Enhance the jump instruction (use RRO like call)

Author: semahawk

docs/spec.md

@@ -289,21 +289,27 @@ shiftr <reg>, <imm>
 
 Will effectively perform `reg = reg >> imm`. No side effects (at the moment).
 
-### jump (immediate address)
+### jump (using a register)
+
+Format: RRO
+
+Opcode: `7'h4`
 
 ```
-jump <imm>
+jump <reg> [, off <imm>]
 ```
 
-This instruction will set register `pc` to the specified `<imm>` value.
-
-### jump (using a register)
+This instruction will set register `pc` to the value taken of `<reg> + <imm>` (`<imm>` can be negative, so backward jumps are possible)
 
 ```
-jump <reg>
+jump <imm>
 ```
 
-This instruction will set register `pc` to the value taken from register `<reg>`.
+The assembler also supports this syntactic sugar syntax (so you can eg. jump to a label etc). When this is used the assembler will calculate the proper offset and implicitly use the `pc` register, turning it into this call:
+
+```
+jump pc, off <offset from current pc>
+```
 
 ### call (register, offset)
 
@@ -317,6 +323,12 @@ call <reg> off <imm>
 
 This instruction will effectively decrement the `sp` register by 8, issue a bus write cycle to write value of `pc + 8` into address `sp`, and make a jump to `reg + imm`.
 
+```
+call <imm>
+```
+
+The assembler also supports this syntactic sugar syntax. In this case, just like in the `jump` case, the assembler will implicitly use the `pc` register, and calculate the correct offset.
+
 ### return
 
 Format: I

rtl/cpu.v

@@ -401,16 +401,14 @@ module cpu (
                             end
                         end // `OP_LOAD
                         `OP_JUMP: begin
-                            if (instr_format == `INSTR_FORMAT_I) begin
-                                // $display("%g: jump 0h%01x", $time, instr_i_imm);
-
-                                cpu_regs_in <= instr_i_imm;
-                            end else if (instr_format == `INSTR_FORMAT_RIS) begin
-                                // $display("%g: jump r%1d (h'%x)", $time, instr_ris_reg, instr_dst_reg_val);
-
-                                cpu_regs_in <= instr_dst_reg_val;
-                            end
+                            if (instr_rro_off[40] == 1'b1)
+                                $display("%g: jump r%1d (h'%x) off -0x%1x", $time,
+                                    instr_rro_dst, instr_dst_reg_val, ~instr_rro_off + 1);
+                            else
+                                $display("%g: jump r%1d (h'%x) off 0x%1x", $time,
+                                    instr_rro_dst, instr_dst_reg_val, instr_rro_off);
 
+                            cpu_regs_in <= $signed(instr_dst_reg_val) + $signed(instr_rro_off);
                             cpu_regs_write <= 1'b1;
                             cpu_regs_id <= `REG_PC;
                             cpu_state <= `STATE_REG_WRITE;

rtl/rom.v

@@ -53,13 +53,16 @@ module rom (
 16'h0008: r_dat_o = 64'h1687800000008000; // add r30, 0x400 0
 16'h0010: r_dat_o = 64'h0286c01002000010; // set r27, 0x80100000 shl 16
 16'h0018: r_dat_o = 64'h02804000000002a0; // set r1, 0x15
-16'h0020: r_dat_o = 64'h1a07c00000000008; // call r31 off 8
-16'h0028: r_dat_o = 64'h0c87c00000000200; // sub r31, 16
-16'h0030: r_dat_o = 64'h0407360000000000; // load r28, r27
-16'h0038: r_dat_o = 64'h0a87000000000000; // testbit r28, 0
-16'h0040: r_dat_o = 64'h0948800000000030; // jump.nz 0x800000000030
-16'h0048: r_dat_o = 64'h0606c20000000010; // store r1, r27 off 16
-16'h0050: r_dat_o = 64'h1d00000000000000; // return
+16'h0020: r_dat_o = 64'h1a07c00000000020; // call r31 off 32
+16'h0028: r_dat_o = 64'h028680000004e200; // set r26, 0x2710
+16'h0030: r_dat_o = 64'h0c86800000000020; // sub r26, 1
+16'h0038: r_dat_o = 64'h084fc1fffffffff0; // jump.nz r31 off -16
+16'h0040: r_dat_o = 64'hff00000000000000; // halt
+16'h0048: r_dat_o = 64'h0407360000000000; // load r28, r27
+16'h0050: r_dat_o = 64'h0a87000000000000; // testbit r28, 0
+16'h0058: r_dat_o = 64'h084fc1ffffffffe8; // jump.nz r31 off -24
+16'h0060: r_dat_o = 64'h0606c20000000010; // store r1, r27 off 16
+16'h0068: r_dat_o = 64'h1d00000000000000; // return
             default:  r_dat_o = 64'hfe00000000000000; // halt by default
         endcase
     end

tools/asm.lark

@@ -1,7 +1,7 @@
 start: instr*
 instr: /nop/         ["." cond] -> nop
-     | /jump/        ["." cond] expr -> jump_i
-     | /jump/        ["." cond] reg -> jump_ris
+     | /jump/        ["." cond] expr -> jump_expr
+     | /jump/        ["." cond] reg ["off" expr] -> jump_rro
      | /call/        ["." cond] expr -> call_expr
      | /call/        ["." cond] reg ["off" expr] -> call_rro
      | /return/      ["." cond] -> return_

tools/asm.py

@@ -190,10 +190,8 @@ def __init__(self, mnem, opcode, format, cond, **kwargs):
         super().__init__(mnem, opcode, format, cond, **kwargs)
 
     def __str__(self):
-        if self.format == Format.I:
-            return "jump{} 0x{:x}".format(self.cond, self.imm)
-        elif self.format == Format.RIS:
-            return "jump{} r{}".format(self.cond, self.dst_reg)
+        if self.format == Format.RRO:
+            return "jump{} r{} {}".format(self.cond, self.dst_reg, self.off)
 
 class Call(Instr):
     def __init__(self, mnem, opcode, format, cond, **kwargs):
@@ -339,20 +337,27 @@ def halt(self, op, cond):
         self.inc_pc()
         return Halt("halt", 0x7f, Cond(cond))
 
-    def jump_i(self, op, cond, imm):
+    def jump_expr(self, op, cond, imm):
         self.inc_pc()
-        return Jump("jump", 0x04, Format.I, Cond(cond), imm = imm)
+        # this offset from pc must be calculated after it's been incremented
+        # since when the instruction is executed by the CPU, the pc register
+        # points to the next instruction, not current
+        offset_from_pc = imm - self.current_pc
+
+        return Jump("jump", 0x04, Format.RRO, Cond(cond),
+            dst_reg = 31, src_reg = 0x0, off = Off(offset_from_pc))
 
-    def jump_ris(self, op, cond, reg):
+    def jump_rro(self, op, cond, reg, off):
         self.inc_pc()
-        return Jump("jump", 0x04, Format.RIS, Cond(cond), dst_reg = reg)
+        return Jump("jump", 0x04, Format.RRO, Cond(cond),
+            dst_reg = reg, src_reg = 0x0, off = Off(off))
 
-    def call_expr(self, op, cond, special_imm):
+    def call_expr(self, op, cond, imm):
         self.inc_pc()
         # this offset from pc must be calculated after it's been incremented
         # since when the instruction is executed by the CPU, the pc register
         # points to the next instruction, not current
-        offset_from_pc = special_imm - self.current_pc
+        offset_from_pc = imm - self.current_pc
 
         return Call("call", 0x0d, Format.RRO, Cond(cond),
             dst_reg = 31, src_reg = 0x0, off = Off(offset_from_pc))