arch: arm: Set Zero Latency IRQ to priority level zero: #8109
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Are there any implications from SVC being blocked by zero-latency peripheral IRQs? I agree that Fault exceptions having highest priority (equal to zero-latency) is OK. |
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@ioannisg I can't think of any. You'd have to invoke an SVC in the zero latency peripheral IRQ to run into issues, which I don't see happening. And if the SVC is interrupted, it should still pick up where it left off without any issue. |
arch/arm/core/cortex_m/Kconfig
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| Zero-latency interrupt can be used to set up an interrupt at the | ||
| highest interrupt priority which will not be blocked by interrupt | ||
| locking. | ||
| Since Zero-latency ISRs will run in the same priority or possible at |
include/arch/arm/cortex_m/exc.h
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| #define _EXC_FAULT_PRIO 0 | ||
| #ifdef CONFIG_ZERO_LATENCY_IRQS | ||
| #define _EXC_ZERO_LATENCY_IRQS_PRIO 1 | ||
| #define _EXC_SVC_PRIO 1 |
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Thinking aloud, should SVC be masked? Why ZLI at same priority as SVC?
is the below correct?
#define _EXC_SVC_PRIO _EXCEPTION_RESERVED_PRIO
#ifdef CONFIG_ZERO_LATENCY_IRQS
#define _EXC_ZERO_LATENCY_IRQS_PRIO _EXC_SVC_PRIO
#define _IRQ_PRIO_OFFSET (_EXCEPTION_RESERVED_PRIO + 1)
#else
#define _IRQ_PRIO_OFFSET _EXCEPTION_RESERVED_PRIO
#endif
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I don't think SVCs should be masked, they weren't before, and shouldn't be now.
ZLI at the same priority as SVC, I messed up in the rebase here, it should be 0.
Set Zero Latency IRQ to priority level zero and SVCs to priority level one when Zero Latency IRQ is enabled. This makes Zero Zatency truly zero latency when the kernel has been configured with userspace enabled, or when IRQ offloading is used. Exceptions can still delay Zero Latency IRQ, but this is considered ok since exceptions indicate a serious error, and the system needs to recover. Fixes: zephyrproject-rtos#7869 Signed-off-by: Joakim Andersson <[email protected]>
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@cvinayak can you revisit? This looks good to me but I'd like someone else to take a look. |
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@agross-linaro @andrewboie @andyross Can you please take a look at this? |
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@andyross thank you |
Set Zero Latency IRQ to priority level zero and SVCs to priority level
one when Zero Latency IRQ is enabled.
This makes Zero Zatency truly zero latency when the kernel has been
configured with userspace enabled, or when IRQ offloading is used.
Exceptions can still delay Zero Latency IRQ, but this is considered
ok since exceptions indicate a serious error, and the system needs to
recover.
Fixes: #7869