def alloc_transfers():
global devh
global imgbuf
global irqbuf
global img_transfer
global irq_transfer
img_transfer = usb.alloc_transfer(0)
if not img_transfer:
return -errno.ENOMEM
irq_transfer = usb.alloc_transfer(0)
if not irq_transfer:
return -errno.ENOMEM
usb.fill_bulk_transfer(img_transfer, devh, EP_DATA, imgbuf,
ct.sizeof(imgbuf), cb_img, None, 0)
usb.fill_interrupt_transfer(irq_transfer, devh, EP_INTR, irqbuf,
ct.sizeof(irqbuf), cb_irq, None, 0)
return 0
def benchmark_in(ep):
global devh
global tv_start
global buf
if ep == EP_ISO_IN:
num_iso_pack = 16
else:
num_iso_pack = 0
xfr = usb.alloc_transfer(num_iso_pack)
if not xfr:
return -errno.ENOMEM
if ep == EP_ISO_IN:
usb.fill_iso_transfer(xfr, devh, ep, buf, ct.sizeof(buf),
num_iso_pack, cb_xfr, None, 0)
usb.set_iso_packet_lengths(xfr, ct.sizeof(buf) // num_iso_pack)
else:
usb.fill_bulk_transfer(xfr, devh, ep, buf, ct.sizeof(buf),
cb_xfr, None, 0)
tv_start = datetime.now()
# NOTE: To reach maximum possible performance the program must
# submit *multiple* transfers here, not just one.
#
# When only one transfer is submitted there is a gap in the bus
# schedule from when the transfer completes until a new transfer
# is submitted by the callback. This causes some jitter for
# isochronous transfers and loss of throughput for bulk transfers.
#
# This is avoided by queueing multiple transfers in advance, so
# that the host controller is always kept busy, and will schedule
# more transfers on the bus while the callback is running for
# transfers which have completed on the bus.
return usb.submit_transfer(xfr)