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vram: document MemArbiter, fix round-robin ordering bug

This commit is contained in:
David Anderson 2024-09-08 13:31:53 -07:00
parent f31f64f5a2
commit 191cd1bfa2
2 changed files with 92 additions and 44 deletions
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58
vram/MemArbiter.bsv
View File

@ -8,25 +8,26 @@ export MemArbiterServer(..);
export MemArbiterClient(..);
export MemArbiter(..), mkPriorityMemArbiter, mkRoundRobinMemArbiter;
// A MemArbiterOp is an operation that a client is seeking permission
// to perform.
typedef struct {
Bool write;
addr addr;
} MemArbiterOp#(type addr) deriving (Bits, Eq, FShow);
// A MemArbiterServer receives requests for memory access and emits
// grants.
// A MemArbiterServer receives requests and emits grants.
interface MemArbiterServer#(type addr);
method Action request(MemArbiterOp#(addr) req);
method Bool grant();
endinterface
// A MemArbiterClient emits requests for memory access and emits
// grants.
// A MemArbiterClient emits requests and receives grants.
interface MemArbiterClient#(type addr);
method Maybe#(MemArbiterOp#(addr)) request();
method Action grant();
endinterface
// Arbiter clients and servers can be connected in the obvious way.
instance Connectable#(MemArbiterClient#(addr), MemArbiterServer#(addr));
module mkConnection(MemArbiterClient#(addr) client, MemArbiterServer#(addr) server, Empty ifc);
rule send_request (client.request matches tagged Valid .req);
@ -39,12 +40,42 @@ instance Connectable#(MemArbiterClient#(addr), MemArbiterServer#(addr));
endmodule
endinstance
// A MemArbiter manages concurrent access to a memory port.
interface MemArbiter#(numeric type num_clients, type addr);
// ports allow clients to request memory access.
interface Vector#(num_clients, MemArbiterServer#(addr)) ports;
// The following methods are to support arbiter chaining.
//
// Suppose you're arbitrating access to a dual-port
// memory. Typically, such a memory specifies that if one port is
// writing to an address, the other must not concurrently read or
// write that same address. This means the arbiters attached to
// each memory port must cooperate to avoid simultaneously granting
// conflicting requests from their clients.
//
// Calling forbid_addr prevents the arbiter from granting a
// concurrent request to access the given address. forbidden_addr
// emits the address for which a write access is being granted.
//
// MemArbiter intances are Connectable: mkConnection(a, b) gives
// conflict priority to a. That is, b will not grant requests that
// conflict with the grant that a has emitted.
method Action forbid_addr(addr addr);
method addr forbidden_addr();
endinterface
instance Connectable#(MemArbiter#(m, addr), MemArbiter#(n, addr));
module mkConnection(MemArbiter#(m, addr) a, MemArbiter#(n, addr) b, Empty ifc);
(* fire_when_enabled *)
rule forward_forbid;
b.forbid_addr(a.forbidden_addr);
endrule
endmodule
endinstance
// mkPriorityMemArbiter returns a MemArbiter that gives priority to
// lower numbered ports.
module mkPriorityMemArbiter(MemArbiter#(num_clients, addr))
provisos (Bits#(addr, _),
Eq#(addr),
@ -98,8 +129,9 @@ typedef struct {
Maybe#(addr) blocked_addr;
} GrantResult#(numeric type n, type addr) deriving (Bits, Eq, FShow);
// select_grant computes which one entry of requests should be granted.
function GrantResult#(n, addr) select_grant(Vector#(n, Maybe#(MemArbiterOp#(addr))) requests,
UInt#(TLog#(n)) lopri,
UInt#(TLog#(n)) hipri,
Maybe#(addr) block_addr)
provisos (Eq#(addr));
@ -130,7 +162,7 @@ function GrantResult#(n, addr) select_grant(Vector#(n, Maybe#(MemArbiterOp#(addr
endfunction
let in = zip(map(fromInteger, genVector()), requests);
let rot = reverse(rotateBy(reverse(in), lopri));
let rot = rotateBy(in, fromInteger(valueOf(n)-1)-hipri+1);
let seed = GrantResult{
granted: False,
grant_vec: replicate(False),
@ -151,10 +183,11 @@ module mkRoundRobinMemArbiter(MemArbiter#(num_clients, addr))
RWire#(addr) blocked_in <- mkRWire();
Wire#(Maybe#(addr)) blocked_out <- mkBypassWire();
// low_priority is the index of the client that should be last in
// high_prio is the index of the client that should be first in
// line to receive access. Every time we grant access to a client,
// that client becomes low_priority for the next round.
Reg#(UInt#(TLog#(num_clients))) low_priority <- mkReg(0);
// the one after that in sequence becomes high_prio in the next
// round.
Reg#(UInt#(TLog#(num_clients))) high_prio <- mkReg(0);
function Maybe#(_t) get_mreq(RWire#(_t) w);
return w.wget();
@ -162,11 +195,14 @@ module mkRoundRobinMemArbiter(MemArbiter#(num_clients, addr))
rule grant;
let in = map(get_mreq, reqs);
let res = select_grant(in, low_priority, blocked_in.wget());
let res = select_grant(in, high_prio, blocked_in.wget());
grants <= res.grant_vec;
if (res.granted)
low_priority <= res.selected+1;
if (res.selected == fromInteger(valueOf(num_clients)-1))
high_prio <= 0;
else
high_prio <= res.selected+1;
blocked_out <= res.blocked_addr;
endrule

76
vram/MemArbiter_Test.bsv
View File

@ -227,77 +227,89 @@ module mkTB(Empty);
let rrTests = vec(
// Simple grants
testCase("All idle",
vec(idle, idle, idle), noForbid,
vec(idle, idle, idle, idle), noForbid,
noGrant, noForbid),
testCase("Port 0 read",
vec(read(1), idle, idle), noForbid,
vec(read(1), idle, idle, idle), noForbid,
grant(0), noForbid),
testCase("Port 0 write",
vec(write(1), idle, idle), noForbid,
vec(write(1), idle, idle, idle), noForbid,
grant(0), forbid(1)),
testCase("Port 1 read",
vec(idle, read(1), idle), noForbid,
vec(idle, read(1), idle, idle), noForbid,
grant(1), noForbid),
testCase("Port 1 write",
vec(idle, write(1), idle), noForbid,
vec(idle, write(1), idle, idle), noForbid,
grant(1), forbid(1)),
testCase("Port 2 read",
vec(idle, idle, read(1)), noForbid,
vec(idle, idle, read(1), idle), noForbid,
grant(2), noForbid),
testCase("Port 2 write",
vec(idle, idle, write(1)), noForbid,
vec(idle, idle, write(1), idle), noForbid,
grant(2), forbid(1)),
testCase("Port 3 read",
vec(idle, idle, idle, read(1)), noForbid,
grant(3), noForbid),
testCase("Port 3 write",
vec(idle, idle, idle, write(1)), noForbid,
grant(3), forbid(1)),
// Priorities
testCase("Port 2 to reset RR",
vec(idle, idle, read(1)), noForbid,
grant(2), noForbid),
testCase("Port 3 to reset RR",
vec(idle, idle, idle, read(1)), noForbid,
grant(3), noForbid),
testCase("Port 0+1 #1",
vec(read(1), read(2), idle), noForbid,
vec(read(1), read(2), idle, idle), noForbid,
grant(0), noForbid),
testCase("Port 0+1 #2",
vec(read(1), read(2), idle), noForbid,
vec(read(1), read(2), idle, idle), noForbid,
grant(1), noForbid),
testCase("Port 0+1 #3",
vec(read(1), read(2), idle), noForbid,
vec(read(1), read(2), idle, idle), noForbid,
grant(0), noForbid),
testCase("Port 0+2 #1",
vec(read(1), idle, read(2)), noForbid,
vec(read(1), idle, read(2), idle), noForbid,
grant(2), noForbid),
testCase("Port 0+2 #2",
vec(read(1), idle, read(2)), noForbid,
vec(read(1), idle, read(2), idle), noForbid,
grant(0), noForbid),
testCase("Port 0+1+2 #1",
vec(read(1), read(2), read(3)), noForbid,
testCase("Port 0+1+2+3 #1",
vec(read(1), read(2), read(3), read(4)), noForbid,
grant(1), noForbid),
testCase("Port 0+1+2 #2",
vec(read(1), read(2), read(3)), noForbid,
testCase("Port 0+1+2+3 #2",
vec(read(1), read(2), read(3), read(4)), noForbid,
grant(2), noForbid),
testCase("Port 0+1+2 #3",
vec(read(1), read(2), read(3)), noForbid,
testCase("Port 0+1+2+3 #3",
vec(read(1), read(2), read(3), read(4)), noForbid,
grant(3), noForbid),
testCase("Port 0+1+2+3 #4",
vec(read(1), read(2), read(3), read(4)), noForbid,
grant(0), noForbid),
testCase("Port 0+1+2 #4",
vec(read(1), read(2), read(3)), noForbid,
testCase("Port 0+1+2+3 #5",
vec(read(1), read(2), read(3), read(4)), noForbid,
grant(1), noForbid),
// Forbidden addrs
testCase("Port 2 to reset RR",
vec(idle, idle, read(1)), noForbid,
grant(2), noForbid),
testCase("Port 3 to reset RR",
vec(idle, idle, idle, read(1)), noForbid,
grant(3), noForbid),
testCase("RR with denied writes #1",
vec(read(1), write(2), read(3)), forbid(3),
vec(read(1), write(2), read(3), read(4)), forbid(3),
grant(0), noForbid),
testCase("RR with denied writes #2",
vec(read(1), write(2), read(3)), forbid(3),
vec(read(1), write(2), read(3), read(4)), forbid(3),
grant(1), forbid(2)),
testCase("RR with denied writes #3",
vec(read(1), write(2), read(3)), forbid(3),
grant(0), noForbid),
vec(read(1), write(2), read(3), read(4)), forbid(3),
grant(3), noForbid),
testCase("RR with denied writes #4",
vec(read(1), write(2), read(3)), forbid(3),
vec(read(1), write(2), read(3), read(4)), forbid(3),
grant(0), noForbid),
testCase("RR with denied writes #5",
vec(read(1), write(2), read(3), read(4)), forbid(3),
grant(1), forbid(2))
);
MemArbiter#(3, Addr) rr <- mkRoundRobinMemArbiter();
MemArbiter#(4, Addr) rr <- mkRoundRobinMemArbiter();
let rrTB <- mkArbiterTB(rr, rrTests);
runTest(100,