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Clifford Wolf 2015-06-26 11:01:34 +02:00
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README.md
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@ -134,17 +134,23 @@ For the Dhrystone benchmark the average CPI is 4.167.
Custom Instructions for IRQ Handling
------------------------------------
The following custom instructions are supported when IRQs are enabled.
*Note: The IRQ handling features in PicoRV32 do not follow the RISC-V
Privileged ISA specification. Instead a small set of very simple custom
instructions is used to implement IRQ handling with minimal hardware
overhead.*
The following custom instructions are only supported when IRQs are enabled
via the `ENABLE_IRQ` parameter (see above).
The PicoRV32 core has a built-in interrupt controller with 32 interrupts. An
interrupt can be triggered by asserting the corresponding bit in the `irq`
input of the core.
When the interrupt handler is started, the `eoi` End Of Interrupt (EOI) signals
for the handled interrupts goes high. The `eoi` signal goes low again when the
for the handled interrupts go high. The `eoi` signals go low again when the
interrupt handler returns.
The IRQs 0-2 can be triggered internally and have the following meaning:
The IRQs 0-2 can be triggered internally by the following built-in interrupt sources:
| IRQ | Interrupt Source |
| ---:| -----------------------------------|
@ -155,7 +161,7 @@ The IRQs 0-2 can be triggered internally and have the following meaning:
The core has 4 additional 32-bit registers `q0 .. q3` that are used for IRQ
handling. When an IRQ triggers, the register `q0` contains the return address
and `q1` contains a bitmask of all active IRQs. This means one call to the interrupt
handler might need to service one than more IRQ when more than one bit is set
handler might need to service more than one IRQ when more than one bit is set
in `q1`.
Registers `q2` and `q3` are uninitialized and can be used as temporary storage