swap complicated bits, simplify ISACaller, reduce indent level
[openpower-isa.git] / src / openpower / decoder / isa / caller.py
index c325fe1eb39748e831884c25b061017ed5dea1c8..e51d24f62a731e006e0cab22f7ce1615c80964d4 100644 (file)
@@ -1142,7 +1142,7 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         in the class for later use.  this to avoid problems with yield
         """
         # go through all iterators in lock-step, advance to next remap_idx
-        srcstep, dststep, substep = self.get_src_dststeps()
+        srcstep, dststep, ssubstep, dsubstep = self.get_src_dststeps()
         # get four SVSHAPEs. here we are hard-coding
         SVSHAPE0 = self.spr['SVSHAPE0']
         SVSHAPE1 = self.spr['SVSHAPE1']
@@ -1236,6 +1236,7 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
                     'setvl', 'svindex', 'svremap', 'svstep', 'svshape',
                     'grev', 'ternlogi', 'bmask', 'cprop',
                     'absdu', 'absds', 'absdacs', 'absdacu', 'avgadd',
+                    'fmvis', 'fishmv',
                     ]:
             illegal = False
             ins_name = dotstrp
@@ -1294,11 +1295,11 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
                 self.update_nia()
                 self.update_pc_next()
                 return
-            srcstep, dststep, substep = self.get_src_dststeps()
+            srcstep, dststep, ssubstep, dsubstep = self.get_src_dststeps()
             pred_dst_zero = self.pred_dst_zero
             pred_src_zero = self.pred_src_zero
             vl = self.svstate.vl
-            subvl = self.svstate.subvl
+            subvl = yield self.dec2.rm_dec.rm_in.subvl
 
         # VL=0 in SVP64 mode means "do nothing: skip instruction"
         if self.is_svp64_mode and vl == 0:
@@ -1318,45 +1319,7 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         if persist or self.last_op_svshape:
             remaps = self.get_remap_indices()
         if self.is_svp64_mode and (persist or self.last_op_svshape):
-            # just some convenient debug info
-            for i in range(4):
-                sname = 'SVSHAPE%d' % i
-                shape = self.spr[sname]
-                log(sname, bin(shape.value))
-                log("    lims", shape.lims)
-                log("    mode", shape.mode)
-                log("    skip", shape.skip)
-
-            # set up the list of steps to remap
-            mi0 = self.svstate.mi0
-            mi1 = self.svstate.mi1
-            mi2 = self.svstate.mi2
-            mo0 = self.svstate.mo0
-            mo1 = self.svstate.mo1
-            steps = [(self.dec2.in1_step, mi0),  # RA
-                     (self.dec2.in2_step, mi1),  # RB
-                     (self.dec2.in3_step, mi2),  # RC
-                     (self.dec2.o_step, mo0),   # RT
-                     (self.dec2.o2_step, mo1),   # EA
-                     ]
-            remap_idxs = self.remap_idxs
-            rremaps = []
-            # now cross-index the required SHAPE for each of 3-in 2-out regs
-            rnames = ['RA', 'RB', 'RC', 'RT', 'EA']
-            for i, (dstep, shape_idx) in enumerate(steps):
-                (shape, remap) = remaps[shape_idx]
-                remap_idx = remap_idxs[shape_idx]
-                # zero is "disabled"
-                if shape.value == 0x0:
-                    continue
-                # now set the actual requested step to the current index
-                yield dstep.eq(remap_idx)
-
-                # debug printout info
-                rremaps.append((shape.mode, i, rnames[i], shape_idx,
-                                remap_idx))
-            for x in rremaps:
-                log("shape remap", x)
+            yield from self.remap_debug(remaps)
         # after that, settle down (combinatorial) to let Vector reg numbers
         # work themselves out
         yield Settle()
@@ -1369,30 +1332,11 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         # main input registers (RT, RA ...)
         inputs = []
         for name in input_names:
-            # using PowerDecoder2, first, find the decoder index.
-            # (mapping name RA RB RC RS to in1, in2, in3)
-            regnum, is_vec = yield from get_pdecode_idx_in(self.dec2, name)
-            if regnum is None:
-                # doing this is not part of svp64, it's because output
-                # registers, to be modified, need to be in the namespace.
-                regnum, is_vec = yield from get_pdecode_idx_out(self.dec2, name)
-            if regnum is None:
-                regnum, is_vec = yield from get_pdecode_idx_out2(self.dec2,
-                                                                 name)
-
-            # in case getting the register number is needed, _RA, _RB
-            regname = "_" + name
-            self.namespace[regname] = regnum
-            if not self.is_svp64_mode or not pred_src_zero:
-                log('reading reg %s %s' % (name, str(regnum)), is_vec)
-                if name in fregs:
-                    reg_val = SelectableInt(self.fpr(regnum))
-                elif name is not None:
-                    reg_val = SelectableInt(self.gpr(regnum))
-            else:
-                log('zero input reg %s %s' % (name, str(regnum)), is_vec)
-                reg_val = 0
-            inputs.append(reg_val)
+            print("name", name)
+            regval = (yield from self.get_input(name))
+            print("regval", regval)
+            inputs.append(regval)
+
         # arrrrgh, awful hack, to get _RT into namespace
         if ins_name in ['setvl', 'svstep']:
             regname = "_RT"
@@ -1406,71 +1350,8 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         # in SVP64 mode for LD/ST work out immediate
         # XXX TODO: replace_ds for DS-Form rather than D-Form.
         # use info.form to detect
-        replace_d = False  # update / replace constant in pseudocode
         if self.is_svp64_mode:
-            ldstmode = yield self.dec2.rm_dec.ldstmode
-            # shift mode reads SVD (or SVDS - TODO)
-            # *BUT*... because this is "overloading" of LD operations,
-            # it gets *STORED* into D (or DS, TODO)
-            if ldstmode == SVP64LDSTmode.SHIFT.value:
-                imm = yield self.dec2.dec.fields.FormSVD.SVD[0:11]
-                imm = exts(imm, 11)  # sign-extend to integer
-                log("shift SVD", imm)
-                replace_d = True
-            else:
-                if info.form == 'DS':
-                    # DS-Form, multiply by 4 then knock 2 bits off after
-                    imm = yield self.dec2.dec.fields.FormDS.DS[0:14] * 4
-                else:
-                    imm = yield self.dec2.dec.fields.FormD.D[0:16]
-                imm = exts(imm, 16)  # sign-extend to integer
-            # get the right step. LD is from srcstep, ST is dststep
-            op = yield self.dec2.e.do.insn_type
-            offsmul = 0
-            if op == MicrOp.OP_LOAD.value:
-                if remap_active:
-                    offsmul = yield self.dec2.in1_step
-                    log("D-field REMAP src", imm, offsmul)
-                else:
-                    offsmul = (srcstep * (subvl+1)) + substep
-                    log("D-field src", imm, offsmul)
-            elif op == MicrOp.OP_STORE.value:
-                # XXX NOTE! no bit-reversed STORE! this should not ever be used
-                offsmul = (dststep * (subvl+1)) + substep
-                log("D-field dst", imm, offsmul)
-            # bit-reverse mode, rev already done through get_src_dst_steps()
-            if ldstmode == SVP64LDSTmode.SHIFT.value:
-                # manually look up RC, sigh
-                RC = yield self.dec2.dec.RC[0:5]
-                RC = self.gpr(RC)
-                log("LD-SHIFT:", "VL", vl,
-                    "RC", RC.value, "imm", imm,
-                    "offs", bin(offsmul),
-                    )
-                imm = SelectableInt((imm * offsmul) << RC.value, 32)
-            # Unit-Strided LD/ST adds offset*width to immediate
-            elif ldstmode == SVP64LDSTmode.UNITSTRIDE.value:
-                ldst_len = yield self.dec2.e.do.data_len
-                imm = SelectableInt(imm + offsmul * ldst_len, 32)
-                replace_d = True
-            # Element-strided multiplies the immediate by element step
-            elif ldstmode == SVP64LDSTmode.ELSTRIDE.value:
-                imm = SelectableInt(imm * offsmul, 32)
-                replace_d = True
-            if replace_d:
-                ldst_ra_vec = yield self.dec2.rm_dec.ldst_ra_vec
-                ldst_imz_in = yield self.dec2.rm_dec.ldst_imz_in
-                log("LDSTmode", SVP64LDSTmode(ldstmode),
-                    offsmul, imm, ldst_ra_vec, ldst_imz_in)
-        # new replacement D... errr.. DS
-        if replace_d:
-            if info.form == 'DS':
-                # TODO: assert 2 LSBs are zero?
-                log("DS-Form, TODO, assert 2 LSBs zero?", bin(imm.value))
-                imm.value = imm.value >> 2
-                self.namespace['DS'] = imm
-            else:
-                self.namespace['D'] = imm
+            yield from self.check_replace_d(info, remap_active)
 
         # "special" registers
         for special in info.special_regs:
@@ -1561,52 +1442,176 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         # any modified return results?
         if info.write_regs:
             for name, output in zip(output_names, results):
-                if name == 'overflow':  # ignore, done already (above)
-                    continue
-                if isinstance(output, int):
-                    output = SelectableInt(output, 256)
-                if name in ['CA', 'CA32']:
-                    if carry_en:
-                        log("writing %s to XER" % name, output)
-                        self.spr['XER'][XER_bits[name]] = output.value
-                    else:
-                        log("NOT writing %s to XER" % name, output)
-                elif name in info.special_regs:
-                    log('writing special %s' % name, output, special_sprs)
-                    if name in special_sprs:
-                        self.spr[name] = output
-                    else:
-                        self.namespace[name].eq(output)
-                    if name == 'MSR':
-                        log('msr written', hex(self.msr.value))
+                yield from self.check_write(info, name, output, carry_en)
+
+        nia_update = (yield from self.check_step_increment(results, rc_en,
+                                                           asmop, ins_name))
+        if nia_update:
+            self.update_pc_next()
+
+    def check_replace_d(self, info, remap_active):
+        replace_d = False  # update / replace constant in pseudocode
+        ldstmode = yield self.dec2.rm_dec.ldstmode
+        vl = self.svstate.vl
+        subvl = yield self.dec2.rm_dec.rm_in.subvl
+        srcstep, dststep = self.new_srcstep, self.new_dststep
+        ssubstep, dsubstep = self.new_ssubstep, self.new_dsubstep
+        if info.form == 'DS':
+            # DS-Form, multiply by 4 then knock 2 bits off after
+            imm = yield self.dec2.dec.fields.FormDS.DS[0:14] * 4
+        else:
+            imm = yield self.dec2.dec.fields.FormD.D[0:16]
+        imm = exts(imm, 16)  # sign-extend to integer
+        # get the right step. LD is from srcstep, ST is dststep
+        op = yield self.dec2.e.do.insn_type
+        offsmul = 0
+        if op == MicrOp.OP_LOAD.value:
+            if remap_active:
+                offsmul = yield self.dec2.in1_step
+                log("D-field REMAP src", imm, offsmul)
+            else:
+                offsmul = (srcstep * (subvl+1)) + ssubstep
+                log("D-field src", imm, offsmul)
+        elif op == MicrOp.OP_STORE.value:
+            # XXX NOTE! no bit-reversed STORE! this should not ever be used
+            offsmul = (dststep * (subvl+1)) + dsubstep
+            log("D-field dst", imm, offsmul)
+        # Unit-Strided LD/ST adds offset*width to immediate
+        if ldstmode == SVP64LDSTmode.UNITSTRIDE.value:
+            ldst_len = yield self.dec2.e.do.data_len
+            imm = SelectableInt(imm + offsmul * ldst_len, 32)
+            replace_d = True
+        # Element-strided multiplies the immediate by element step
+        elif ldstmode == SVP64LDSTmode.ELSTRIDE.value:
+            imm = SelectableInt(imm * offsmul, 32)
+            replace_d = True
+        if replace_d:
+            ldst_ra_vec = yield self.dec2.rm_dec.ldst_ra_vec
+            ldst_imz_in = yield self.dec2.rm_dec.ldst_imz_in
+            log("LDSTmode", SVP64LDSTmode(ldstmode),
+                offsmul, imm, ldst_ra_vec, ldst_imz_in)
+        # new replacement D... errr.. DS
+        if replace_d:
+            if info.form == 'DS':
+                # TODO: assert 2 LSBs are zero?
+                log("DS-Form, TODO, assert 2 LSBs zero?", bin(imm.value))
+                imm.value = imm.value >> 2
+                self.namespace['DS'] = imm
+            else:
+                self.namespace['D'] = imm
+
+    def get_input(self, name):
+        # using PowerDecoder2, first, find the decoder index.
+        # (mapping name RA RB RC RS to in1, in2, in3)
+        regnum, is_vec = yield from get_pdecode_idx_in(self.dec2, name)
+        if regnum is None:
+            # doing this is not part of svp64, it's because output
+            # registers, to be modified, need to be in the namespace.
+            regnum, is_vec = yield from get_pdecode_idx_out(self.dec2, name)
+        if regnum is None:
+            regnum, is_vec = yield from get_pdecode_idx_out2(self.dec2, name)
+
+        # in case getting the register number is needed, _RA, _RB
+        regname = "_" + name
+        self.namespace[regname] = regnum
+        if not self.is_svp64_mode or not self.pred_src_zero:
+            log('reading reg %s %s' % (name, str(regnum)), is_vec)
+            if name in fregs:
+                reg_val = SelectableInt(self.fpr(regnum))
+            elif name is not None:
+                reg_val = SelectableInt(self.gpr(regnum))
+        else:
+            log('zero input reg %s %s' % (name, str(regnum)), is_vec)
+            reg_val = 0
+        return reg_val
+
+    def remap_debug(self, remaps):
+        # just some convenient debug info
+        for i in range(4):
+            sname = 'SVSHAPE%d' % i
+            shape = self.spr[sname]
+            log(sname, bin(shape.value))
+            log("    lims", shape.lims)
+            log("    mode", shape.mode)
+            log("    skip", shape.skip)
+
+        # set up the list of steps to remap
+        mi0 = self.svstate.mi0
+        mi1 = self.svstate.mi1
+        mi2 = self.svstate.mi2
+        mo0 = self.svstate.mo0
+        mo1 = self.svstate.mo1
+        steps = [(self.dec2.in1_step, mi0),  # RA
+                 (self.dec2.in2_step, mi1),  # RB
+                 (self.dec2.in3_step, mi2),  # RC
+                 (self.dec2.o_step, mo0),   # RT
+                 (self.dec2.o2_step, mo1),   # EA
+                 ]
+        remap_idxs = self.remap_idxs
+        rremaps = []
+        # now cross-index the required SHAPE for each of 3-in 2-out regs
+        rnames = ['RA', 'RB', 'RC', 'RT', 'EA']
+        for i, (dstep, shape_idx) in enumerate(steps):
+            (shape, remap) = remaps[shape_idx]
+            remap_idx = remap_idxs[shape_idx]
+            # zero is "disabled"
+            if shape.value == 0x0:
+                continue
+            # now set the actual requested step to the current index
+            yield dstep.eq(remap_idx)
+
+            # debug printout info
+            rremaps.append((shape.mode, i, rnames[i], shape_idx, remap_idx))
+        for x in rremaps:
+            log("shape remap", x)
+
+    def check_write(self, info, name, output, carry_en):
+        if name == 'overflow':  # ignore, done already (above)
+            return
+        if isinstance(output, int):
+            output = SelectableInt(output, 256)
+        if name in ['CA', 'CA32']:
+            if carry_en:
+                log("writing %s to XER" % name, output)
+                self.spr['XER'][XER_bits[name]] = output.value
+            else:
+                log("NOT writing %s to XER" % name, output)
+        elif name in info.special_regs:
+            log('writing special %s' % name, output, special_sprs)
+            if name in special_sprs:
+                self.spr[name] = output
+            else:
+                self.namespace[name].eq(output)
+            if name == 'MSR':
+                log('msr written', hex(self.msr.value))
+        else:
+            regnum, is_vec = yield from get_pdecode_idx_out(self.dec2, name)
+            if regnum is None:
+                regnum, is_vec = yield from get_pdecode_idx_out2(
+                    self.dec2, name)
+            if regnum is None:
+                # temporary hack for not having 2nd output
+                regnum = yield getattr(self.decoder, name)
+                is_vec = False
+            if self.is_svp64_mode and self.pred_dst_zero:
+                log('zeroing reg %d %s' % (regnum, str(output)),
+                    is_vec)
+                output = SelectableInt(0, 256)
+            else:
+                if name in fregs:
+                    ftype = 'fpr'
                 else:
-                    regnum, is_vec = yield from get_pdecode_idx_out(self.dec2,
-                                                                    name)
-                    if regnum is None:
-                        regnum, is_vec = yield from get_pdecode_idx_out2(
-                            self.dec2, name)
-                    if regnum is None:
-                        # temporary hack for not having 2nd output
-                        regnum = yield getattr(self.decoder, name)
-                        is_vec = False
-                    if self.is_svp64_mode and pred_dst_zero:
-                        log('zeroing reg %d %s' % (regnum, str(output)),
-                            is_vec)
-                        output = SelectableInt(0, 256)
-                    else:
-                        if name in fregs:
-                            ftype = 'fpr'
-                        else:
-                            ftype = 'gpr'
-                        log('writing %s %s %s' % (ftype, regnum, str(output)),
-                            is_vec)
-                    if output.bits > 64:
-                        output = SelectableInt(output.value, 64)
-                    if name in fregs:
-                        self.fpr[regnum] = output
-                    else:
-                        self.gpr[regnum] = output
+                    ftype = 'gpr'
+                log('writing %s %s %s' % (ftype, regnum, str(output)),
+                    is_vec)
+            if output.bits > 64:
+                output = SelectableInt(output.value, 64)
+            if name in fregs:
+                self.fpr[regnum] = output
+            else:
+                self.gpr[regnum] = output
 
+    def check_step_increment(self, results, rc_en, asmop, ins_name):
         # check if it is the SVSTATE.src/dest step that needs incrementing
         # this is our Sub-Program-Counter loop from 0 to VL-1
         pre = False
@@ -1623,62 +1628,62 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
                 self.svp64_reset_loop()
                 self.svstate.vfirst = 0
                 self.update_nia()
-                if rc_en:
-                    results = [SelectableInt(0, 64)]
-                    self.handle_comparison(results)  # CR0
+                if not rc_en:
+                    return True
+                results = [SelectableInt(0, 64)]
+                self.handle_comparison(results)  # CR0
+                return True
+            if self.allow_next_step_inc == 2:
+                log("SVSTATE_NEXT: read")
+                nia_update = (yield from self.svstate_post_inc(ins_name))
             else:
-                if self.allow_next_step_inc == 2:
-                    log("SVSTATE_NEXT: read")
-                    nia_update = (yield from self.svstate_post_inc(ins_name))
-                else:
-                    log("SVSTATE_NEXT: post-inc")
-                # use actual src/dst-step here to check end, do NOT
-                # use bit-reversed version
-                srcstep, dststep, substep = \
-                    self.new_srcstep, self.new_dststep, self.new_substep
-                remaps = self.get_remap_indices()
-                remap_idxs = self.remap_idxs
-                vl = self.svstate.vl
-                subvl = self.svstate.subvl
-                end_sub = substep == subvl
-                end_src = srcstep == vl-1
-                end_dst = dststep == vl-1
-                if self.allow_next_step_inc != 2:
-                    self.advance_svstate_steps(end_src, end_dst)
-                self.namespace['SVSTATE'] = self.svstate.spr
-                # set CR0 (if Rc=1) based on end
-                if rc_en:
-                    endtest = 1 if (end_src or end_dst) else 0
-                    #results = [SelectableInt(endtest, 64)]
-                    # self.handle_comparison(results) # CR0
-
-                    # see if svstep was requested, if so, which SVSTATE
-                    endings = 0b111
-                    if self.svstate_next_mode > 0:
-                        shape_idx = self.svstate_next_mode.value-1
-                        endings = self.remap_loopends[shape_idx]
-                    cr_field = SelectableInt((~endings) << 1 | endtest, 4)
-                    print("svstep Rc=1, CR0", cr_field)
-                    self.crl[0].eq(cr_field)  # CR0
-                if end_src or end_dst:
-                    # reset at end of loop including exit Vertical Mode
-                    log("SVSTATE_NEXT: after increments, reset")
-                    self.svp64_reset_loop()
-                    self.svstate.vfirst = 0
-
-        elif self.is_svp64_mode:
-            nia_update = (yield from self.svstate_post_inc(ins_name))
-        else:
-            # XXX only in non-SVP64 mode!
-            # record state of whether the current operation was an svshape,
-            # OR svindex!
-            # to be able to know if it should apply in the next instruction.
-            # also (if going to use this instruction) should disable ability
-            # to interrupt in between. sigh.
-            self.last_op_svshape = asmop in ['svremap', 'svindex']
+                log("SVSTATE_NEXT: post-inc")
+            # use actual src/dst-step here to check end, do NOT
+            # use bit-reversed version
+            srcstep, dststep = self.new_srcstep, self.new_dststep
+            ssubstep, dsubstep = self.new_ssubstep, self.new_dsubstep
+            remaps = self.get_remap_indices()
+            remap_idxs = self.remap_idxs
+            vl = self.svstate.vl
+            subvl = yield self.dec2.rm_dec.rm_in.subvl
+            end_src = srcstep == vl-1
+            end_dst = dststep == vl-1
+            if self.allow_next_step_inc != 2:
+                yield from self.advance_svstate_steps(end_src, end_dst)
+            self.namespace['SVSTATE'] = self.svstate.spr
+            # set CR0 (if Rc=1) based on end
+            if rc_en:
+                endtest = 1 if (end_src or end_dst) else 0
+                #results = [SelectableInt(endtest, 64)]
+                # self.handle_comparison(results) # CR0
+
+                # see if svstep was requested, if so, which SVSTATE
+                endings = 0b111
+                if self.svstate_next_mode > 0:
+                    shape_idx = self.svstate_next_mode.value-1
+                    endings = self.remap_loopends[shape_idx]
+                cr_field = SelectableInt((~endings) << 1 | endtest, 4)
+                print("svstep Rc=1, CR0", cr_field)
+                self.crl[0].eq(cr_field)  # CR0
+            if end_src or end_dst:
+                # reset at end of loop including exit Vertical Mode
+                log("SVSTATE_NEXT: after increments, reset")
+                self.svp64_reset_loop()
+                self.svstate.vfirst = 0
+            return nia_update
 
-        if nia_update:
-            self.update_pc_next()
+        if self.is_svp64_mode:
+            return (yield from self.svstate_post_inc(ins_name))
+
+        # XXX only in non-SVP64 mode!
+        # record state of whether the current operation was an svshape,
+        # OR svindex!
+        # to be able to know if it should apply in the next instruction.
+        # also (if going to use this instruction) should disable ability
+        # to interrupt in between. sigh.
+        self.last_op_svshape = asmop in ['svremap', 'svindex']
+
+        return True
 
     def SVSTATE_NEXT(self, mode, submode):
         """explicitly moves srcstep/dststep on to next element, for
@@ -1705,25 +1710,31 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
 
     def svstate_pre_inc(self):
         """check if srcstep/dststep need to skip over masked-out predicate bits
+        note that this is not supposed to do anything to substep,
+        it is purely for skipping masked-out bits
         """
         # get SVSTATE VL (oh and print out some debug stuff)
         vl = self.svstate.vl
-        subvl = self.svstate.subvl
+        subvl = yield self.dec2.rm_dec.rm_in.subvl
         srcstep = self.svstate.srcstep
         dststep = self.svstate.dststep
-        substep = self.svstate.substep
+        ssubstep = self.svstate.ssubstep
+        dsubstep = self.svstate.dsubstep
         sv_a_nz = yield self.dec2.sv_a_nz
         fft_mode = yield self.dec2.use_svp64_fft
         in1 = yield self.dec2.e.read_reg1.data
-        log("SVP64: VL, subvl, srcstep, dststep, substep, sv_a_nz, "
+        log("SVP64: VL, subvl, srcstep, dststep, ssubstep, dsybstep, sv_a_nz, "
             "in1 fft, svp64",
-            vl, subvl, srcstep, dststep, substep, sv_a_nz, in1, fft_mode,
+            vl, subvl, srcstep, dststep, ssubstep, dsubstep,
+            sv_a_nz, in1, fft_mode,
             self.is_svp64_mode)
 
         # get predicate mask (all 64 bits)
         srcmask = dstmask = 0xffff_ffff_ffff_ffff
 
         pmode = yield self.dec2.rm_dec.predmode
+        pack = yield self.dec2.rm_dec.pack
+        unpack = yield self.dec2.rm_dec.unpack
         reverse_gear = yield self.dec2.rm_dec.reverse_gear
         sv_ptype = yield self.dec2.dec.op.SV_Ptype
         srcpred = yield self.dec2.rm_dec.srcpred
@@ -1738,9 +1749,11 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
             srcmask = dstmask = get_predcr(self.crl, dstpred, vl)
             if sv_ptype == SVPtype.P2.value:
                 srcmask = get_predcr(self.crl, srcpred, vl)
-        # work out if the substeps are completed
-        end_sub = substep == subvl
+        # work out if the ssubsteps are completed
+        ssubstart = ssubstep == 0
+        dsubstart = dsubstep == 0
         log("    pmode", pmode)
+        log("    pack/unpack", pack, unpack)
         log("    reverse", reverse_gear)
         log("    ptype", sv_ptype)
         log("    srcpred", bin(srcpred))
@@ -1749,25 +1762,25 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         log("    dstmask", bin(dstmask))
         log("    pred_sz", bin(pred_src_zero))
         log("    pred_dz", bin(pred_dst_zero))
-        log("    end_sub", end_sub)
+        log("    ssubstart", ssubstart)
+        log("    dsubstart", dsubstart)
 
-        if end_sub:
-            # okaaay, so here we simply advance srcstep (TODO dststep)
+        # okaaay, so here we simply advance srcstep (TODO dststep)
+        # this can ONLY be done at the beginning of the "for" loop
+        # (this is all actually a FSM so it's hell to keep track sigh)
+        if ssubstart:
             # until the predicate mask has a "1" bit... or we run out of VL
             # let srcstep==VL be the indicator to move to next instruction
             if not pred_src_zero:
                 while (((1 << srcstep) & srcmask) == 0) and (srcstep != vl):
-                    log("      skip", bin(1 << srcstep))
+                    log("      sskip", bin(1 << srcstep))
                     srcstep += 1
+        if dsubstart:
             # same for dststep
             if not pred_dst_zero:
                 while (((1 << dststep) & dstmask) == 0) and (dststep != vl):
-                    log("      skip", bin(1 << dststep))
+                    log("      dskip", bin(1 << dststep))
                     dststep += 1
-            # and reset substep back to zero
-            substep = 0
-        else:
-            substep += 1 # advance substep
 
         # now work out if the relevant mask bits require zeroing
         if pred_dst_zero:
@@ -1776,38 +1789,43 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
             pred_src_zero = ((1 << srcstep) & srcmask) == 0
 
         # store new srcstep / dststep
-        self.new_srcstep, self.new_dststep, self.new_substep = \
-                (srcstep, dststep, substep)
-        self.pred_dst_zero, self.pred_src_zero = pred_dst_zero, pred_src_zero
+        self.new_srcstep, self.new_dststep = (srcstep, dststep)
+        self.new_ssubstep, self.new_dsubstep = (ssubstep, dsubstep)
+        self.pred_dst_zero, self.pred_src_zero = (pred_dst_zero, pred_src_zero)
         log("    new srcstep", srcstep)
         log("    new dststep", dststep)
-        log("    new substep", substep)
+        log("    new ssubstep", ssubstep)
+        log("    new dsubstep", dsubstep)
 
     def get_src_dststeps(self):
-        """gets srcstep, dststep, and substep
+        """gets srcstep, dststep, and ssubstep, dsubstep
         """
-        return self.new_srcstep, self.new_dststep, self.new_substep
+        return (self.new_srcstep, self.new_dststep,
+                self.new_ssubstep, self.new_dsubstep)
 
     def update_new_svstate_steps(self):
         # note, do not get the bit-reversed srcstep here!
-        srcstep, dststep, substep = \
-            self.new_srcstep, self.new_dststep, self.new_substep
+        srcstep, dststep = self.new_srcstep, self.new_dststep
+        ssubstep, dsubstep = self.new_ssubstep, self.new_dsubstep
 
         # update SVSTATE with new srcstep
         self.svstate.srcstep = srcstep
         self.svstate.dststep = dststep
-        self.svstate.substep = substep
+        self.svstate.ssubstep = ssubstep
+        self.svstate.dsubstep = dsubstep
         self.namespace['SVSTATE'] = self.svstate
         yield self.dec2.state.svstate.eq(self.svstate.value)
         yield Settle()  # let decoder update
         srcstep = self.svstate.srcstep
         dststep = self.svstate.dststep
-        substep = self.svstate.substep
+        ssubstep = self.svstate.ssubstep
+        dsubstep = self.svstate.dsubstep
         vl = self.svstate.vl
-        subvl = self.svstate.subvl
+        subvl = yield self.dec2.rm_dec.rm_in.subvl
         log("    srcstep", srcstep)
         log("    dststep", dststep)
-        log("    substep", substep)
+        log("    ssubstep", ssubstep)
+        log("    dsubstep", dsubstep)
         log("         vl", vl)
         log("      subvl", subvl)
 
@@ -1827,11 +1845,12 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         # this is our Sub-Program-Counter loop from 0 to VL-1
         # XXX twin predication TODO
         vl = self.svstate.vl
-        subvl = self.svstate.subvl
+        subvl = yield self.dec2.rm_dec.rm_in.subvl
         mvl = self.svstate.maxvl
         srcstep = self.svstate.srcstep
         dststep = self.svstate.dststep
-        substep = self.svstate.substep
+        ssubstep = self.svstate.ssubstep
+        dsubstep = self.svstate.dsubstep
         rm_mode = yield self.dec2.rm_dec.mode
         reverse_gear = yield self.dec2.rm_dec.reverse_gear
         sv_ptype = yield self.dec2.dec.op.SV_Ptype
@@ -1839,10 +1858,11 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
         in_vec = not (yield self.dec2.no_in_vec)
         log("    svstate.vl", vl)
         log("    svstate.mvl", mvl)
-        log("    svstate.subvl", subvl)
+        log("         rm.subvl", subvl)
         log("    svstate.srcstep", srcstep)
         log("    svstate.dststep", dststep)
-        log("    svstate.substep", substep)
+        log("    svstate.ssubstep", ssubstep)
+        log("    svstate.dsubstep", dsubstep)
         log("    mode", rm_mode)
         log("    reverse", reverse_gear)
         log("    out_vec", out_vec)
@@ -1864,36 +1884,50 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
                 self.svp64_reset_loop()
                 self.update_pc_next()
                 return False
-        if svp64_is_vector and srcstep != vl-1 and dststep != vl-1:
-            self.advance_svstate_steps()
-            self.namespace['SVSTATE'] = self.svstate
-            # not an SVP64 branch, so fix PC (NIA==CIA) for next loop
-            # (by default, NIA is CIA+4 if v3.0B or CIA+8 if SVP64)
-            # this way we keep repeating the same instruction (with new steps)
-            self.pc.NIA.value = self.pc.CIA.value
-            self.namespace['NIA'] = self.pc.NIA
-            log("end of sub-pc call", self.namespace['CIA'],
-                self.namespace['NIA'])
-            return False  # DO NOT allow PC update whilst Sub-PC loop running
+        # loops end at the first "hit" (source or dest)
+        loopend = ((srcstep == vl-1 and ssubstep == subvl) or
+                   (dststep == vl-1 and dsubstep == subvl))
+        if not svp64_is_vector or loopend:
+            # reset loop to zero and update NIA
+            self.svp64_reset_loop()
+            self.update_nia()
 
-        # reset loop to zero and update NIA
-        self.svp64_reset_loop()
-        self.update_nia()
+            return True
 
-        return True
+        # still looping, advance and update NIA
+        yield from self.advance_svstate_steps()
+        self.namespace['SVSTATE'] = self.svstate
+        # not an SVP64 branch, so fix PC (NIA==CIA) for next loop
+        # (by default, NIA is CIA+4 if v3.0B or CIA+8 if SVP64)
+        # this way we keep repeating the same instruction (with new steps)
+        self.pc.NIA.value = self.pc.CIA.value
+        self.namespace['NIA'] = self.pc.NIA
+        log("end of sub-pc call", self.namespace['CIA'], self.namespace['NIA'])
+        return False  # DO NOT allow PC update whilst Sub-PC loop running
 
     def advance_svstate_steps(self, end_src=False, end_dst=False):
-        subvl = self.svstate.subvl
-        substep = self.svstate.substep
-        end_sub = substep == subvl
+        """ advance sub/steps. note that Pack/Unpack *INVERTS* the order.
+        TODO when Pack/Unpack is set, substep becomes the *outer* loop
+        """
+        subvl = yield self.dec2.rm_dec.rm_in.subvl
+        # first source step
+        ssubstep = self.svstate.ssubstep
+        end_sub = ssubstep == subvl
         if end_sub:
             if not end_src:
                 self.svstate.srcstep += SelectableInt(1, 7)
+            self.svstate.ssubstep = SelectableInt(0, 2)  # reset
+        else:
+            self.svstate.ssubstep += SelectableInt(1, 2) # advance ssubstep
+        # now dest step
+        dsubstep = self.svstate.dsubstep
+        end_sub = dsubstep == subvl
+        if end_sub:
             if not end_dst:
                 self.svstate.dststep += SelectableInt(1, 7)
-            self.svstate.substep = SelectableInt(0, 2)
+            self.svstate.dsubstep = SelectableInt(0, 2)  # reset
         else:
-            self.svstate.substep += SelectableInt(1, 2) # advance substep
+            self.svstate.dsubstep += SelectableInt(1, 2) # advance ssubstep
 
     def update_pc_next(self):
         # UPDATE program counter
@@ -1906,7 +1940,8 @@ class ISACaller(ISACallerHelper, ISAFPHelpers):
     def svp64_reset_loop(self):
         self.svstate.srcstep = 0
         self.svstate.dststep = 0
-        self.svstate.substep = 0
+        self.svstate.ssubstep = 0
+        self.svstate.dsubstep = 0
         log("    svstate.srcstep loop end (PC to update)")
         self.namespace['SVSTATE'] = self.svstate