USB_MEM_SMALL
if (size > USB_MEM_SMALL || align > USB_MEM_SMALL) {
err = usb_block_allocmem(tag, USB_MEM_BLOCK, USB_MEM_SMALL, &b,
f->offs = USB_MEM_SMALL * i;
f = &p->block->frags[p->offs / USB_MEM_SMALL];
#define USB_MEM_BLOCK (USB_MEM_SMALL * USB_MEM_CHUNKS)