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Harald Welte laforge at gnumonks.orgHi Peter and others, On Sat, Feb 18, 2012 at 08:18:33PM +0100, Peter Stuge wrote: > I note that all data to be transmitted is copied byte for byte from > the rctx data buffer into the USB peripheral memory. I had expected > zero copy. During copying, interrupts are disabled. I'm actually not sure on the latter part: * the hardware and IRQ handler code supports nested interrupts * the core IRQ handler assembly code re-enables interrupts immediately even before calling the USB driver * the endpoint re-fill code called from the irq handler __udp_refill_ep() doesn't contain any explicit local_irq_disable() * the USART interrupt priority (4) is higher than the USB prio (2) So based on all this, the USART interrupt should happily be served as a nested IRQ even while the USB driver is re-filling the end-point FIFO. Regards, Harald -- - Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)