diff --git a/firmware/ice40-riscv/icE1usb/usb_desc_app.c b/firmware/ice40-riscv/icE1usb/usb_desc_app.c
index ec01854..663be0b 100644
--- a/firmware/ice40-riscv/icE1usb/usb_desc_app.c
+++ b/firmware/ice40-riscv/icE1usb/usb_desc_app.c
@@ -90,7 +90,7 @@
 				.bEndpointAddress	= USB_EP_E1_INT(0),
 				.bmAttributes		= 0x03,
 				.wMaxPacketSize		= 10,
-				.bInterval		= 3,
+				.bInterval		= 4,	/* every 4 ms */
 			},
 		},
 		.on = {
@@ -110,7 +110,7 @@
 				.bDescriptorType	= USB_DT_EP,
 				.bEndpointAddress	= USB_EP_E1_IN(0),
 				.bmAttributes		= 0x05,
-				.wMaxPacketSize		= 388,
+				.wMaxPacketSize		= 292,
 				.bInterval		= 1,
 			},
 			.ep_data_out = {
@@ -118,7 +118,7 @@
 				.bDescriptorType	= USB_DT_EP,
 				.bEndpointAddress	= USB_EP_E1_OUT(0),
 				.bmAttributes		= 0x05,
-				.wMaxPacketSize		= 388,
+				.wMaxPacketSize		= 292,
 				.bInterval		= 1,
 			},
 			.ep_fb = {
@@ -126,8 +126,8 @@
 				.bDescriptorType	= USB_DT_EP,
 				.bEndpointAddress	= USB_EP_E1_FB(0),
 				.bmAttributes		= 0x11,
-				.wMaxPacketSize		= 8,
-				.bInterval		= 3,
+				.wMaxPacketSize		= 3,
+				.bInterval		= 3,	/* every 2^(3-1) = 4 ms */
 			},
 			.ep_interrupt = {
 				.bLength		= sizeof(struct usb_ep_desc),
@@ -135,7 +135,7 @@
 				.bEndpointAddress	= USB_EP_E1_INT(0),
 				.bmAttributes		= 0x03,
 				.wMaxPacketSize		= 10,
-				.bInterval		= 3,
+				.bInterval		= 4,	/* every 4 ms */
 			},
 		},
 	},
diff --git a/firmware/ice40-riscv/icE1usb/usb_e1.c b/firmware/ice40-riscv/icE1usb/usb_e1.c
index 8e78ffa..75811c2 100644
--- a/firmware/ice40-riscv/icE1usb/usb_e1.c
+++ b/firmware/ice40-riscv/icE1usb/usb_e1.c
@@ -128,10 +128,8 @@
 		/* Get some data from E1 */
 		int n = e1_rx_level(0);
 
-		if (n > 64)
-			n = 12;
-		else if (n > 32)
-			n = 10;
+		if (n > 32)
+			n = 9;
 		else if (n > 8)
 			n = 8;
 		else if (!n)
@@ -177,7 +175,7 @@
 
 refill:
 		/* Refill it */
-		ep_regs->bd[bdi].csr = USB_BD_STATE_RDY_DATA | USB_BD_LEN(388);
+		ep_regs->bd[bdi].csr = USB_BD_STATE_RDY_DATA | USB_BD_LEN(292);
 
 		/* Next BDI */
 		bdi ^= 1;
@@ -282,8 +280,8 @@
 
 		/* EP OUT: Queue two buffers */
 		ep_regs = _get_ep_regs(USB_EP_E1_FB(0));
-		ep_regs->bd[0].csr = USB_BD_STATE_RDY_DATA | USB_BD_LEN(388);
-		ep_regs->bd[1].csr = USB_BD_STATE_RDY_DATA | USB_BD_LEN(388);
+		ep_regs->bd[0].csr = USB_BD_STATE_RDY_DATA | USB_BD_LEN(292);
+		ep_regs->bd[1].csr = USB_BD_STATE_RDY_DATA | USB_BD_LEN(292);
 
 		/* EP Feedback: Pre-fill */
 		_usb_fill_feedback_ep();