initial work towards message passing interface

+ As they are currently implemented, grid *may* get stuck if two nodes
  try to send to eachother at the same time, I should probably add in
  some kind of input buffer as well

9 files changed, 354 insertions, 444 deletions

diff --git a/src/clock_domain.c b/src/clock_domain.c
index 6610d8f..74f0f03 100644
--- a/src/clock_domain.c
+++ b/src/clock_domain.c
@@ -20,8 +20,6 @@ struct clock_domain {
 	tick period;
 
 	stat ret;
-
-	mtx_t mtx;
 };
 
 void advance_clock(struct clock_domain *clk)
@@ -41,7 +39,6 @@ struct clock_domain *create_clock_domain(tick period)
 		return NULL;
 
 	clk->period = period;
-	mtx_init(&clk->mtx, mtx_plain);
 	clk->components = vec_create(sizeof(struct component *));
 
 	return clk;
@@ -62,20 +59,12 @@ stat clock_domain_add(struct clock_domain *clk, struct component *component)
 	return OK;
 }
 
-static void update_ret(struct clock_domain *clk, stat ret)
-{
-	if (ret) {
-		mtx_lock(&clk->mtx);
-		clk->ret = ret;
-		mtx_unlock(&clk->mtx);
-	}
-}
-
 static void clocked_component_tick(struct clock_domain *clk,
                                    struct component *component)
 {
-	stat ret = component->clock(component);
-	update_ret(clk, ret);
+	stat r = component->clock(component);
+	if (r)
+		clk->ret = r;
 }
 
 stat clock_domain_tick(struct clock_domain *clk)
diff --git a/src/components/bus/simple_bus.c b/src/components/bus/simple_bus.c
index 218e930..1932419 100644
--- a/src/components/bus/simple_bus.c
+++ b/src/components/bus/simple_bus.c
@@ -1,154 +1,76 @@
 /* SPDX-License-Identifier: copyleft-next-0.3.1 */
 /* Copyright 2023 Kim Kuparinen < kimi.h.kuparinen@gmail.com > */
-
-#include <threads.h>
-#include <inttypes.h>
-#include <stdlib.h>
-
-#include <gran/common.h>
-#include <gran/component.h>
+#include <stdbool.h>
 
 #include <gran/bus/simple_bus.h>
+#include <gran/vec.h>
 
-struct mem_region {
-	uintptr_t addr;
-	size_t size;
+struct bus_region {
+	uint64_t addr;
+	uint64_t size;
 	struct component *component;
-	struct mem_region *next;
 };
 
 struct simple_bus {
 	struct component component;
-	mtx_t lock;
+	struct vec regions;
 
-	struct mem_region *mem_regions;
+	struct component *send;
+	struct packet pkt;
+	bool busy;
 };
 
-static struct mem_region *find_mem_region(struct simple_bus *bus,
-                                          uintptr_t addr)
+static struct bus_region *find_bus_region(struct simple_bus *bus, uint64_t addr)
 {
-	if (!bus->mem_regions)
-		return NULL;
-
-	struct mem_region *cur = bus->mem_regions;
-	while (cur) {
-		/* address is within memory region */
-		if (addr >= cur->addr && addr < cur->addr + cur->size)
-			return cur;
-
-		cur = cur->next;
+	foreach_vec(i, bus->regions) {
+		struct bus_region *r = vec_at(&bus->regions, i);
+		if (addr >= r->addr && addr < (r->addr + r->size))
+			return r;
 	}
 
 	return NULL;
 }
 
-static stat add_mem_region(struct simple_bus *bus, struct mem_region *new)
+static stat simple_bus_clock(struct simple_bus *bus)
 {
-	if (!bus->mem_regions) {
-		bus->mem_regions = new;
-		return OK;
-	}
+	if (bus->busy) {
+		stat r = SEND(bus, bus->send, bus->pkt);
+		if (r == EBUSY)
+			return OK;
 
-	struct mem_region *found = NULL;
-	if ((found = find_mem_region(bus, new->addr))) {
-		error("%s overlaps with %s at %" PRIuPTR,
-		      new->component->name,
-		      found->component->name,
-		      new->addr
-		      );
-		return EEXISTS;
+		bus->busy = false;
+		return r;
 	}
 
-	new->next = bus->mem_regions;
-	bus->mem_regions = new;
 	return OK;
 }
 
-static stat simple_bus_write(struct simple_bus *bus, struct packet *pkt)
-{
-	/* only one device can drive the bus at one time */
-	if (mtx_trylock(&bus->lock) != thrd_success)
-		return EBUSY;
-
-	struct mem_region *mem_region = find_mem_region(bus, packet_addr(pkt));
-	if (!mem_region) {
-		warn("nothing to write on bus %s at %" PRIuPTR,
-		     bus->component.name, packet_addr(pkt));
-		return EBUS;
-	}
-
-	stat ret = write(mem_region->component, pkt);
-
-	mtx_unlock(&bus->lock);
-	return ret;
-}
-
-static stat simple_bus_read(struct simple_bus *bus, struct packet *pkt)
+static stat simple_bus_receive(struct simple_bus *bus, struct component *from, struct packet pkt)
 {
-	/* only one device can drive the bus at one time */
-	if (mtx_trylock(&bus->lock) != thrd_success)
+	if (bus->busy)
 		return EBUSY;
 
-	struct mem_region *mem_region = find_mem_region(bus, packet_addr(pkt));
-	if (!mem_region) {
-		warn("nothing to read on bus %s at %" PRIuPTR,
-		     bus->component.name, packet_addr(pkt));
-		return EBUS;
-	}
+	bus->busy = true;
 
-	stat ret = read(mem_region->component, pkt);
+	struct bus_region *region = find_bus_region(bus, pkt.to);
+	if (!region) {
+		warn("illegal address on bus %s at %" PRIuPTR,
+		     bus->component.name, pkt.to);
 
-	mtx_unlock(&bus->lock);
-	return ret;
-}
-
-static stat simple_bus_swap(struct simple_bus *bus, struct packet *pkt)
-{
-	if (mtx_trylock(&bus->lock) != thrd_success)
-		return EBUSY;
-
-	struct mem_region *mem_region = find_mem_region(bus, packet_addr(pkt));
-	if (!mem_region) {
-		warn("nothing to swap on bus %s at %" PRIuPTR,
-		     bus->component.name, packet_addr(pkt));
-		return EBUS;
-	}
-
-	stat ret = swap(mem_region->component, pkt);
-
-	mtx_unlock(&bus->lock);
-	return ret;
-}
-
-static stat simple_bus_snoop(struct simple_bus *bus, struct snoop *snoop)
-{
-	struct mem_region *cur = bus->mem_regions;
-	while (cur) {
-		if (cur->component->snoop) {
-			stat ret = cur->component->snoop(cur->component, snoop);
-			if (ret)
-				return ret;
-
-			if (snoop_state(snoop) == SNOOP_ANSWERED)
-				return OK;
-		}
-
-		cur = cur->next;
+		bus->send = from;
+		bus->pkt = response(pkt);
+		set_flags(&bus->pkt, PACKET_ERROR);
+		return OK;
 	}
 
+	bus->send = region->component;
+	bus->pkt = pkt;
 	return OK;
 }
 
 static void simple_bus_destroy(struct simple_bus *bus)
 {
-	struct mem_region *cur = bus->mem_regions, *next = NULL;
-	if (cur)
-		do {
-			next = cur->next;
-			destroy(cur->component);
-			free(cur);
-		} while ((cur = next));
-
+	vec_destroy(&bus->regions);
 	free(bus);
 }
 
@@ -158,34 +80,38 @@ struct component *create_simple_bus()
 	if (!bus)
 		return NULL;
 
-	bus->component.write = (write_callback)simple_bus_write;
-	bus->component.read = (read_callback)simple_bus_read;
-	bus->component.swap = (swap_callback)simple_bus_swap;
-	bus->component.snoop = (snoop_callback)simple_bus_snoop;
-	// actually, still not sure about what API I want to use for controls
-	// bus->component.ctrl = (ctrl_callback)simple_bus_ctrl;
+	bus->component.receive = (receive_callback)simple_bus_receive;
+	bus->component.clock = (clock_callback)simple_bus_clock;
 
 	bus->component.destroy = (destroy_callback)simple_bus_destroy;
+	bus->regions = vec_create(sizeof(struct bus_region));
 
-	mtx_init(&bus->lock, mtx_plain);
 	return (struct component *)bus;
 }
 
 stat simple_bus_add(struct component *bus, struct component *component,
                     uint64_t addr, uint64_t size)
 {
-	struct mem_region *new = calloc(1, sizeof(struct mem_region));
-	if (!new)
-		return ENOMEM;
+	struct simple_bus *b = (struct simple_bus *)bus;
+	struct bus_region *found = find_bus_region(b, addr);
+	if (!found)        found = find_bus_region(b, addr + size);
 
-	new->addr = addr;
-	new->size = size;
-	new->component = component;
+	if (found) {
+		error("%s overlaps with %s at %" PRIuPTR,
+		      found->component->name,
+		      component->name,
+		      found->addr
+		      );
 
-	if (add_mem_region((struct simple_bus *)bus, new)) {
-		free(new);
 		return EEXISTS;
 	}
 
+	struct bus_region new = (struct bus_region){
+		.component = component,
+		.addr = addr,
+		.size = size
+	};
+
+	vect_append(struct bus_region, b->regions, &new);
 	return OK;
 }
diff --git a/src/components/cpu/riscv/simple_riscv64.c b/src/components/cpu/riscv/simple_riscv64.c
index be96e60..987838e 100644
--- a/src/components/cpu/riscv/simple_riscv64.c
+++ b/src/components/cpu/riscv/simple_riscv64.c
@@ -9,8 +9,13 @@
 
 #include <gran/cpu/riscv/simple_riscv64.h>
 
-struct simple_rv64_ldst {
-	struct packet *pkt;
+enum ldst_state {
+	LDST_IDLE, LDST_BLOCKED, LDST_SENT, LDST_DONE
+};
+
+struct ldst {
+	struct packet pkt;
+	enum ldst_state state;
 	uint32_t reg;
 	bool u;
 };
@@ -21,8 +26,10 @@ struct simple_riscv64 {
 	struct component *imem;
 	struct component *dmem;
 
-	struct simple_rv64_ldst dls;
-	struct simple_rv64_ldst ils;
+	struct ldst dls;
+	struct ldst ils;
+
+	uint64_t rcv;
 
 	/* have to be careful with x0 */
 	uint64_t regs[32];
@@ -396,25 +403,31 @@ static stat load(struct simple_riscv64 *cpu, union rv_insn insn)
 	/* LH/LHU */
 	case 0b101: u = true; /* fallthrough */
 	case 0b001: size = 2; break;
-	/* LW */
+	/* LW/LWU */
+	case 0b110: u = true; /* fallthrough */
 	case 0b010: size = 4; break;
+	/* LD */
 	case 0b011: size = 8; break;
 	default:
 		error("unknown LOAD width %x", insn.btype.funct3);
 		return ENOSUCH;
 	}
 
-	struct packet *pkt = create_packet(PACKET_READ, addr, size);
-	if (!pkt)
-		return EMEM;
+	struct packet pkt = create_packet(cpu->rcv,
+			addr,
+			size,
+			NULL,
+			PACKET_READ);
 
-	cpu->dls = (struct simple_rv64_ldst){pkt, insn.itype.rd, u};
-	stat ret = read(cpu->dmem, pkt);
-	if (ret)
-		return ret;
+	cpu->dls = (struct ldst){pkt, LDST_SENT, insn.itype.rd, u};
+	stat ret = SEND(cpu, cpu->dmem, pkt);
+	if (ret == EBUSY) {
+		cpu->dls.state = LDST_BLOCKED;
+		ret = OK;
+	}
 
 	cpu->pc += 4;
-	return OK;
+	return ret;
 }
 
 #define STYPE_IMM(insn)                     \
@@ -428,66 +441,58 @@ static stat store(struct simple_riscv64 *cpu, union rv_insn insn)
 	int64_t addr = base + imm;
 
 	uint64_t src = get_reg(cpu, insn.stype.rs2);
+	uint64_t size = 0;
 
 	switch (insn.stype.funct3) {
 	/* SB */
-	case 0b000: {
-		cpu->dls.pkt = create_packet(PACKET_WRITE, addr, 1);
-		*(uint8_t *)packet_data(cpu->dls.pkt) = src;
-		break;
-	}
+	case 0b000: size = 1; break;
 	/* SH */
-	case 0b001: {
-		cpu->dls.pkt = create_packet(PACKET_WRITE, addr, 2);
-		*(uint16_t *)packet_data(cpu->dls.pkt) = src;
-		break;
-	}
+	case 0b001: size = 2; break;
 	/* SW */
-	case 0b010: {
-		cpu->dls.pkt = create_packet(PACKET_WRITE, addr, 4);
-		*(uint32_t *)packet_data(cpu->dls.pkt) = src;
-		break;
-	}
+	case 0b010: size = 4; break;
 	/* SD */
-	case 0b011: {
-		cpu->dls.pkt = create_packet(PACKET_WRITE, addr, 8);
-		*(uint64_t *)packet_data(cpu->dls.pkt) = src;
-		break;
-	}
+	case 0b011: size = 8; break;
 	default:
 		error("unknown width of STORE %x", insn.stype.funct3);
 		return ENOSUCH;
 	}
 
+	struct packet pkt = create_packet(cpu->rcv, addr, size, &src, PACKET_WRITE);
+	cpu->dls = (struct ldst){pkt, LDST_SENT, 0, false};
+	stat ret = SEND(cpu, cpu->dmem, pkt);
+	if (ret == EBUSY) {
+		cpu->dls.state = LDST_BLOCKED;
+		ret = OK;
+	}
+
 	cpu->pc += 4;
-	return write(cpu->dmem, cpu->dls.pkt);
+	return ret;
 }
 
 static void finalize_ld(struct simple_riscv64 *cpu)
 {
-	struct simple_rv64_ldst ld = cpu->dls;
+	struct ldst ld = cpu->dls;
 
 	uint64_t val = 0;
-	void *data = packet_data(ld.pkt);
-	switch (packet_size(ld.pkt)) {
+	switch (packet_convsize(&ld.pkt)) {
 	case 1:
-		if (ld.u) val = *(uint8_t *)data;
-		else val = *(int8_t *)data;
+		if (ld.u) val = packet_convu8(&ld.pkt);
+		else val = packet_convi8(&ld.pkt);
 		break;
 
-	case 2: if (ld.u) val = *(uint16_t *)data;
-		else val = *(int16_t *)data;
+	case 2: if (ld.u) val = packet_convu16(&ld.pkt);
+		else val = packet_convi16(&ld.pkt);
 		break;
 
-	case 4: if (ld.u) val = *(uint32_t *)data;
-		else val = *(int32_t *)data;
+	case 4: if (ld.u) val = packet_convi32(&ld.pkt);
+		else val = packet_convu32(&ld.pkt);
 		break;
 
-	case 8: val = *(uint64_t *)data;
+	case 8: val = packet_convu64(&ld.pkt);
 		break;
 
 	default:
-		error("unknown load size %zu", packet_size(ld.pkt));
+		error("unknown load size %zu", packet_convsize(&ld.pkt));
 	}
 
 	set_reg(cpu, ld.reg, val);
@@ -501,58 +506,97 @@ static void finalize_st(struct simple_riscv64 *cpu)
 
 static void finalize_dls(struct simple_riscv64 *cpu)
 {
-	struct packet *pkt = cpu->dls.pkt;
+	cpu->dls.state = LDST_IDLE;
+	struct packet pkt = cpu->dls.pkt;
 
-	if (packet_type(pkt) == PACKET_READ)
+	if (is_set(&pkt, PACKET_READ))
 		finalize_ld(cpu);
-	else if (packet_type(pkt) == PACKET_WRITE)
+	else if (is_set(&pkt, PACKET_WRITE))
 		finalize_st(cpu);
 	else
 		error("unsupported packet type for simple_riscv64");
-
-	destroy_packet(pkt);
-	cpu->dls.pkt = NULL;
 }
 
 static uint32_t finalize_ils(struct simple_riscv64 *cpu)
 {
-	uint32_t insn = *(uint32_t *)packet_data(cpu->ils.pkt);
-	destroy_packet(cpu->ils.pkt);
-	cpu->ils.pkt = NULL;
-	return insn;
+	cpu->ils.state = LDST_IDLE;
+	return packet_convu32(&cpu->ils.pkt);
+}
+
+static stat simple_riscv64_receive(struct simple_riscv64 *cpu, struct component *from, struct packet pkt)
+{
+	(void)from;
+
+	if (pkt.to == cpu->rcv) {
+		cpu->dls.pkt = pkt;
+		cpu->dls.state = LDST_DONE;
+		return OK;
+	}
+	else if (pkt.to == cpu->rcv + 64) {
+		cpu->ils.pkt = pkt;
+		cpu->ils.state = LDST_DONE;
+		return OK;
+	}
+	else {
+		error("illegal receive on %s", cpu->component.name);
+		return EBUS;
+	}
 }
 
 static stat simple_riscv64_clock(struct simple_riscv64 *cpu)
 {
 	/* there's an active data transfer we should handle */
-	if (cpu->dls.pkt) {
-		assert(packet_state(cpu->dls.pkt) != PACKET_FAILED);
+	if (cpu->dls.state != LDST_IDLE) {
+		assert(!is_set(&cpu->dls.pkt, PACKET_ERROR));
+
+		if (cpu->dls.state == LDST_BLOCKED) {
+			stat r = SEND(cpu, cpu->dmem, cpu->dls.pkt);
+			if (r == EBUSY)
+				return OK;
 
-		if (packet_state(cpu->dls.pkt) == PACKET_DONE)
+			cpu->dls.state = LDST_SENT;
+			return OK;
+		}
+
+		if (cpu->dls.state == LDST_SENT)
+			return OK;
+
+		if (cpu->dls.state == LDST_DONE) {
 			finalize_dls(cpu);
-		else /* wait for data */
+			cpu->dls.state = LDST_IDLE;
+		}
+		else
 			return OK;
 	}
 
-	if (!cpu->ils.pkt) {
-		cpu->ils.pkt =
-			create_packet(PACKET_READ, cpu->pc, sizeof(uint32_t));
-		if (!cpu->ils.pkt)
-			return EMEM;
+	if (cpu->ils.state == LDST_BLOCKED) {
+		stat ret = SEND(cpu, cpu->imem, cpu->ils.pkt);
+		if (ret == EBUSY)
+			return OK;
 
-		stat ret = read(cpu->imem, cpu->ils.pkt);
-		if (ret)
-			return ret;
+		return OK;
 	}
 
 	uint32_t insn = 0;
-	if (cpu->ils.pkt) {
-		assert(packet_state(cpu->ils.pkt) != PACKET_FAILED);
+	if (cpu->ils.state == LDST_DONE) {
+		assert(!is_set(&cpu->dls.pkt, PACKET_ERROR));
 
-		if (packet_state(cpu->ils.pkt) == PACKET_DONE)
-			insn = finalize_ils(cpu);
-		else /* wait for instruction */
-			return OK;
+		insn = finalize_ils(cpu);
+		cpu->ils.state = LDST_IDLE;
+	}
+
+	if (cpu->ils.state == LDST_IDLE) {
+		cpu->ils.pkt = create_packet(cpu->rcv + 64,
+						cpu->pc,
+						sizeof(uint32_t),
+						NULL,
+						PACKET_READ);
+		cpu->ils.state = LDST_SENT;
+		stat ret = SEND(cpu, cpu->imem, cpu->ils.pkt);
+		if (ret == EBUSY) {
+			cpu->ils.state = LDST_BLOCKED;
+			return ret;
+		}
 	}
 
 	// for now assume little endian emulated and host cpu
@@ -586,23 +630,12 @@ static stat simple_riscv64_clock(struct simple_riscv64 *cpu)
 
 static void simple_riscv64_destroy(struct simple_riscv64 *cpu)
 {
-	/* oh yeah, will have to think about the name stuff,
-	 * i.e. how and where to free it, and where to assign it */
 	destroy(cpu->imem);
-
-	if (cpu->imem != cpu->dmem)
-		destroy(cpu->dmem);
-
-	if (cpu->ils.pkt)
-		destroy_packet(cpu->ils.pkt);
-
-	if (cpu->dls.pkt)
-		destroy_packet(cpu->dls.pkt);
-
+	destroy(cpu->dmem);
 	free(cpu);
 }
 
-struct component *create_simple_riscv64(uint32_t start_pc,
+struct component *create_simple_riscv64(uint64_t rcv, uint32_t start_pc,
                                         struct component *imem,
                                         struct component *dmem)
 {
@@ -610,10 +643,12 @@ struct component *create_simple_riscv64(uint32_t start_pc,
 	if (!new)
 		return NULL;
 
+	new->component.receive = (receive_callback)simple_riscv64_receive;
 	new->component.clock = (clock_callback)simple_riscv64_clock;
 	new->component.destroy = (destroy_callback)simple_riscv64_destroy;
 
 	new->pc = start_pc;
+	new->rcv = rcv;
 	new->imem = imem;
 	new->dmem = dmem;
 	return (struct component *)new;
diff --git a/src/components/grid/node.c b/src/components/grid/node.c
index 0aed768..57ef7ed 100644
--- a/src/components/grid/node.c
+++ b/src/components/grid/node.c
@@ -5,73 +5,101 @@
  * Each node should have a router beneath it, just to simplify my life. A router
  * is basically a bus with a fallback ascension path.
  */
+#include <stdbool.h>
+
 #include <gran/grid/node.h>
 
 struct grid_node {
 	struct component component;
 	uint8_t u, v, x, y;
 	struct component *left, *right, *up, *down, *ascend, *lower;
+
+	struct component *send;
+	struct packet pkt;
+	bool busy;
 };
 
-typedef read_callback callback;
+static stat grid_clock(struct grid_node *grid)
+{
+	if (!grid->busy)
+		return OK;
+
+	stat r = SEND(grid, grid->send, grid->pkt);
+	if (r == EBUSY)
+		return OK;
+
+	grid->busy = false;
+	return r;
+}
 
-static stat grid_route(struct grid_node *grid, struct packet *pkt, callback op)
+static stat grid_receive(struct grid_node *grid, struct component *from, struct packet pkt)
 {
-	uint64_t addr = packet_addr(pkt);
-	uint8_t u = (addr >> 56) & 0xff;
-	uint8_t v = (addr >> 48) & 0xff;
-	uint8_t x = (addr >> 40) & 0xff;
-	uint8_t y = (addr >> 32) & 0xff;
+	if (grid->busy)
+		return EBUSY;
 
-	if (grid->u == u && grid->v == v && grid->x == x && grid->y == y)
-		return op(grid->lower, pkt);
+	uint8_t u;
+	uint8_t v;
+	uint8_t x;
+	uint8_t y;
+	uint64_t addr = pkt.to;
+	addr_grid(addr, NULL, &x, &y, &u, &v);
+
+	grid->busy = true;
+	grid->pkt = pkt;
+
+	if (grid->u == u && grid->v == v && grid->x == x && grid->y == y) {
+		if (!grid->lower)
+			goto nosuch;
+
+		grid->send = grid->lower;
+		return OK;
+	}
 
 	if (grid->u != u || grid->v != v) {
 		if (!grid->ascend)
-			return EBUS;
+			goto nosuch;
 
-		return op(grid->ascend, pkt);
+		grid->send = grid->ascend;
+		return OK;
 	}
 
 	if (y < grid->y) {
 		if (!grid->down)
-			return EBUS;
+			goto nosuch;
 
-		return op(grid->down, pkt);
+		grid->send = grid->down;
+		return OK;
 	}
 
 	if (y > grid->y) {
 		if (!grid->up)
-			return EBUS;
+			goto nosuch;
 
-		return op(grid->up, pkt);
+		grid->send = grid->up;
+		return OK;
 	}
 
 	if (x < grid->x) {
 		if (!grid->left)
-			return EBUS;
+			goto nosuch;
 
-		return op(grid->left, pkt);
+		grid->send = grid->left;
+		return OK;
 	}
 
 	if (x > grid->x) {
 		if (!grid->right)
 			return EBUS;
 
-		return op(grid->right, pkt);
+		grid->send = grid->right;
+		return OK;
 	}
 
-	return EBUS;
-}
-
-static stat grid_write(struct grid_node *node, struct packet *pkt)
-{
-	return grid_route(node, pkt, write);
-}
-
-static stat grid_read(struct grid_node *node, struct packet *pkt)
-{
-	return grid_route(node, pkt, read);
+nosuch:
+	grid->send = from;
+	grid->pkt = response(pkt);
+	set_flags(&grid->pkt, PACKET_ERROR);
+	return OK;
 }
 
 struct component *create_grid_node(uint8_t u, uint8_t v, uint8_t x, uint8_t y)
@@ -80,13 +108,12 @@ struct component *create_grid_node(uint8_t u, uint8_t v, uint8_t x, uint8_t y)
 	if (!node)
 		return NULL;
 
+	node->component.receive = (receive_callback)grid_receive;
+	node->component.clock = (clock_callback)grid_clock;
 	node->u = u;
 	node->v = v;
 	node->x = x;
 	node->y = y;
-	node->component.write = (write_callback)grid_write;
-	node->component.read = (read_callback)grid_read;
-
 	return (struct component *)node;
 }
 
diff --git a/src/components/grid/router.c b/src/components/grid/router.c
index bdb05c8..63c4011 100644
--- a/src/components/grid/router.c
+++ b/src/components/grid/router.c
@@ -1,3 +1,6 @@
+#include <stdbool.h>
+
+#include <gran/grid/node.h>
 #include <gran/grid/router.h>
 #include <gran/vec.h>
 
@@ -12,6 +15,10 @@ struct node_router {
 	struct component *ascend;
 	struct vec regions;
 	uint8_t u, v, x, y;
+
+	struct component *send;
+	struct packet pkt;
+	bool busy;
 };
 
 static struct router_region *find_region(struct node_router *router, uint32_t addr)
@@ -26,40 +33,55 @@ static struct router_region *find_region(struct node_router *router, uint32_t ad
 	return NULL;
 }
 
-static stat router_write(struct node_router *router, struct packet *pkt)
+static stat router_clock(struct node_router *router)
 {
-	uint64_t addr = packet_addr(pkt);
-	uint8_t u = (addr >> 56) & 0xff;
-	uint8_t v = (addr >> 48) & 0xff;
-	uint8_t x = (addr >> 40) & 0xff;
-	uint8_t y = (addr >> 32) & 0xff;
+	if (!router->busy)
+		return OK;
 
-	if (router->u != u || router->v != v || router->x != x || router->y != y)
-		return write(router->ascend, pkt);
+	stat r = SEND(router, router->send, router->pkt);
+	if (r == EBUSY)
+		return OK;
 
-	struct router_region *region = find_region(router, addr);
-	if (!region)
-		return write(router->ascend, pkt);
-
-	return write(region->component, pkt);
+	router->busy = false;
+	return OK;
 }
 
-static stat router_read(struct node_router *router, struct packet *pkt)
+static stat router_receive(struct node_router *router, struct component *from, struct packet pkt)
 {
-	uint64_t addr = packet_addr(pkt);
-	uint8_t u = (addr >> 56) & 0xff;
-	uint8_t v = (addr >> 48) & 0xff;
-	uint8_t x = (addr >> 40) & 0xff;
-	uint8_t y = (addr >> 32) & 0xff;
+	if (router->busy)
+		return EBUSY;
+
+	router->busy = true;
 
-	if (router->u != u || router->v != v || router->x != x || router->y != y)
-		return read(router->ascend, pkt);
+	uint64_t addr = pkt.to;
+	uint8_t u;
+	uint8_t v;
+	uint8_t x;
+	uint8_t y;
+	addr_grid(addr, NULL, &x, &y, &u, &v);
+
+	router->pkt = pkt;
+
+	if (router->u != u || router->v != v || router->x != x || router->y != y) {
+		if (!router->ascend)
+			goto nosuch;
+
+		router->send = router->ascend;
+		return OK;
+	}
 
 	struct router_region *region = find_region(router, addr);
 	if (!region)
-		return read(router->ascend, pkt);
+		goto nosuch;
 
-	return read(region->component, pkt);
+	router->send = region->component;
+	return OK;
+
+nosuch:
+	router->send = from;
+	router->pkt = response(pkt);
+	set_flags(&router->pkt, PACKET_ERROR);
+	return OK;
 }
 
 struct component *create_node_router(uint8_t u, uint8_t v, uint8_t x, uint8_t y)
@@ -73,8 +95,8 @@ struct component *create_node_router(uint8_t u, uint8_t v, uint8_t x, uint8_t y)
 	router->x = x;
 	router->y = y;
 
-	router->component.write = (write_callback)router_write;
-	router->component.read = (read_callback)router_read;
+	router->component.receive = (receive_callback)router_receive;
+	router->component.clock = (clock_callback)router_clock;
 	router->regions = vec_create(sizeof(struct router_region));
 
 	return (struct component *)router;
diff --git a/src/components/mem/simple_mem.c b/src/components/mem/simple_mem.c
index bb9dd40..e435ea5 100644
--- a/src/components/mem/simple_mem.c
+++ b/src/components/mem/simple_mem.c
@@ -3,38 +3,57 @@
 
 #include <string.h>
 #include <stdlib.h>
+#include <stdbool.h>
 
 #include <gran/mem/simple_mem.h>
 
 struct simple_mem {
 	struct component component;
+	struct component *send;
+	struct packet pkt;
+	bool busy;
+
 	size_t size;
-	char buf[];
+	uint8_t buf[];
 };
 
-static stat simple_mem_write(struct simple_mem *mem, struct packet *pkt)
+static stat simple_mem_clock(struct simple_mem *mem)
 {
-	uintptr_t offset = packet_addr(pkt) % mem->size;
-	if (offset + packet_size(pkt) > mem->size) {
-		error("write outside memory");
-		return ESIZE;
-	}
+	if (mem->busy)
+		return OK;
+
+	stat r = SEND(mem, mem->send, mem->pkt);
+	if (r == EBUSY)
+		return OK;
 
-	memcpy(mem->buf + offset, packet_data(pkt), packet_size(pkt));
-	packet_set_state(pkt, PACKET_DONE);
+	mem->busy = false;
 	return OK;
 }
 
-static stat simple_mem_read(struct simple_mem *mem, struct packet *pkt)
+static stat simple_mem_receive(struct simple_mem *mem, struct component *from, struct packet pkt)
 {
-	uintptr_t offset = packet_addr(pkt) % mem->size;
-	if (offset + packet_size(pkt) > mem->size) {
+	if (mem->busy)
+		return EBUSY;
+
+	mem->send = from;
+
+	uint64_t offset = pkt.to % mem->size;
+	if (offset >= mem->size) {
 		error("read outside memory");
-		return ESIZE;
+		mem->pkt = response(pkt);
+		set_flags(&mem->pkt, PACKET_ERROR);
+		return OK;
 	}
 
-	memcpy(packet_data(pkt), mem->buf + offset, packet_size(pkt));
-	packet_set_state(pkt, PACKET_DONE);
+	if (is_set(&pkt, PACKET_READ))
+		checked_copyto(&pkt, mem->buf + offset);
+	else if (is_set(&pkt, PACKET_WRITE))
+		checked_copyfrom(&pkt, mem->buf + offset);
+	else
+		abort();
+
+	mem->pkt = response(pkt);
+	set_flags(&mem->pkt, PACKET_DONE);
 	return OK;
 }
 
@@ -45,8 +64,8 @@ struct component *create_simple_mem(size_t size)
 		return NULL;
 
 	new->size = size;
-	new->component.write = (write_callback)simple_mem_write;
-	new->component.read = (read_callback)simple_mem_read;
+	new->component.receive = (receive_callback)simple_mem_receive;
+	new->component.clock = (clock_callback)simple_mem_clock;
 	return (struct component *)new;
 }
 
diff --git a/src/components/uart/simple_uart.c b/src/components/uart/simple_uart.c
index 5c97ccd..1528a70 100644
--- a/src/components/uart/simple_uart.c
+++ b/src/components/uart/simple_uart.c
@@ -3,17 +3,42 @@
 
 struct simple_uart {
 	struct component component;
+
+	struct component *send;
+	struct packet pkt;
+	bool busy;
 };
 
-static stat simple_uart_write(struct simple_uart *uart, struct packet *pkt)
+static stat simple_uart_clock(struct simple_uart *uart)
 {
-	(void)uart;
-	size_t size = packet_size(pkt);
-	if (size != 1)
-		return EBUS;
+	if (!uart->busy)
+		return OK;
+
+	stat r = SEND(uart, uart->send, uart->pkt);
+	if (r == EBUSY)
+		return OK;
+
+	uart->busy = false;
+	return OK;
+}
+
+static stat simple_uart_receive(struct simple_uart *uart, struct component *from, struct packet pkt)
+{
+	if (uart->busy)
+		return EBUSY;
+
+	uart->busy = true;
+	uart->send = from;
+	uart->pkt = response(pkt);
+
+	size_t size = packet_convsize(&pkt);
+	if (size != 1) {
+		set_flags(&uart->pkt, PACKET_ERROR);
+		return OK;
+	}
 
-	putchar(*(uint8_t *)packet_data(pkt));
-	packet_set_state(pkt, PACKET_DONE);
+	putchar(packet_convu8(&pkt));
+	set_flags(&uart->pkt, PACKET_DONE);
 	return OK;
 }
 
@@ -23,6 +48,7 @@ struct component *create_simple_uart()
 	if (!uart)
 		return NULL;
 
-	uart->component.write = (write_callback)simple_uart_write;
+	uart->component.receive = (receive_callback)simple_uart_receive;
+	uart->component.clock = (clock_callback)simple_uart_clock;
 	return (struct component *)uart;
 }
diff --git a/src/packet.c b/src/packet.c
deleted file mode 100644
index 9442307..0000000
--- a/src/packet.c
+++ /dev/null
@@ -1,92 +0,0 @@
-/* SPDX-License-Identifier: copyleft-next-0.3.1 */
-/* Copyright 2023 Kim Kuparinen < kimi.h.kuparinen@gmail.com > */
-
-#include <gran/packet.h>
-#include <stdlib.h>
-#include <assert.h>
-
-struct packet {
-	enum packet_state state;
-	enum packet_type type;
-
-	uintptr_t addr;
-	size_t size;
-	void *data;
-};
-
-
-struct packet *create_packet(enum packet_type type, uintptr_t addr, size_t size)
-{
-	struct packet *pkt = malloc(sizeof(struct packet) + size);
-	if (!pkt)
-		return NULL;
-
-	pkt->state = PACKET_INIT;
-	pkt->type = type;
-	pkt->addr = addr;
-	pkt->size = size;
-	pkt->data = pkt + 1;
-	return pkt;
-}
-
-struct packet *create_packet_with(enum packet_type type, uintptr_t addr,
-                                  size_t size, void *data)
-{
-	struct packet *pkt = malloc(sizeof(struct packet));
-	if (!pkt)
-		return NULL;
-
-	pkt->state = PACKET_INIT;
-	pkt->type = type;
-	pkt->addr = addr;
-	pkt->size = size;
-	pkt->data = data;
-	return pkt;
-}
-
-struct packet *reuse_packet(struct packet *pkt, enum packet_type type,
-                            uintptr_t addr, size_t size, void *data)
-{
-	assert(pkt->state == PACKET_DONE);
-	pkt->state = PACKET_INIT;
-	pkt->type = type;
-	pkt->addr = addr;
-	pkt->size = size;
-	pkt->data = data;
-	return pkt;
-}
-
-enum packet_type packet_type(struct packet *pkt)
-{
-	return pkt->type;
-}
-
-enum packet_state packet_state(struct packet *pkt)
-{
-	return pkt->state;
-}
-
-void packet_set_state(struct packet *pkt, enum packet_state state)
-{
-	pkt->state = state;
-}
-
-size_t packet_size(struct packet *pkt)
-{
-	return pkt->size;
-}
-
-uintptr_t packet_addr(struct packet *pkt)
-{
-	return pkt->addr;
-}
-
-void *packet_data(struct packet *pkt)
-{
-	return pkt->data;
-}
-
-void destroy_packet(struct packet *pkt)
-{
-	free(pkt);
-}
diff --git a/src/snoop.c b/src/snoop.c
deleted file mode 100644
index 23970a8..0000000
--- a/src/snoop.c
+++ /dev/null
@@ -1,42 +0,0 @@
-/* SPDX-License-Identifier: copyleft-next-0.3.1 */
-/* Copyright 2023 Kim Kuparinen < kimi.h.kuparinen@gmail.com > */
-
-#include <stdlib.h>
-
-#include <gran/snoop.h>
-
-struct snoop {
-	enum snoop_state state;
-	uintptr_t addr;
-	size_t size;
-};
-
-struct snoop *create_snoop(uintptr_t addr, size_t size)
-{
-	struct snoop *snoop = calloc(1, sizeof(struct snoop));
-
-	snoop->state = SNOOP_UNANSWERED;
-	snoop->addr = addr;
-	snoop->size = size;
-	return snoop;
-}
-
-enum snoop_state snoop_state(struct snoop *snoop)
-{
-	return snoop->state;
-}
-
-uintptr_t snoop_addr(struct snoop *snoop)
-{
-	return snoop->addr;
-}
-
-size_t snoop_size(struct snoop *snoop)
-{
-	return snoop->size;
-}
-
-void destroy_snoop(struct snoop *snoop)
-{
-	free(snoop);
-}