diff --git a/sys/src/9/imx8/reform b/sys/src/9/imx8/reform
index 52dfa1d5c..ae88c1d99 100644
--- a/sys/src/9/imx8/reform
+++ b/sys/src/9/imx8/reform
@@ -15,7 +15,10 @@ dev
 	ether	netif
 	ip	arp chandial ip ipv6 ipaux iproute netlog nullmedium pktmedium inferno
 	uart
+	usb
+
 link
+	usbxhciimx
 	etherimx	ethermii
 	ethermedium
 	loopbackmedium
diff --git a/sys/src/9/imx8/usbxhciimx.c b/sys/src/9/imx8/usbxhciimx.c
new file mode 100644
index 000000000..e08b80b19
--- /dev/null
+++ b/sys/src/9/imx8/usbxhciimx.c
@@ -0,0 +1,1821 @@
+#include	"u.h"
+#include	"../port/lib.h"
+#include	"mem.h"
+#include	"dat.h"
+#include	"fns.h"
+#include	"io.h"
+#include	"../port/error.h"
+#include	"../port/usb.h"
+
+enum {
+	/* Capability Registers */
+	CAPLENGTH	= 0x00/4,	// 1
+	HCIVERSION	= 0x02/4,	// 2
+	HCSPARAMS1	= 0x04/4,
+	HCSPARAMS2	= 0x08/4,
+	HCSPARAMS3	= 0x0C/4,
+
+	HCCPARAMS	= 0x10/4,
+		AC64	= 1<<0,
+		BNC	= 1<<1,
+		CSZ	= 1<<2,
+		PPC	= 1<<3,
+		PIND	= 1<<4,
+		LHRC	= 1<<5,
+		LTC	= 1<<6,
+		NSS	= 1<<7,
+
+	DBOFF		= 0x14/4,
+	RTSOFF		= 0x18/4,
+
+	HCCPARAMS2	= 0x1C/4,
+
+	/* Operational Registers */
+	USBCMD		= 0x00/4,	/* USB Command Register */
+		RUNSTOP	= 1<<0,		/* Run/Stop - RW */
+		HCRST	= 1<<1,		/* Host Controller Reset - RW */
+		INTE	= 1<<2,		/* Interrupter Enable - RW */
+		HSEE	= 1<<3,		/* Host System Error Enable - RW */
+		LHCRST	= 1<<7,		/* Light Host Controller Reset - RO/RW */
+		CSS	= 1<<8,		/* Controller Save State - RW */
+		CRS	= 1<<9,		/* Controller Restore State - RW */
+		EWE	= 1<<10,	/* Enable Wrap Event - RW */
+		EU3S	= 1<<11,	/* Enable U3 MFINDEX Stop - RW */
+
+	USBSTS		= 0x04/4,	/* USB Status Register */
+		HCH	= 1<<0,		/* HCHalted - RO */
+		HSE	= 1<<2,		/* Host System Error - RW1C */
+		EINT	= 1<<3,		/* Event Interrupt - RW1C */
+		PCD	= 1<<4,		/* Port Change Detect - RW1C */
+		SSS	= 1<<8,		/* Save State Status - RO */
+		RSS	= 1<<9,		/* Restore State Status - RO */
+		SRE	= 1<<10,	/* Save/Restore Error - RW1C */
+		CNR	= 1<<11,	/* Controller Not Ready - RO */
+		HCE	= 1<<12,	/* Host Controller Error - RO */
+
+	PAGESIZE	= 0x08/4,	/* Page Size - RO */
+
+	DNCTRL		= 0x14/4,	/* Device Notification Control Register - RW */
+
+	CRCR		= 0x18/4,	/* Command Ring Control Register - RW */
+		RCS	= 1<<0,		/* Ring Cycle State - RW */
+		CS	= 1<<1,		/* Command Stop - RW1S */
+		CA	= 1<<2,		/* Command Abort - RW1S */
+		CRR	= 1<<3,		/* Command Ring Running - RO */
+
+	DCBAAP		= 0x30/4,	// 8
+
+	CONFIG		= 0x38/4,	/* Configure Register (MaxSlotEn[7:0]) */
+
+	/* Port Register Set */
+	PORTSC		= 0x00/4,	/* Port status and Control Register */
+		CCS	= 1<<0,		/* Current Connect Status - ROS */
+		PED	= 1<<1,		/* Port Enable/Disabled - RW1CS */
+		OCA	= 1<<3,		/* Over-current Active - RO */
+		PR	= 1<<4,		/* Port Reset - RW1S */
+		PLS	= 15<<5,	/* Port Link State - RWS */
+		PP	= 1<<9,		/* Port Power - RWS */
+		PS	= 15<<10,	/* Port Speed - ROS */
+		PIC	= 3<<14,	/* Port Indicator Control - RWS */
+		LWS	= 1<<16,	/* Port Link Write Strobe - RW */
+		CSC	= 1<<17,	/* Connect Status Change - RW1CS */
+		PEC	= 1<<18,	/* Port Enabled/Disabled Change - RW1CS */
+		WRC	= 1<<19,	/* Warm Port Reset Change - RW1CS */
+		OCC	= 1<<20,	/* Over-current Change - RW1CS */
+		PRC	= 1<<21,	/* Port Reset Change - RW1CS */
+		PLC	= 1<<22,	/* Port Link State Change - RW1CS */
+		CEC	= 1<<23,	/* Port Config Error Change - RW1CS */
+		CAS	= 1<<24,	/* Cold Attach Status - RO */
+		WCE	= 1<<25,	/* Wake on Connect Enable - RWS */
+		WDE	= 1<<26,	/* Wake on Disconnect Enable - RWS */
+		WOE	= 1<<27,	/* Wake on Over-current Enable - RWS */
+		DR	= 1<<30,	/* Device Removable - RO */
+		WPR	= 1<<31,	/* Warm Port Reset - RW1S */
+
+	PORTPMSC	= 0x04/4,
+	PORTLI		= 0x08/4,
+
+	/* Host Controller Runtime Register */
+	MFINDEX		= 0x0000/4,	/* Microframe Index */
+	IR0		= 0x0020/4,	/* Interrupt Register Set 0 */
+
+	/* Interrupter Registers */
+	IMAN		= 0x00/4,	/* Interrupter Management */
+	IMOD		= 0x04/4,	/* Interrupter Moderation */
+	ERSTSZ		= 0x08/4,	/* Event Ring Segment Table Size */
+	ERSTBA		= 0x10/4,	/* Event Ring Segment Table Base Address */
+	ERDP		= 0x18/4,	/* Event Ring Dequeue Pointer */
+
+	/* TRB flags */
+	TR_ENT		= 1<<1,
+	TR_ISP		= 1<<2,
+	TR_NS		= 1<<3,
+	TR_CH		= 1<<4,
+	TR_IOC		= 1<<5,
+	TR_IDT		= 1<<6,
+	TR_BEI		= 1<<9,
+	
+	/* TRB types */
+	TR_RESERVED	= 0<<10,
+	TR_NORMAL	= 1<<10,
+	TR_SETUPSTAGE	= 2<<10,
+	TR_DATASTAGE	= 3<<10,
+	TR_STATUSSTAGE	= 4<<10,
+	TR_ISOCH	= 5<<10,
+	TR_LINK		= 6<<10,
+	TR_EVENTDATA	= 7<<10,
+	TR_NOOP		= 8<<10,
+
+	CR_ENABLESLOT	= 9<<10,
+	CR_DISABLESLOT	= 10<<10,
+	CR_ADDRESSDEV	= 11<<10,
+	CR_CONFIGEP	= 12<<10,
+	CR_EVALCTX	= 13<<10,
+	CR_RESETEP	= 14<<10,
+	CR_STOPEP	= 15<<10,
+	CR_SETTRDQP	= 16<<10,
+	CR_RESETDEV	= 17<<10,
+	CR_FORCECMD	= 18<<10,
+	CR_NEGBW	= 19<<10,
+	CR_SETLAT	= 20<<10,
+	CR_GETPORTBW	= 21<<10,
+	CR_FORCEHDR	= 22<<10,
+	CR_NOOP		= 23<<10,
+
+	ER_TRANSFER	= 32<<10,
+	ER_CMDCOMPL	= 33<<10,
+	ER_PORTSC	= 34<<10,
+	ER_BWREQ	= 35<<10,
+	ER_DOORBELL	= 36<<10,
+	ER_HCE		= 37<<10,
+	ER_DEVNOTE	= 38<<10,
+	ER_MFINDEXWRAP	= 39<<10,
+};
+
+typedef struct Ctlr Ctlr;
+typedef struct Wait Wait;
+typedef struct Ring Ring;
+typedef struct Slot Slot;
+typedef struct Epio Epio;
+typedef struct Port Port;
+
+struct Wait
+{
+	Wait	*next;
+	Ring	*ring;
+	u32int	*td;
+	u32int	er[4];
+	Rendez	*z;
+};
+
+struct Ring
+{
+	int	id;
+
+	Slot	*slot;
+
+	u32int	*base;
+
+	u32int	mask;
+	u32int	shift;
+
+	u32int	rp;
+	u32int	wp;
+
+	u32int	*ctx;
+	u32int	*doorbell;
+
+	int	stopped;
+
+	int	*residue;
+	Wait	*pending;
+	Lock;
+};
+
+struct Slot
+{
+	int	id;
+
+	int	confval; // bConfigurationValue of SET_CONFIGURATION
+	int	iface;	// bInterfaceNumber of SET_INTERFACE
+	int	altc;	// bAlternateSetting of SET_INTERFACE
+
+	Ctlr	*ctlr;
+	Udev	*dev;
+
+	u32int	*ibase;
+	u32int	*obase;
+
+	/* endpoint rings */
+	int	nep;
+	Ring	epr[32];
+};
+
+struct Port
+{
+	char	spec[4];
+	int	proto;
+
+	u32int	*reg;
+};
+
+struct Ctlr
+{
+	u32int	*mmio;
+
+	u32int	*opr;	/* operational registers */
+	u32int	*rts;	/* runtime registers */
+	u32int	*dba;	/* doorbell array */
+
+	u64int	*dcba;	/* device context base array */
+
+	u64int	*sba;	/* scratchpad buffer array */
+	void	*sbp;	/* scratchpad buffer pages */
+
+	u32int	*erst[1];	/* event ring segment table */
+	Ring	er[1];		/* event ring segment */
+	Ring	cr[1];		/* command ring segment */
+	QLock	cmdlock;
+
+	u32int	µframe;
+
+	QLock	slotlock;
+	Slot	**slot;		/* slots by slot id */
+	Port	*port;
+	
+	u32int	hccparams;
+
+	int	csz;
+	int	pagesize;
+	int	nscratch;
+	int	nintrs;
+	int	nslots;
+
+	Rendez	recover;	
+	void	*active;
+};
+
+struct Epio
+{
+	QLock;
+
+	Ring	*ring;
+	Block	*b;
+
+	/* iso */
+	u32int	frame;
+	u32int	period;
+	u32int	incr;
+	u32int	tdsz;
+
+	/* isoread */
+	u32int	rp0;
+	u32int	frame0;
+
+	int	nleft;
+};
+
+static char Ebadlen[] = "bad usb request length";
+static char Enotconfig[] = "usb endpoint not configured";
+static char Erecover[] = "xhci controller needs reset";
+
+static char*
+ctlrcmd(Ctlr *ctlr, u32int c, u32int s, u64int p, u32int *er);
+
+static void
+setrptr(u32int *reg, u64int pa)
+{
+	coherence();
+	reg[0] = pa;
+	reg[1] = pa>>32;
+}
+
+static u32int
+µframe(Ctlr *ctlr)
+{
+	u32int µ;
+	do {
+		µ = (ctlr->rts[MFINDEX] & (1<<14)-1) |
+			(ctlr->µframe & ~((1<<14)-1));
+	} while((int)(µ - ctlr->µframe) < 0);
+	return µ;
+}
+
+static void
+freering(Ring *r)
+{
+	if(r == nil)
+		return;
+	if(r->base != nil){
+		dmaflush(0, r->base, 4*4<<r->shift);
+		free(r->base);
+	}
+	if(r->residue != nil)
+		free(r->residue);
+	memset(r, 0, sizeof(*r));
+}
+
+static Ring*
+initring(Ring *r, int shift)
+{
+	r->id = 0;
+	r->ctx = nil;
+	r->slot = nil;
+	r->doorbell = nil;
+	r->pending = nil;
+	r->residue = nil;
+	r->stopped = 0;
+	r->shift = shift;
+	r->mask = (1<<shift)-1;
+	r->rp = r->wp = 0;
+	r->base = mallocalign(4*4<<shift, 64, 0, 64*1024);
+	if(r->base == nil){
+		freering(r);
+		error(Enomem);
+	}
+	dmaflush(1, r->base, 4*4<<shift);
+	return r;
+}
+
+static void
+flushring(Ring *r)
+{
+	Rendez *z;
+	Wait *w;
+
+	while((w = r->pending) != nil){
+		r->pending = w->next;
+		w->next = nil;
+		if((z = w->z) != nil){
+			w->z = nil;
+			wakeup(z);
+		}
+	}
+}
+
+static u64int
+resetring(Ring *r)
+{
+	u64int pa;
+
+	ilock(r);
+	flushring(r);
+	r->rp = r->wp;
+	pa = PADDR(&r->base[4*(r->wp & r->mask)]) | ((~r->wp>>r->shift) & 1);
+	iunlock(r);
+
+	return pa;
+}
+
+static u32int*
+xecp(Ctlr *ctlr, uchar id, u32int *p)
+{
+	u32int x;
+
+	if(p == nil){
+		p = ctlr->mmio;
+		x = ctlr->hccparams>>16;
+	} else {
+		x = (*p>>8) & 255;
+	}
+	while(x != 0){
+		p += x;
+		x = *p;
+		if((x & 255) == id)
+			return p;
+		x >>= 8;
+		x &= 255;
+	}
+	return nil;
+}
+
+static void
+handoff(Ctlr *ctlr)
+{
+	u32int *r;
+	int i;
+
+	if((r = xecp(ctlr, 1, nil)) == nil)
+		return;
+	if(getconf("*noxhcihandoff") == nil){
+		r[0] |= 1<<24;		/* request ownership */
+		for(i = 0; (r[0] & (1<<16)) != 0 && i<100; i++)
+			tsleep(&up->sleep, return0, nil, 10);
+	}
+	/* disable SMI interrupts */
+	r[1] &= 7<<1 | 255<<5 | 7<<17 | 7<<29;
+
+	/* clear BIOS ownership in case of timeout */
+	r[0] &= ~(1<<16);
+}
+
+static void
+shutdown(Hci *hp)
+{
+	Ctlr *ctlr = hp->aux;
+	int i;
+
+	ctlr->opr[USBCMD] = 0;
+	for(i=0; (ctlr->opr[USBSTS] & HCH) == 0 && i < 10; i++)
+		delay(10);
+	intrdisable(hp->irq, hp->interrupt, hp, hp->tbdf, hp->type);
+}
+
+static void
+release(Ctlr *ctlr)
+{
+	int i;
+
+	freering(ctlr->cr);
+	for(i=0; i<nelem(ctlr->er); i++){
+		freering(&ctlr->er[i]);
+		free(ctlr->erst[i]);
+		ctlr->erst[i] = nil;
+	}
+	free(ctlr->port), ctlr->port = nil;
+	free(ctlr->slot), ctlr->slot = nil;
+	free(ctlr->dcba), ctlr->dcba = nil;
+	free(ctlr->sba), ctlr->sba = nil;
+	if(ctlr->sbp != nil){
+		dmaflush(0, ctlr->sbp, ctlr->nscratch*ctlr->pagesize);
+		free(ctlr->sbp);
+		ctlr->sbp = nil;
+	}
+}
+
+static void recover(void *arg);
+
+static void
+init(Hci *hp)
+{
+	Ctlr *ctlr;
+	Port *pp;
+	u32int *x;
+	uchar *p;
+	int i, j;
+
+	ctlr = hp->aux;
+	if(ctlr->mmio[CAPLENGTH] == -1){
+		error("controller vanished");
+	}
+
+	ctlr->opr = &ctlr->mmio[(ctlr->mmio[CAPLENGTH]&0xFF)/4];
+	ctlr->dba = &ctlr->mmio[ctlr->mmio[DBOFF]/4];
+	ctlr->rts = &ctlr->mmio[ctlr->mmio[RTSOFF]/4];
+
+	ctlr->hccparams = ctlr->mmio[HCCPARAMS];
+	handoff(ctlr);
+
+	for(i=0; (ctlr->opr[USBSTS] & CNR) != 0 && i<100; i++)
+		tsleep(&up->sleep, return0, nil, 10);
+
+	ctlr->opr[USBCMD] = HCRST;
+	delay(1);
+	for(i=0; (ctlr->opr[USBSTS] & (CNR|HCH)) != HCH && i<100; i++)
+		tsleep(&up->sleep, return0, nil, 10);
+
+	intrenable(hp->irq, hp->interrupt, hp, hp->tbdf, hp->type);
+
+	if(waserror()){
+		shutdown(hp);
+		release(ctlr);
+		nexterror();
+	}
+
+	ctlr->csz = (ctlr->hccparams & CSZ) != 0;
+	ctlr->pagesize = (ctlr->opr[PAGESIZE] & 0xFFFF) << 12;
+
+	ctlr->nscratch = (ctlr->mmio[HCSPARAMS2] >> 27) & 0x1F | (ctlr->mmio[HCSPARAMS2] >> 16) & 0x3E0;
+	ctlr->nintrs = (ctlr->mmio[HCSPARAMS1] >> 8) & 0x7FF;
+	ctlr->nslots = (ctlr->mmio[HCSPARAMS1] >> 0) & 0xFF;
+
+	hp->highspeed = 1;
+	hp->superspeed = 0;
+	hp->nports = (ctlr->mmio[HCSPARAMS1] >> 24) & 0xFF;
+	ctlr->port = malloc(hp->nports * sizeof(Port));
+	if(ctlr->port == nil)
+		error(Enomem);
+	for(i=0; i<hp->nports; i++)
+		ctlr->port[i].reg = &ctlr->opr[0x400/4 + i*4];
+
+	x = nil;
+	while((x = xecp(ctlr, 2, x)) != nil){
+		i = x[2]&255;
+		j = (x[2]>>8)&255;
+		while(j--){
+			if(i < 1 || i > hp->nports)
+				break;
+			pp = &ctlr->port[i-1];
+			pp->proto = x[0]>>16;
+			memmove(pp->spec, &x[1], 4);
+			if(memcmp(pp->spec, "USB ", 4) == 0 && pp->proto >= 0x0300)
+				hp->superspeed |= 1<<(i-1);
+			i++;
+		}
+	}
+
+	ctlr->slot = malloc((1+ctlr->nslots)*sizeof(ctlr->slot[0]));
+	ctlr->dcba = mallocalign((1+ctlr->nslots)*sizeof(ctlr->dcba[0]), 64, 0, ctlr->pagesize);
+	if(ctlr->slot == nil || ctlr->dcba == nil)
+		error(Enomem);
+	if(ctlr->nscratch != 0){
+		ctlr->sba = mallocalign(ctlr->nscratch*8, 64, 0, ctlr->pagesize);
+		ctlr->sbp = mallocalign(ctlr->nscratch*ctlr->pagesize, ctlr->pagesize, 0, 0);
+		if(ctlr->sba == nil || ctlr->sbp == nil)
+			error(Enomem);
+		for(i=0, p = ctlr->sbp; i<ctlr->nscratch; i++, p += ctlr->pagesize){
+			memset(p, 0, ctlr->pagesize);
+			ctlr->sba[i] = PADDR(p);
+		}
+		dmaflush(1, ctlr->sbp, ctlr->nscratch*ctlr->pagesize);
+		dmaflush(1, ctlr->sba, ctlr->nscratch*8);
+		ctlr->dcba[0] = PADDR(ctlr->sba);
+	} else {
+		ctlr->dcba[0] = 0;
+	}
+	for(i=1; i<=ctlr->nslots; i++)
+		ctlr->dcba[i] = 0;
+
+	ctlr->opr[CONFIG] = (ctlr->opr[CONFIG] & 0xFFFFFC00) | ctlr->nslots;	/* MaxSlotsEn */
+
+	dmaflush(1, ctlr->dcba, (1+ctlr->nslots)*sizeof(ctlr->dcba[0]));
+	setrptr(&ctlr->opr[DCBAAP], PADDR(ctlr->dcba));
+
+	initring(ctlr->cr, 8);		/* 256 entries */
+	ctlr->cr->id = 0;
+	ctlr->cr->doorbell = &ctlr->dba[0];
+	setrptr(&ctlr->opr[CRCR], resetring(ctlr->cr));
+
+	for(i=0; i<ctlr->nintrs; i++){
+		u32int *irs = &ctlr->rts[IR0 + i*8];
+
+		if(i >= nelem(ctlr->er)){
+			irs[ERSTSZ] = 0;	/* disable ring */
+			irs[IMAN] = 1;
+			irs[IMOD] = 0;
+			setrptr(&irs[ERSTBA], 0);
+			setrptr(&irs[ERDP], 0);
+			continue;
+		}
+
+		/* allocate and link into event ring segment table */
+		initring(&ctlr->er[i], 8);	/* 256 entries */
+		ctlr->erst[i] = mallocalign(4*4, 64, 0, 0);
+		if(ctlr->erst[i] == nil)
+			error(Enomem);
+		*((u64int*)ctlr->erst[i]) = PADDR(ctlr->er[i].base);
+		ctlr->erst[i][2] = ctlr->er[i].mask+1;
+		ctlr->erst[i][3] = 0;
+		dmaflush(1, ctlr->erst[i], 4*4);
+
+		irs[ERSTSZ] = 1;	/* just one segment */
+		irs[IMAN] = 3;
+		irs[IMOD] = 0;
+		setrptr(&irs[ERSTBA], PADDR(ctlr->erst[i]));
+		setrptr(&irs[ERDP], PADDR(ctlr->er[i].base) | (1<<3));
+	}
+	poperror();
+
+	ctlr->µframe = 0;
+	ctlr->opr[USBSTS] = ctlr->opr[USBSTS] & (HSE|EINT|PCD|SRE);
+	coherence();
+
+	ctlr->opr[USBCMD] = RUNSTOP|INTE|HSEE|EWE;
+	for(i=0; (ctlr->opr[USBSTS] & (CNR|HCH)) != 0 && i<100; i++)
+		tsleep(&up->sleep, return0, nil, 10);
+
+	kproc("xhcirecover", recover, hp);
+}
+
+static int
+needrecover(void *arg)
+{
+	Ctlr *ctlr = arg;
+	return 	ctlr->er->stopped || 
+		(ctlr->opr[USBSTS] & (HCH|HCE|HSE)) != 0;
+}
+
+static void
+recover(void *arg)
+{
+	Hci *hp = arg;
+	Ctlr *ctlr = hp->aux;
+
+	while(waserror())
+		;
+	while(!needrecover(ctlr))
+		tsleep(&ctlr->recover, needrecover, ctlr, 1000);
+	shutdown(hp);
+
+	/*
+	 * flush all transactions and wait until all devices have
+	 * been detached by usbd.
+	 */
+	for(;;){
+		int i, j, active;
+
+		ilock(ctlr->cr);
+		ctlr->cr->stopped = 1;
+		flushring(ctlr->cr);
+		iunlock(ctlr->cr);
+
+		active = 0;
+		qlock(&ctlr->slotlock);
+		for(i=1; i<=ctlr->nslots; i++){
+			Slot *slot = ctlr->slot[i];
+			if(slot == nil)
+				continue;
+			active++;
+			for(j=0; j < slot->nep; j++){
+				Ring *ring = &slot->epr[j];
+				if(ring->base == nil)
+					continue;
+				ilock(ring);
+				ring->stopped = 1;
+				flushring(ring);
+				iunlock(ring);
+			}
+		}
+		qunlock(&ctlr->slotlock);
+		if(active == 0)
+			break;
+
+		tsleep(&up->sleep, return0, nil, 100);
+	}
+
+	qlock(&ctlr->slotlock);
+	qlock(&ctlr->cmdlock);
+
+	release(ctlr);
+	if(waserror()) {
+		print("xhci recovery failed: %s\n", up->errstr);
+	} else {
+		init(hp);
+		poperror();
+	}
+
+	qunlock(&ctlr->cmdlock);
+	qunlock(&ctlr->slotlock);
+
+	pexit("", 1);
+}
+
+static void
+dump(Hci *)
+{
+}
+
+static void
+queuetd(Ring *r, u32int c, u32int s, u64int p, Wait *w)
+{
+	u32int *td, x;
+
+	x = r->wp++;
+	if((x & r->mask) == r->mask){
+		td = r->base + 4*(x & r->mask);
+		*(u64int*)td = PADDR(r->base);
+		td[2] = 0;
+		td[3] = ((~x>>r->shift)&1) | (1<<1) | TR_LINK;
+		dmaflush(1, td, 4*4);
+		x = r->wp++;
+	}
+	td = r->base + 4*(x & r->mask);
+	if(w != nil){
+		w->er[0] = w->er[1] = w->er[2] = w->er[3] = 0;
+		w->ring = r;
+		w->td = td;
+		w->z = &up->sleep;
+
+		ilock(r);
+		w->next = r->pending;
+		r->pending = w;
+		iunlock(r);
+	}
+	if(r->residue != nil)
+		r->residue[x & r->mask] = s;
+	coherence();
+	*(u64int*)td = p;
+	td[2] = s;
+	td[3] = ((~x>>r->shift)&1) | c;
+	dmaflush(1, td, 4*4);
+}
+
+static char *ccerrtab[] = {
+[2]	"Data Buffer Error",
+[3]	"Babble Detected Error",
+[4]	"USB Transaction Error",
+[5]	"TRB Error",
+[6]	"Stall Error",
+[7]	"Resume Error",
+[8]	"Bandwidth Error",
+[9]	"No Slots Available",
+[10]	"Invalid Stream Type",
+[11]	"Slot Not Enabled",
+[12]	"Endpoint Not Enabled",
+[13]	"Short Packet",
+[14]	"Ring Underrun",
+[15]	"Ring Overrun",
+[16]	"VF Event Ring Full",
+[17]	"Parameter Error",
+[18]	"Bandwidth Overrun Error",
+[19]	"Context State Error",
+[20]	"No Ping Response",
+[21]	"Event Ring Full",
+[22]	"Incompatible Device",
+[23]	"Missed Service Error",
+[24]	"Command Ring Stopped",
+[25]	"Command Aborted",
+[26]	"Stopped",
+[27]	"Stoppe - Length Invalid",
+[29]	"Max Exit Latency Too Large",
+[31]	"Isoch Buffer Overrun",
+[32]	"Event Lost Error",
+[33]	"Undefined Error",
+[34]	"Invalid Stream ID",
+[35]	"Secondary Bandwidth Error",
+[36]	"Split Transaction Error",
+};
+
+static char*
+ccerrstr(u32int cc)
+{
+	char *s;
+
+	if(cc == 1 || cc == 13)
+		return nil;
+	if(cc < nelem(ccerrtab) && ccerrtab[cc] != nil)
+		s = ccerrtab[cc];
+	else
+		s = "???";
+	return s;
+}
+
+static int
+waitdone(void *a)
+{
+	return ((Wait*)a)->z == nil;
+}
+
+static char*
+waittd(Ctlr *ctlr, Wait *w, int tmout)
+{
+	Ring *r = w->ring;
+
+	coherence();
+	*r->doorbell = r->id;
+
+	while(waserror()){
+		if(r->stopped) {
+			ctlr->er->stopped = 1;
+			wakeup(&ctlr->recover);
+
+			/* wait for rescue */
+			tmout = 0;
+			continue;
+		}
+
+		if(r == ctlr->cr)
+			ctlr->opr[CRCR] |= CA;
+		else
+			ctlrcmd(ctlr, CR_STOPEP | (r->id<<16) | (r->slot->id<<24), 0, 0, nil);
+		r->stopped = 1;
+
+		/* time to abort the transaction */
+		tmout = 5000;
+	}
+	if(tmout > 0){
+		tsleep(&up->sleep, waitdone, w, tmout);
+		if(!waitdone(w))
+			error("timed out");
+	} else {
+		while(!waitdone(w))
+			sleep(&up->sleep, waitdone, w);
+	}
+	poperror();
+	return ccerrstr(w->er[2]>>24);
+}
+
+static char*
+ctlrcmd(Ctlr *ctlr, u32int c, u32int s, u64int p, u32int *er)
+{
+	Wait w[1];
+	char *err;
+
+	qlock(&ctlr->cmdlock);
+	if(needrecover(ctlr)){
+		qunlock(&ctlr->cmdlock);
+		return Erecover;
+	}
+	ctlr->cr->stopped = 0;
+	queuetd(ctlr->cr, c, s, p, w);
+	err = waittd(ctlr, w, 5000);
+	qunlock(&ctlr->cmdlock);
+
+	if(er != nil)
+		memmove(er, w->er, 4*4);
+
+	return err;
+}
+
+static void
+completering(Ring *r, u32int *er)
+{
+	Wait *w, **wp;
+	u32int *td, x;
+	u64int pa;
+
+	pa = (*(u64int*)er) & ~15ULL;
+	ilock(r);
+
+	for(x = r->rp; (int)(r->wp - x) > 0; x++){
+		td = &r->base[4*(x & r->mask)];
+		if((u64int)PADDR(td) == pa){
+			if(r->residue != nil)
+				r->residue[x & r->mask] = er[2] & 0xFFFFFF;
+			r->rp = x+1;
+			break;
+		}
+	}
+
+	wp = &r->pending;
+	while(w = *wp){
+		if((u64int)PADDR(w->td) == pa){
+			Rendez *z = w->z;
+
+			memmove(w->er, er, 4*4);
+			*wp = w->next;
+			w->next = nil;
+
+			if(z != nil){
+				w->z = nil;
+				wakeup(z);
+			}
+			break;
+		} else {
+			wp = &w->next;
+		}
+	}
+
+	iunlock(r);
+}
+
+static void
+interrupt(Ureg*, void *arg)
+{
+	Hci *hp = arg;
+	Ctlr *ctlr = hp->aux;
+	Ring *ring = ctlr->er;
+	Slot *slot;
+	u32int *irs, *td, x;
+
+	if(ring->base == nil)
+		return;
+
+	irs = &ctlr->rts[IR0];
+	x = irs[IMAN];
+	if(x & 1) irs[IMAN] = x & 3;
+
+	for(x = ring->rp;; x=++ring->rp){
+		td = ring->base + 4*(x & ring->mask);
+		dmaflush(0, td, 4*4);
+
+		if((((x>>ring->shift)^td[3])&1) == 0)
+			break;
+
+		switch(td[3] & 0xFC00){
+		case ER_CMDCOMPL:
+			completering(ctlr->cr, td);
+			break;
+		case ER_TRANSFER:
+			x = td[3]>>24;
+			if(x == 0 || x > ctlr->nslots)
+				break;
+			slot = ctlr->slot[x];
+			if(slot == nil)
+				break;
+			completering(&slot->epr[(td[3]>>16)-1&31], td);
+			break;
+		case ER_MFINDEXWRAP:
+			ctlr->µframe = (ctlr->rts[MFINDEX] & (1<<14)-1) | 
+				(ctlr->µframe+(1<<14) & ~((1<<14)-1));
+			break;
+		case ER_HCE:
+			iprint("xhci: host controller error: %ux %ux %ux %ux\n",
+				td[0], td[1], td[2], td[3]);
+			ctlr->er->stopped = 1;
+			wakeup(&ctlr->recover);
+			return;
+		case ER_PORTSC:
+			break;
+		case ER_BWREQ:
+		case ER_DOORBELL:
+		case ER_DEVNOTE:
+		default:
+			iprint("xhci: event %ud: %ux %ux %ux %ux\n",
+				x, td[0], td[1], td[2], td[3]);
+		}
+	}
+
+	setrptr(&irs[ERDP], PADDR(td) | (1<<3));
+}
+
+static void
+freeslot(void *arg)
+{
+	Slot *slot;
+
+	if(arg == nil)
+		return;
+	slot = arg;
+	if(slot->id != 0){
+		Ctlr *ctlr = slot->ctlr;
+		qlock(&ctlr->slotlock);
+		if(ctlr->slot != nil && ctlr->slot[slot->id] == slot){
+			ctlrcmd(ctlr, CR_DISABLESLOT | (slot->id<<24), 0, 0, nil);
+			dmaflush(0, slot->obase, 32*32 << ctlr->csz);
+			ctlr->dcba[slot->id] = 0;
+			dmaflush(1, &ctlr->dcba[slot->id], sizeof(ctlr->dcba[0]));
+			ctlr->slot[slot->id] = nil;
+		}
+		qunlock(&ctlr->slotlock);
+	}
+	freering(&slot->epr[0]);
+	free(slot->ibase);
+	free(slot->obase);
+	free(slot);
+}
+
+static Slot*
+allocslot(Ctlr *ctlr, Udev *dev)
+{
+	u32int r[4];
+	Slot *slot;
+	char *err;
+
+	slot = malloc(sizeof(Slot));
+	if(slot == nil)
+		error(Enomem);
+
+	slot->ctlr = ctlr;
+	slot->dev = dev;
+	slot->nep = 0;
+	slot->id = 0;
+
+	slot->confval = 0;
+	slot->iface = 0;
+	slot->altc = 0;
+
+	qlock(&ctlr->slotlock);
+	if(waserror()){
+		qunlock(&ctlr->slotlock);
+		freeslot(slot);
+		nexterror();
+	}
+	if(ctlr->slot == nil)
+		error(Erecover);
+	slot->ibase = mallocalign(32*33 << ctlr->csz, 64, 0, ctlr->pagesize);
+	slot->obase = mallocalign(32*32 << ctlr->csz, 64, 0, ctlr->pagesize);
+	if(slot->ibase == nil || slot->obase == nil)
+		error(Enomem);
+
+	if((err = ctlrcmd(ctlr, CR_ENABLESLOT, 0, 0, r)) != nil)
+		error(err);
+	slot->id = r[3]>>24;
+	if(slot->id <= 0 || slot->id > ctlr->nslots || ctlr->slot[slot->id] != nil){
+		slot->id = 0;
+		error("bad slot id from controller");
+	}
+	poperror();
+
+	dmaflush(1, slot->obase, 32*32 << ctlr->csz);
+	ctlr->dcba[slot->id] = PADDR(slot->obase);
+	dmaflush(1, &ctlr->dcba[slot->id], sizeof(ctlr->dcba[0]));
+
+	ctlr->slot[slot->id] = slot;
+
+	qunlock(&ctlr->slotlock);
+
+	return slot;
+}
+
+static void
+setdebug(Hci *, int)
+{
+}
+
+static void
+epclose(Ep *ep)
+{
+	Ctlr *ctlr;
+	Slot *slot;
+	Ring *ring;
+	Epio *io;
+
+	if(ep->dev->isroot)
+		return;
+
+	io = ep->aux;
+	if(io == nil)
+		return;
+	ep->aux = nil;
+
+	ctlr = ep->hp->aux;
+	slot = ep->dev->aux;
+
+	if(ep->nb > 0 && (io[OREAD].ring != nil || io[OWRITE].ring != nil)){
+		u32int *w;
+
+		/* input control context */
+		w = slot->ibase;
+		memset(w, 0, 32<<ctlr->csz);
+		w[1] = 1;
+		if((ring = io[OREAD].ring) != nil){
+			w[0] |= 1 << ring->id;
+			if(ring->id == slot->nep)
+				slot->nep--;
+			ctlrcmd(ctlr, CR_STOPEP | (ring->id<<16) | (slot->id<<24), 0, 0, nil);
+		}
+		if((ring = io[OWRITE].ring) != nil){
+			w[0] |= 1 << ring->id;
+			if(ring->id == slot->nep)
+				slot->nep--;
+			ctlrcmd(ctlr, CR_STOPEP | (ring->id<<16) | (slot->id<<24), 0, 0, nil);
+		}
+
+		/* (input) slot context */
+		w += 8<<ctlr->csz;
+		w[0] = (w[0] & ~(0x1F<<27)) | slot->nep<<27;
+
+		/* (input) ep context */
+		w += (ep->nb&Epmax)*2*8<<ctlr->csz;
+		memset(w, 0, 2*32<<ctlr->csz);
+
+		dmaflush(1, slot->ibase, 32*33 << ctlr->csz);
+		ctlrcmd(ctlr, CR_CONFIGEP | (slot->id<<24), 0, PADDR(slot->ibase), nil);
+		dmaflush(0, slot->obase, 32*32 << ctlr->csz);
+
+		freering(io[OREAD].ring);
+		freering(io[OWRITE].ring);
+	}
+	freeb(io[OREAD].b);
+	freeb(io[OWRITE].b);
+	free(io);
+}
+
+static void
+initepctx(u32int *w, Ring *r, Ep *ep)
+{
+	int ival;
+
+	if(ep->dev->speed == Lowspeed || ep->dev->speed == Fullspeed){
+		for(ival=3; ival < 11 && (1<<ival) < ep->pollival; ival++)
+			;
+	} else {
+		for(ival=0; ival < 15 && (1<<ival) < ep->pollival; ival++)
+			;
+	}
+	w[0] = ival<<16;
+	w[1] = ((ep->ttype-Tctl) | (r->id&1)<<2)<<3 | (ep->ntds-1)<<8 | ep->maxpkt<<16;
+	if(ep->ttype != Tiso)
+		w[1] |= 3<<1;
+	*((u64int*)&w[2]) = PADDR(r->base) | 1;
+	w[4] = 2*ep->maxpkt;
+	if(ep->ttype == Tintr || ep->ttype == Tiso)
+		w[4] |= (ep->maxpkt*ep->ntds)<<16;
+}
+
+static void
+initisoio(Epio *io, Ep *ep)
+{
+	if(io->ring == nil)
+		return;
+	io->rp0 = io->ring->wp;
+	io->frame0 = io->frame = 0;
+	io->period = ep->pollival << 3*(ep->dev->speed == Fullspeed || ep->dev->speed == Lowspeed);
+	if(io->ring->id & 1){
+		io->ring->residue = smalloc((io->ring->mask+1)*sizeof(io->ring->residue[0]));
+		io->incr = 0;
+		io->tdsz = ep->maxpkt*ep->ntds;
+	} else {
+		io->incr = ((vlong)ep->hz*ep->pollival<<8)/1000;
+		io->tdsz = (io->incr+255>>8)*ep->samplesz;
+	}
+	io->b = allocb((io->ring->mask+1)*io->tdsz);
+}
+
+static void
+initep(Ep *ep)
+{
+	Epio *io;
+	Ctlr *ctlr;
+	Slot *slot;
+	Ring *ring;
+	u32int *w;
+	char *err;
+
+	io = ep->aux;
+	ctlr = ep->hp->aux;
+	slot = ep->dev->aux;
+
+	io[OREAD].ring = io[OWRITE].ring = nil;
+	if(ep->nb == 0){
+		io[OWRITE].ring = &slot->epr[0];
+		return;
+	}
+
+	/* (input) control context */
+	w = slot->ibase;
+	memset(w, 0, 32<<ctlr->csz);
+	w[1] = 1;
+	w[31] = slot->altc<<16 | slot->iface<<8 | slot->confval;
+
+	if(waserror()){
+		freering(io[OWRITE].ring), io[OWRITE].ring = nil;
+		freering(io[OREAD].ring), io[OREAD].ring = nil;
+		nexterror();
+	}
+	if(ep->mode != OREAD){
+		ring = initring(io[OWRITE].ring = &slot->epr[(ep->nb&Epmax)*2-1], 8);
+		ring->id = (ep->nb&Epmax)*2;
+		if(ring->id > slot->nep)
+			slot->nep = ring->id;
+		ring->slot = slot;
+		ring->doorbell = &ctlr->dba[slot->id];
+		ring->ctx = &slot->obase[ring->id*8<<ctlr->csz];
+		w[1] |= 1 << ring->id;
+	}
+	if(ep->mode != OWRITE){
+		ring = initring(io[OREAD].ring = &slot->epr[(ep->nb&Epmax)*2], 8);
+		ring->id = (ep->nb&Epmax)*2+1;
+		if(ring->id > slot->nep)
+			slot->nep = ring->id;
+		ring->slot = slot;
+		ring->doorbell = &ctlr->dba[slot->id];
+		ring->ctx = &slot->obase[ring->id*8<<ctlr->csz];
+		w[1] |= 1 << ring->id;
+	}
+
+	/* (input) slot context */
+	w += 8<<ctlr->csz;
+	w[0] = (w[0] & ~(0x1F<<27)) | slot->nep<<27;
+	if(!ep->dev->ishub)
+		w[0] &= ~(1<<25);	// MTT
+
+	/* (input) ep context */
+	w += (ep->nb&Epmax)*2*8<<ctlr->csz;
+	if(io[OWRITE].ring != nil){
+		memset(w, 0, 5*4);
+		initepctx(w, io[OWRITE].ring, ep);
+	}
+
+	w += 8<<ctlr->csz;
+	if(io[OREAD].ring != nil){
+		memset(w, 0, 5*4);
+		initepctx(w, io[OREAD].ring, ep);
+	}
+
+	dmaflush(1, slot->ibase, 32*33 << ctlr->csz);
+	err = ctlrcmd(ctlr, CR_CONFIGEP | (slot->id<<24), 0, PADDR(slot->ibase), nil);
+	dmaflush(0, slot->obase, 32*32 << ctlr->csz);
+	if(err != nil)
+		error(err);
+
+	if(ep->ttype == Tiso){
+		initisoio(io+OWRITE, ep);
+		initisoio(io+OREAD, ep);
+	}
+	poperror();
+}
+
+static int
+speedid(int speed)
+{
+	switch(speed){
+	case Fullspeed:		return 1;
+	case Lowspeed:		return 2;
+	case Highspeed:		return 3;
+	case Superspeed:	return 4;
+	}
+	return 0;
+}
+
+static void
+epopen(Ep *ep)
+{
+	Ctlr *ctlr = ep->hp->aux;
+	Slot *slot, *hub;
+	Ring *ring;
+	Epio *io;
+	Udev *dev;
+	char *err;
+	u32int *w;
+	int i;
+
+	if(ep->dev->isroot)
+		return;
+	if(needrecover(ctlr))
+		error(Erecover);
+	io = malloc(sizeof(Epio)*2);
+	if(io == nil)
+		error(Enomem);
+	ep->aux = io;
+	if(waserror()){
+		epclose(ep);
+		nexterror();
+	}
+	dev = ep->dev;
+	slot = dev->aux;
+	if(slot != nil && slot->dev == dev){
+		initep(ep);
+		poperror();
+		return;
+	}
+
+	/* first open has to be control endpoint */
+	if(ep->nb != 0)
+		error(Egreg);
+
+	slot = allocslot(ctlr, dev);
+	if(waserror()){
+		freeslot(slot);
+		nexterror();
+	}
+
+	/* allocate control ep 0 ring */
+	ring = initring(io[OWRITE].ring = &slot->epr[0], 4);
+	ring->id = 1;
+	slot->nep = 1;
+	ring->slot = slot;
+	ring->doorbell = &ctlr->dba[slot->id];
+	ring->ctx = &slot->obase[8<<ctlr->csz];
+
+	/* (input) control context */
+	w = slot->ibase;
+	memset(w, 0, 3*32<<ctlr->csz);
+	w[1] = 3;	/* A0, A1 */
+		
+	/* (input) slot context */
+	w += 8<<ctlr->csz;
+	w[2] = w[3] = 0;
+	w[0] = dev->routestr | speedid(dev->speed)<<20 |
+		(dev->speed == Highspeed && dev->ishub != 0)<<25 |	// MTT
+		(dev->ishub != 0)<<26 | slot->nep<<27;
+	w[1] = dev->rootport<<16;
+
+	/* find the parent hub that this device is conected to */
+	qlock(&ctlr->slotlock);
+	for(i=1; i<=ctlr->nslots; i++){
+		hub = ctlr->slot[i];
+		if(hub == nil || hub->dev == nil || hub->dev->aux != hub)
+			continue;
+		if(hub == slot || hub->dev == dev)
+			continue;
+		if(!hub->dev->ishub)
+			continue;
+		if(hub->dev->addr != dev->hub)
+			continue;
+		if(hub->dev->rootport != dev->rootport)
+			continue;
+
+		if(dev->speed < Highspeed && hub->dev->speed == Highspeed){
+			w[0] |= 1<<25;	// MTT
+			w[2] = hub->id | dev->port<<8;
+		}
+		break;
+	}
+	qunlock(&ctlr->slotlock);
+
+	/* (input) ep context 0 */
+	w += 8<<ctlr->csz;
+	initepctx(w, io[OWRITE].ring, ep);
+
+	dmaflush(1, slot->ibase, 32*33 << ctlr->csz);
+	err = ctlrcmd(ctlr, CR_ADDRESSDEV | (slot->id<<24), 0, PADDR(slot->ibase), nil);
+	dmaflush(0, slot->obase, 32*32 << ctlr->csz);
+	if(err != nil)
+		error(err);
+
+	/* (output) slot context */
+	w = slot->obase;
+
+	dev->addr = w[3] & 0xFF;
+
+	dev->aux = slot;
+	dev->free = freeslot;
+
+	poperror();
+	poperror();
+}
+
+static long
+isoread(Ep *ep, uchar *p, long n)
+{
+	uchar *s, *d;
+	Ctlr *ctlr;
+	Epio *io;
+	u32int i, µ;
+	long m;
+
+	s = p;
+
+	io = (Epio*)ep->aux + OREAD;
+	qlock(io);
+	if(waserror()){
+		qunlock(io);
+		nexterror();
+	}
+	µ = io->period;
+	ctlr = ep->hp->aux;
+Again:
+	if(needrecover(ctlr))
+		error(Erecover);
+
+	for(i = io->frame0; (int)(io->ring->rp - io->rp0) > 0 && n > 0; i++) {
+		if((io->rp0 & io->ring->mask) == io->ring->mask)
+			io->rp0++;
+		m = io->tdsz - io->ring->residue[io->rp0 & io->ring->mask];
+		if(m > 0){
+			d = io->b->rp + (i&io->ring->mask)*io->tdsz;
+			d += io->nleft, m -= io->nleft;
+			if(n < m){
+				dmaflush(0, d, n);
+				memmove(p, d, n);
+				io->nleft += n;
+				p += n;
+				n = 0;
+				break;
+			}
+			dmaflush(0, d, m);
+			memmove(p, d, m);
+			p += m, n -= m;
+
+			if(ep->uframes == 1)
+				n = 0;
+		}
+		io->nleft = 0;
+		io->rp0++;
+	}
+	io->frame0 = i;
+
+	for(i = io->frame;; i++){
+		m = (int)(io->ring->wp - io->rp0);
+		if(m <= 0) {
+			i = (80 + µframe(ctlr))/µ;
+			io->frame0 = i;
+			io->rp0 = io->ring->wp;
+			io->nleft = 0;
+		} else if(m+1 >= io->ring->mask)
+			break;
+		m = io->tdsz;
+		d = io->b->rp + (i&io->ring->mask)*io->tdsz;
+		dmaflush(1, d, m);
+		queuetd(io->ring, TR_ISOCH | (i*µ/8 & 0x7ff)<<20 | TR_IOC, m, PADDR(d), nil);
+	}
+	io->frame = i;
+
+	*io->ring->doorbell = io->ring->id;
+	if(p == s){
+		tsleep(&up->sleep, return0, nil, 5);
+		goto Again;
+	}
+	qunlock(io);
+	poperror();
+
+	return p - s;
+}
+
+static long
+isowrite(Ep *ep, uchar *p, long n)
+{
+	uchar *s, *d;
+	Ctlr *ctlr;
+	Epio *io;
+	u32int i, µ;
+	long m;
+
+	s = p;
+	io = (Epio*)ep->aux + OWRITE;
+	qlock(io);
+	if(waserror()){
+		qunlock(io);
+		nexterror();
+	}
+	µ = io->period;
+	ctlr = ep->hp->aux;
+
+	for(i = io->frame;; i++){
+		for(;;){
+			if(needrecover(ctlr))
+				error(Erecover);
+			m = (int)(io->ring->wp - io->ring->rp);
+			if(m <= 0)
+				i = (80 + µframe(ctlr))/µ;
+			if(m+1 < io->ring->mask)
+				break;
+
+			*io->ring->doorbell = io->ring->id;
+			tsleep(&up->sleep, return0, nil, 5);
+		}
+		m = ((io->incr + (i*io->incr&255))>>8)*ep->samplesz;
+		d = io->b->rp + (i&io->ring->mask)*io->tdsz;
+		m -= io->nleft, d += io->nleft;
+		if(n < m){
+			memmove(d, p, n);
+			p += n;
+			io->nleft += n;
+			break;
+		}
+		memmove(d, p, m);
+		p += m, n -= m;
+		m += io->nleft, d -= io->nleft;
+		io->nleft = 0;
+		dmaflush(1, d, m);
+		queuetd(io->ring, TR_ISOCH | (i*µ/8 & 0x7ff)<<20 | TR_IOC, m, PADDR(d), nil);
+	}
+	io->frame = i;
+
+	while(io->ring->rp != io->ring->wp){
+		int d = (int)(i*µ - µframe(ctlr))/8;
+		d -= ep->sampledelay*1000 / ep->hz;
+		if(d < 5)
+			break;
+
+		*io->ring->doorbell = io->ring->id;
+		tsleep(&up->sleep, return0, nil, d);
+		if(needrecover(ctlr))
+			error(Erecover);
+	}
+
+	qunlock(io);
+	poperror();
+
+	return p - s;
+}
+
+static char*
+unstall(Ep *ep, Ring *r)
+{
+	char *err;
+
+	switch(r->ctx[0]&7){
+	case 2:	/* halted */
+	case 4:	/* error */
+		ep->clrhalt = 1;
+	}
+	if(ep->clrhalt){
+		ep->clrhalt = 0;
+		err = ctlrcmd(r->slot->ctlr, CR_RESETEP | (r->id<<16) | (r->slot->id<<24), 0, 0, nil);
+		dmaflush(0, r->ctx, 8*4 << r->slot->ctlr->csz);
+		if(err != nil)
+			return err;
+		r->stopped = 1;
+	}
+	if(r->stopped){
+		err = ctlrcmd(r->slot->ctlr, CR_SETTRDQP | (r->id<<16) | (r->slot->id<<24), 0, resetring(r), nil);
+		dmaflush(0, r->ctx, 8*4 << r->slot->ctlr->csz);
+		if(err != nil)
+			return err;
+		r->stopped = 0;
+	}
+	if(r->wp - r->rp >= r->mask)
+		return "Ring Full";
+	return nil;
+}
+
+static long
+epread(Ep *ep, void *va, long n)
+{
+	Epio *io;
+	Ctlr *ctlr;
+	uchar *p;
+	char *err;
+	Wait w[1];
+
+	if(ep->dev->isroot)
+		error(Egreg);
+
+	p = va;
+	if(ep->ttype == Tctl){
+		io = (Epio*)ep->aux + OREAD;
+		qlock(io);
+		if(io->b == nil || BLEN(io->b) == 0){
+			qunlock(io);
+			return 0;
+		}
+		if(n > BLEN(io->b))
+			n = BLEN(io->b);
+		memmove(p, io->b->rp, n);
+		io->b->rp += n;
+		qunlock(io);
+		return n;
+	} else if(ep->ttype == Tiso)
+		return isoread(ep, p, n);
+
+	if((uintptr)p <= KZERO){
+		Block *b;
+
+		b = allocb(n);
+		if(waserror()){
+			freeb(b);
+			nexterror();
+		}
+		n = epread(ep, b->rp, n);
+		memmove(p, b->rp, n);
+		freeb(b);
+		poperror();
+		return n;
+	}
+
+	ctlr = (Ctlr*)ep->hp->aux;
+	io = (Epio*)ep->aux + OREAD;
+	qlock(io);
+	if(waserror()){
+		dmaflush(0, io->ring->ctx, 8*4 << ctlr->csz);
+		qunlock(io);
+		nexterror();
+	}
+
+	if((err = unstall(ep, io->ring)) != nil)
+		error(err);
+
+	dmaflush(1, p, n);
+	queuetd(io->ring, TR_NORMAL | TR_IOC, n, PADDR(p), w);
+	err = waittd(ctlr, w, ep->tmout);
+	dmaflush(0, p, n);
+	if(err != nil)
+		error(err);
+
+	qunlock(io);
+	poperror();
+
+	n -= (w->er[2] & 0xFFFFFF);
+	if(n < 0)
+		n = 0;
+
+	return n;
+}
+
+static long
+epwrite(Ep *ep, void *va, long n)
+{
+	Wait w[3];
+	Ctlr *ctlr;
+	Epio *io;
+	uchar *p;
+	char *err;
+
+	if(ep->dev->isroot)
+		error(Egreg);
+
+	p = va;
+	if(ep->ttype == Tctl){
+		int dir, len;
+		Ring *ring;
+		Slot *slot;
+
+		if(n < 8)
+			error(Eshort);
+
+		if(p[0] == 0x00 && p[1] == 0x05)
+			return n;
+
+		ctlr = (Ctlr*)ep->hp->aux;
+		io = (Epio*)ep->aux + OREAD;
+		ring = io[OWRITE-OREAD].ring;
+		slot = ring->slot;
+		qlock(io);
+		if(waserror()){
+			ilock(ring);
+			ring->pending = nil;
+			iunlock(ring);
+			dmaflush(0, ring->ctx, 8*4 << ctlr->csz);
+			qunlock(io);
+			nexterror();
+		}
+		if(io->b != nil){
+			freeb(io->b);
+			io->b = nil;
+		}
+		len = GET2(&p[6]);
+		dir = (p[0] & Rd2h) != 0;
+		if(len > 0){
+			io->b = allocb(len);		
+			if(dir == 0){	/* out */
+				assert(len >= n-8);
+				memmove(io->b->wp, p+8, n-8);
+			} else {
+				memset(io->b->wp, 0, len);
+				io->b->wp += len;
+			}
+		}
+		if((err = unstall(ep, ring)) != nil)
+			error(err);
+
+		if((ring->ctx[1]>>16) != ep->maxpkt){
+			u32int *w = slot->ibase;
+			w[0] = 0;
+			w[1] = 1<<ring->id;
+			w += (ring->id+1)*8<<ctlr->csz;
+			initepctx(w, ring, ep);
+			dmaflush(1, slot->ibase, 32*33 << ctlr->csz);
+			err = ctlrcmd(ctlr, CR_EVALCTX | (slot->id<<24), 0, PADDR(slot->ibase), nil);
+			dmaflush(0, slot->obase, 32*32 << ctlr->csz);
+			if(err != nil)
+				error(err);
+		}
+
+		queuetd(ring, TR_SETUPSTAGE | (len > 0 ? 2+dir : 0)<<16 | TR_IDT | TR_IOC, 8,
+			p[0] | p[1]<<8 | GET2(&p[2])<<16 |
+			(u64int)(GET2(&p[4]) | len<<16)<<32, &w[0]);
+		if(len > 0){
+			dmaflush(1, io->b->rp, len);
+			queuetd(ring, TR_DATASTAGE | dir<<16 | TR_IOC, len,
+				PADDR(io->b->rp), &w[1]);
+		}
+		queuetd(ring, TR_STATUSSTAGE | (len == 0 || !dir)<<16 | TR_IOC, 0, 0, &w[2]);
+
+		if((err = waittd(ctlr, &w[0], ep->tmout)) != nil)
+			error(err);
+		if(len > 0){
+			if((err = waittd(ctlr, &w[1], ep->tmout)) != nil)
+				error(err);
+			if(dir != 0){
+				dmaflush(0, io->b->rp, len);
+				io->b->wp -= (w[1].er[2] & 0xFFFFFF);
+				if(io->b->wp < io->b->rp)
+					io->b->wp = io->b->rp;
+			}
+		}
+		if((err = waittd(ctlr, &w[2], ep->tmout)) != nil)
+			error(err);
+
+		if(p[0] == 0x00 && p[1] == 0x09){
+			slot->confval = GET2(&p[2]);
+		} else if(p[0] == 0x01 && p[1] == 0x0d){
+			slot->altc = GET2(&p[2]);
+			slot->iface = GET2(&p[4]);
+		}
+
+		qunlock(io);
+		poperror();
+
+		return n;
+	} else if(ep->ttype == Tiso)
+		return isowrite(ep, p, n);
+
+	if((uintptr)p <= KZERO){
+		Block *b;
+
+		b = allocb(n);
+		if(waserror()){
+			freeb(b);
+			nexterror();
+		}
+		memmove(b->wp, p, n);
+		n = epwrite(ep, b->wp, n);
+		freeb(b);
+		poperror();
+		return n;
+	}
+
+	ctlr = (Ctlr*)ep->hp->aux;
+	io = (Epio*)ep->aux + OWRITE;
+	qlock(io);
+	if(waserror()){
+		dmaflush(0, io->ring->ctx, 8*4 << ctlr->csz);
+		qunlock(io);
+		nexterror();
+	}
+
+	if((err = unstall(ep, io->ring)) != nil)
+		error(err);
+
+	dmaflush(1, p, n);
+	queuetd(io->ring, TR_NORMAL | TR_IOC, n, PADDR(p), w);
+	if((err = waittd(ctlr, w, ep->tmout)) != nil)
+		error(err);
+
+	qunlock(io);
+	poperror();
+
+	return n;
+}
+
+static char*
+seprintep(char *s, char*, Ep*)
+{
+	return s;
+}
+
+static int
+portstatus(Hci *hp, int port)
+{
+	Ctlr *ctlr = hp->aux;
+	u32int psc, ps;
+
+	if(ctlr->port == nil || needrecover(ctlr))
+		return 0;
+
+	ps = 0;
+	psc = ctlr->port[port-1].reg[PORTSC];
+	if(psc & CCS)	ps |= HPpresent;
+	if(psc & PED)	ps |= HPenable;
+	if(psc & OCA)	ps |= HPovercurrent;
+	if(psc & PR)	ps |= HPreset;
+
+	if((hp->superspeed & (1<<(port-1))) != 0){
+		ps |= psc & (PLS|PP);
+		if(psc & CSC)	ps |= 1<<0+16;
+		if(psc & OCC)	ps |= 1<<3+16;
+		if(psc & PRC)	ps |= 1<<4+16;
+		if(psc & WRC)	ps |= 1<<5+16;
+		if(psc & PLC)	ps |= 1<<6+16;
+		if(psc & CEC)	ps |= 1<<7+16;
+	} else {
+		if((ps & HPreset) == 0){
+			switch((psc>>10)&15){
+			case 1:
+				/* full speed */
+				break;
+			case 2:
+				ps |= HPslow;
+				break;
+			case 3:
+				ps |= HPhigh;
+				break;
+			}
+		}
+		if(psc & PP)	ps |= HPpower;
+		if(psc & CSC)	ps |= HPstatuschg;
+		if(psc & PRC)	ps |= HPchange;
+	}
+
+	return ps;
+}
+	
+static int
+portenable(Hci*, int, int)
+{
+	return 0;
+}
+
+static int
+portreset(Hci *hp, int port, int on)
+{
+	Ctlr *ctlr = hp->aux;
+
+	if(ctlr->port == nil || needrecover(ctlr))
+		return 0;
+
+	if(on){
+		ctlr->port[port-1].reg[PORTSC] |= PR;
+		tsleep(&up->sleep, return0, nil, 200);
+	}
+	return 0;
+}
+
+static int
+reset(Hci *hp)
+{
+	static Ctlr ctlrs[2];
+	Ctlr *ctlr;
+	int i;
+
+	for(i=0; i<nelem(ctlrs); i++){
+		ctlr = &ctlrs[i];
+		if(ctlr->active == nil){
+			ctlr->active = hp;
+			ctlr->mmio = (u32int*)(VIRTIO + 0x8100000 + i*0x100000);
+			hp->aux = ctlr;
+			hp->port = (uintptr)ctlr->mmio - KZERO;
+			hp->tbdf = BUSUNKNOWN;
+			hp->irq = IRQusb1 + i;
+			goto Found;
+		}
+	}
+	return -1;
+
+Found:
+	hp->init = init;
+	hp->dump = dump;
+	hp->interrupt = interrupt;
+	hp->epopen = epopen;
+	hp->epclose = epclose;
+	hp->epread = epread;
+	hp->epwrite = epwrite;
+	hp->seprintep = seprintep;
+	hp->portenable = portenable;
+	hp->portreset = portreset;
+	hp->portstatus = portstatus;
+	hp->shutdown = shutdown;
+	hp->debug = setdebug;
+	hp->type = "xhci";
+
+	return 0;
+}
+
+void
+usbxhciimxlink(void)
+{
+	addhcitype("xhci", reset);
+}