, Bool write, Bit#(14) address, Bit#(18) data);
   // Read provides the EBR's output value. At this raw layer, read
   // always returns a value, but that value is undefined unless a put
   // which generates output happened N cycles prior, where N is the
   // port's configured latency (see EBRPortConfig).
   //
   // It is the caller's responsibility to time reads correctly
   // relative to puts.
   method Bit#(18) read();
endinterface

interface V_EBR;
   interface V_EBRPort portA;
   interface V_EBRPort portB;
endinterface

// vEBRCoreInner instantiates a raw EBR primitive with the given
// configuration.
//
// The returned interface has maximally wide types on all I/O, and
// uses plain bit arrays. It also has no conditions on any methods,
// it's the caller's reponsibility to time method calls appropriately.
//
// Nothing should use this module directly, except for mkEBRCore
// below. mkEBRCore wraps the Verilog primitive in stronger types and
// handles configuration edge cases (detecting invalid configs, tying
// off unused ports), but otherwise presents the same "raw" primitive
// from a semantic perspective. Anything you can build using
// vMkEBRCore, you can build better with mkEBRCore.
import "BVI" ECP5_RAM =
   module vMkEBRCore#(EBRPortConfig_Resolved cfgA,
                      EBRPortConfig_Resolved cfgB)
      (V_EBR);

      // EBRs are dual-port with independent clocks and resets on each
      // port, so we need to be careful to map things correctly. Unset
      // the default clock and reset entirely, so that the compiler
      // complains loudly if we forget to explicitly specify the
      // clocking/reset on a signal.
      default_clock no_clock;
      default_reset no_reset;

      input_clock portA_clk(CLKA, (* unused *)CLKA_GATE)  = cfgA.clk;
      input_reset portA_rstN(RSTA) clocked_by(portA_clk) = cfgA.rstN;

      input_clock portB_clk(CLKB, (* unused *)CLKB_GATE)  = cfgB.clk;
      input_reset portB_rstN(RSTB) clocked_by(portB_clk) = cfgB.rstN;

      parameter DATA_WIDTH_A = cfgA.data_width;
      parameter REGMODE_A = cfgA.register_output ? "OUTREG" : "NOREG";
      parameter CSDECODE_A = cfgA.chip_select_addr_str;
      parameter WRITEMODE_A = cfgA.write_mode_str;

      parameter DATA_WIDTH_B = cfgB.data_width;
      parameter REGMODE_B = cfgB.register_output ? "OUTREG" : "NOREG";
      parameter CSDECODE_B = cfgB.chip_select_addr_str;
      parameter WRITEMODE_B = cfgB.write_mode_str;

      // The outputs of EBR ports also have an enable signal. It's
      // unclear why you'd want to suppress the output of things you
      // asked the memory to give you. Since I can't think of any use
      // for them, leave them always enabled if the corresponding port
      // is active.
      port OCEA = cfgA.enabled;
      port OCEB = cfgB.enabled;

      interface V_EBRPort portA;
         method put((*reg*)CSA, (*reg*)WEA, (*reg*)ADA, (*reg*)DIA) enable(CEA) clocked_by(portA_clk) reset_by(portA_rstN);
         method DOA read() clocked_by(portA_clk) reset_by(portA_rstN);
      endinterface
      interface V_EBRPort portB;
         method put((*reg*)CSB, (*reg*)WEB, (*reg*)ADB, (*reg*)DIB) enable(CEB) clocked_by(portB_clk) reset_by(portB_rstN);
         method DOB read() clocked_by(portB_clk) reset_by(portB_rstN);
      endinterface

      // A quick crash course on Bluespec's scheduling instructions.
      //
      // Bluespec's fundamental property is that rule execution is
      // serializable: all designs behave as if they execute a single
      // rule at a time, in some order. In the actual hardware
      // typically many rules execute in parallel on every cycle, but
      // that's just an optimization: the observed behavior of the
      // system must always be explainable by executing rules one at a
      // time, where each rule sees the effects of all previously
      // executed rules.
      //
      // When pulling Verilog modules into a Bluespec universe, the
      // compiler must be told explicitly what orders of execution are
      // valid, given the hardware's behavior. The canonical example
      // is a read of a register's value and a write to the same
      // register. Those two actions produce different system states
      // depending on which one executes first: if read-before-write,
      // the read sees the register's old value. In write-before-read,
      // the read sees the updated value.
      //
      // That's why, if you go digging into the low level Bluespec
      // definition of what a register is, you'll find a scheduling
      // annotation which says that if a read and a write both want to
      // happen (both methods are "enabled" in a clock cycle), the
      // read must execute before the write. When translated into
      // hardware, this matches familiar synchronous logic: on a given
      // cycle, your logic sees the previous cycle's value, and all
      // writes to registers happen at the "end" of the cycle.
      //
      // And so we come to the scheduling rules. Our annotations tell
      // the compiler how the memory's methods can be called, if
      // several of them are able to execute. Each scheduling
      // annotation is written as:
      //
      //   schedule <method(s) A> ORDERING <method(s) B>
      //
      // This means: assuming that method(s) A and method(s) B both
      // want both execute, can both be executed without issues? And
      // if yes, do they need to execute in a specific order?
      //
      // The orderings you can specify are:
      //
      //   - C : "conflict". The scheduler must pick a single one of A
      //         or B to execute.
      //   - CF : "conflict-free". A and B can both execute, and the
      //          outcome is the same regardless of which executes first.
      //   - SB : "schedule before". A and B can both execute, but A
      //          must execute first to get correct results.
      //   - SBR: "schedule before (restricted)". Same as SB, but A
      //          and B must also execute from different rules.
      //
      // With that, here are the scheduling annotations for
      // vMkEBRCore.

      // TODO: why is portA.read CF portA.put? Shouldn't that be SB to
      // match register semantics?
      schedule (portA.read) CF (portA.read);
      schedule (portA.read) SB (portA.put);
      schedule (portA.put) C (portA.put);
      schedule (portB.read) CF (portB.read);
      schedule (portB.read) SB (portB.put);
      schedule (portB.put) C (portB.put);
   endmodule : vMkEBRCore

////////////////////////////////////////////////////////////
// Exported modules

// mkEBRCore instantiates one EBR memory block with the given
// configuration.
//
// The returned ports have no implicit conditions. The caller is
// responsible for upholding the block's timing and synchronization
// requirements, following Lattice TN 02204.
//
// read() yields valid data 1 cycle after put() for ports configured
// with unregistered output, or 2 cycles for registered outputs. At
// all other times, the returned value is undefined.
//
// portA and portB must not concurrently write the same bits, or read
// bits while the other is writing them. The stored value in a
// write-write race is undefined, as is the read value in a write-read
// race.
module mkEBRCore#(EBRPortConfig cfgA,
                  EBRPortConfig cfgB)
   (EBR#(addr_a, data_a, addr_b, data_b))
   provisos (Bits#(addr_a, addr_sz_a),
             Bits#(data_a, data_sz_a),
             Bits#(addr_b, addr_sz_b),
             Bits#(data_b, data_sz_b),
             Add#(addr_a_pad, addr_sz_a, 14),
             Add#(data_a_pad, data_sz_a, 18),
             Add#(addr_b_pad, addr_sz_b, 14),
             Add#(data_b_pad, data_sz_b, 18));

   let defaultClk <- exposeCurrentClock;
   let defaultRstN <- exposeCurrentReset;
   let rcfgA = resolvePortCfg("mkEBRCore", "A", addr_a ' (?), data_a ' (?), cfgA, defaultClk, defaultRstN);
   let rcfgB = resolvePortCfg("mkEBRCore", "B", addr_b ' (?), data_b ' (?), cfgB, defaultClk, defaultRstN);

   let vEBR <- vMkEBRCore(rcfgA, rcfgB);

   interface EBRPort portA;
      method Action put(UInt#(3) chip_select, Bool write, addr_a address, data_a datain);
         if (!rcfgA.enabled)
            noAction;
         else
            vEBR.portA.put(chip_select, write, zeroExtend(pack(address)), zeroExtend(pack(datain)));
      endmethod
      method data_a read();
         if (!rcfgA.enabled)
            return ?;
         else
            return unpack(truncate(vEBR.portA.read()));
      endmethod
   endinterface

   interface EBRPort portB;
      method Action put(UInt#(3) chip_select, Bool write, addr_b address, data_b datain);
         if (!rcfgB.enabled)
            noAction;
         else
            vEBR.portB.put(chip_select, write, zeroExtend(pack(address)), zeroExtend(pack(datain)));
      endmethod
      method data_b read();
         if (!rcfgB.enabled)
            return ?;
         else
            return unpack(truncate(vEBR.portB.read()));
      endmethod
   endinterface
endmodule

// mkEBR instantiates one EBR memory block with the given
// configuration.
//
// This module includes flow control for reads, but unlike the
// standard library BRAM servers there is no flow control on puts. Put
// is always_ready, and read behaves like a Wire: the result of each
// put is available for a single cycle, and is lost if not read at
// that time.
module mkEBR#(EBRPortConfig cfgA,
              EBRPortConfig cfgB)
   (EBR#(addr_a, data_a, addr_b, data_b))
   provisos (Bits#(addr_a, addr_sz_a),
             Bits#(data_a, data_sz_a),
             Bits#(addr_b, addr_sz_b),
             Bits#(data_b, data_sz_b),
             Add#(addr_a_pad, addr_sz_a, 14),
             Add#(data_a_pad, data_sz_a, 18),
             Add#(addr_b_pad, addr_sz_b, 14),
             Add#(data_b_pad, data_sz_b, 18));

   let defaultClk <- exposeCurrentClock;
   let defaultRstN <- exposeCurrentReset;
   let rcfgA = resolvePortCfg("mkEBR", "A", addr_a ' (?), data_a ' (?), cfgA, defaultClk, defaultRstN);
   let rcfgB = resolvePortCfg("mkEBR", "B", addr_b ' (?), data_b ' (?), cfgB, defaultClk, defaultRstN);

   let mem <- mkEBRCore(cfgA, cfgB);

   DelayLine#(void) latencyA <- mkDelayLine(rcfgA.operation_latency, clocked_by(rcfgA.clk), reset_by(rcfgA.rstN));
   DelayLine#(void) latencyB <- mkDelayLine(rcfgB.operation_latency, clocked_by(rcfgB.clk), reset_by(rcfgB.rstN));

   interface EBRPort portA;
      method Action put(UInt#(3) chip_select, Bool write, addr_a address, data_a datain);
         mem.portA.put(chip_select, write, address, datain);
         if (rcfgA.write_outputs_data || !write)
            latencyA <= ?;
      endmethod
      method data_a read() if (rcfgA.enabled && latencyA.ready);
         return mem.portA.read();
      endmethod
   endinterface

   interface EBRPort portB;
      method Action put(UInt#(3) chip_select, Bool write, addr_b address, data_b datain);
         mem.portB.put(chip_select, write, address, datain);
         if (rcfgB.write_outputs_data || !write)
            latencyB <= ?;
      endmethod
      method data_b read() if (rcfgB.enabled && latencyB.ready);
         return mem.portB.read();
      endmethod
   endinterface
endmodule : mkEBR

////////////////////////////////////////////////////////////
// Utilities
//
// These are little helpers that I expected to find in the stdlib, but
// aren't there. Thankfully, they are easy to write by following the
// examples of similar helpers.

function WriteOnly#(a) discardingWriteOnly();
   return (interface WriteOnly
              method Action _write(a x);
                 noAction;
              endmethod
           endinterface);
endfunction

function WriteOnly#(a) regToWriteOnly(Reg#(a) r);
   return (interface WriteOnly
              method _write = r._write;
           endinterface);
endfunction

function ReadOnly#(a) constToReadOnly(a x);
   return (interface ReadOnly
              method _read;
                 return x;
              endmethod
           endinterface);
endfunction

endpackage