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kernel/mem: Add helpers for write port widening.

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This commit is contained in:
Marcelina Kościelnicka 2021-05-26 03:07:51 +02:00
parent 83a218141c
commit b019db1f37
2 changed files with 57 additions and 0 deletions
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46
kernel/mem.cc
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@ -798,3 +798,49 @@ void Mem::prepare_wr_merge(int idx1, int idx2) {
oport.priority_mask[idx1] = true;
}
}
void Mem::widen_prep(int wide_log2) {
// Make sure start_offset and size are aligned to the port width,
// adjust if necessary.
int mask = ((1 << wide_log2) - 1);
int delta = start_offset & mask;
start_offset -= delta;
size += delta;
if (size & mask) {
size |= mask;
size++;
}
}
void Mem::widen_wr_port(int idx, int wide_log2) {
widen_prep(wide_log2);
auto &port = wr_ports[idx];
log_assert(port.wide_log2 <= wide_log2);
if (port.wide_log2 < wide_log2) {
SigSpec new_data, new_en;
SigSpec addr_lo = port.addr.extract(0, wide_log2);
for (int sub = 0; sub < (1 << wide_log2); sub += (1 << port.wide_log2))
{
Const cur_addr_lo(sub, wide_log2);
if (addr_lo == cur_addr_lo) {
// Always writes to this subword.
new_data.append(port.data);
new_en.append(port.en);
} else if (addr_lo.is_fully_const()) {
// Never writes to this subword.
new_data.append(Const(State::Sx, GetSize(port.data)));
new_en.append(Const(State::S0, GetSize(port.data)));
} else {
// May or may not write to this subword.
new_data.append(port.data);
SigSpec addr_eq = module->Eq(NEW_ID, addr_lo, cur_addr_lo);
SigSpec en = module->Mux(NEW_ID, Const(State::S0, GetSize(port.data)), port.en, addr_eq);
new_en.append(en);
}
}
port.addr.replace(port.wide_log2, Const(State::S0, wide_log2 - port.wide_log2));
port.data = new_data;
port.en = new_en;
port.wide_log2 = wide_log2;
}
}

11
kernel/mem.h
View file

@ -109,6 +109,17 @@ struct Mem {
// is called.
void prepare_wr_merge(int idx1, int idx2);
// Prepares the memory for widening a port to a given width. This
// involves ensuring that start_offset and size are aligned to the
// target width.
void widen_prep(int wide_log2);
// Widens a write port up to a given width. The newly port is
// equivalent to the original, made by replicating enable/data bits
// and masking enable bits with decoders on the low part of the
// original address.
void widen_wr_port(int idx, int wide_log2);
Mem(Module *module, IdString memid, int width, int start_offset, int size) : module(module), memid(memid), packed(false), mem(nullptr), cell(nullptr), width(width), start_offset(start_offset), size(size) {}
};