diff -r 578be2adaf3e -r 307f4279f433 Adaptation/GUID-F09740DA-015B-449D-A124-0BEABBDDCB52.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Adaptation/GUID-F09740DA-015B-449D-A124-0BEABBDDCB52.dita Fri Oct 15 14:32:18 2010 +0100 @@ -0,0 +1,78 @@ + + + + + +Enabling +and DisablingThis document describes how device drivers enable and disable interrupts. +

Drivers can enable and disable the interrupts on the relevant interrupt +sources while handling the interrupts using the Interrupt class. +Typically, handling an interrupt is done with disabled interrupts. The interrupt +is then enabled after the completion of interrupt handling.

+Interrupt::Disable(aIntId); +... +// handle interrupt +... +Interrupt::Enable(aIntId); + +/** + Interrupt Service Routine (ISR) for the UART driver. This function + is associated with the UART interrupt, EUartIrq (value obtained from + TRM). This function is called whenever there is an interrupt on this + interrupt line and the interrupt source is enabled. The ISR must be a + static void function, taking a single TAny* parameter, which is an + object passed at the time of binding, usually a pointer to the owning + class. Interrupt::Enable() must be called to start receiving + interrupts. + + The ISR implementation is hardware and driver specific. The ISR must + be self-contained as the state of the system is indeterminate. It + should not signal threads, allocate or de-allocate memory, copy + memory to or from user processes, or call most Kernel functions. + Also the whole system is blocked while the ISR is running, so it must be + kept as short as possible. Any lengthy processing must be done in a + delayed function call (DFC). + + A typical ISR would, + Clear the interrupt in the peripheral. + Disable the interrupt. + Read or write peripheral registers, e.g. to determine errors, or + to start a new task. + Read data from, or write data to, the peripheral. + Start or stop NTimers or DMA transfer operations. + Queue DFCs. + + @param aParam + pointer to object passed as parameter while binding + */ + +void DExUartPhysicalChannelH4::UartIsr(TAny* aParam) + { + // Do the high priority device specific interrupt handling + // i.e. read the interrupt type from device, clear the + // interrupt. + ... + // Defer the remaining processing by queuing the respective + // DFC based on the interrupt type + ... + } +

Some operations may need to be performed with all the interrupts, not just +the particular interrupt source, disabled. In this case, the NKern class +must be used to disable and enable all interrupts globally at the Interrupt +controller. NKern::DisableAllInterrupts() can disable all +IRQs, or IRQs and FIQs. NKern::RestoreInterrupts() can +restore the interrupts to their state before disabling.

+alevel = 1; // 1 to disable IRQs and 2 to disable IRQs and FIQs +state = NKern::DisableAllInterrupts(aLevel); +... +// perform the required operations +... +NKern::RestoreInterrupts(state); + + \ No newline at end of file