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176 missing description for mip csr #272

Merged
merged 8 commits into from
Nov 21, 2024
4 changes: 2 additions & 2 deletions arch/csr/mhartid.yaml
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ address: 0xf14
priv_mode: M
length: MXLEN
description: Reports the unique hart-specific ID in the system.
definedBy: I
definedBy: Sm
fields:
ID:
location_rv32: 31-0
Expand All @@ -17,4 +17,4 @@ fields:
description: hart-specific ID.
reset_value: UNDEFINED_LEGAL
sw_read(): |
return hartid();
return hartid();
144 changes: 3 additions & 141 deletions arch/csr/mie.yaml
Original file line number Diff line number Diff line change
Expand Up @@ -7,147 +7,9 @@ long_name: Machine Interrupt Enable
address: 0x304
priv_mode: M
length: MXLEN
definedBy: I
description: |
Per-type interrupt enables.
For a detailed description of interrupt handling, see <%= link_to(:section, 'sec:interrupts') %>.
The `mie` register is an
MXLEN-bit read/write register containing interrupt enable bits.
Interrupt cause number _i_ (as reported in CSR `mcause`) corresponds with
bit _i_ in
`mie`. Bits 15:0 are allocated to standard interrupt causes only, while
bits 16 and above are designated for platform use.
NOTE: Interrupts designated for platform use may be designated for custom use
at the platform's discretion.
An interrupt _i_ will trap to M-mode (causing the privilege mode to
change to M-mode) if all of the following are true:
* either the current privilege mode is M and the MIE bit in the
`mstatus` register is set, or the current privilege mode has less
privilege than M-mode;
* bit _i_ is set in both `mip` and `mie`;
* if register `mideleg` exists, bit _i_ is not set in `mideleg`.
These conditions for an interrupt trap to occur must be evaluated in a
bounded amount of time from when an interrupt becomes, or ceases to be,
pending in `mip`, and must also be evaluated immediately following the
execution of an __x__RET instruction or an explicit write to a CSR on
which these interrupt trap conditions expressly depend (including `mip`,
`mie`, `mstatus`, and `mideleg`).
Interrupts to M-mode take priority over any interrupts to lower
privilege modes.
A bit in `mie` must be writable if the corresponding interrupt can ever
become pending. Bits of `mie` that are not writable must be read-only
zero.
[NOTE]
====
The machine-level interrupt registers handle a few root interrupt
sources which are assigned a fixed service priority for simplicity,
while separate external interrupt controllers can implement a more
complex prioritization scheme over a much larger set of interrupts that
are then muxed into the machine-level interrupt sources.
'''
The non-maskable interrupt is not made visible via the `mip` register as
its presence is implicitly known when executing the NMI trap handler.
====
If supervisor mode is implemented, bits `mip`.SEIP and `mie`.SEIE are
the interrupt-pending and interrupt-enable bits for supervisor-level
external interrupts. SEIP is writable in `mip`, and may be written by
M-mode software to indicate to S-mode that an external interrupt is
pending. Additionally, the platform-level interrupt controller may
generate supervisor-level external interrupts. Supervisor-level external
interrupts are made pending based on the logical-OR of the
software-writable SEIP bit and the signal from the external interrupt
controller. When `mip` is read with a CSR instruction, the value of the
SEIP bit returned in the `rd` destination register is the logical-OR of
the software-writable bit and the interrupt signal from the interrupt
controller, but the signal from the interrupt controller is not used to
calculate the value written to SEIP. Only the software-writable SEIP bit
participates in the read-modify-write sequence of a CSRRS or CSRRC
instruction.
[NOTE]
====
For example, if we name the software-writable SEIP bit `B` and the
signal from the external interrupt controller `E`, then if
`csrrs t0, mip, t1` is executed, `t0[9]` is written with `B || E`, then
`B` is written with `B || t1[9]`. If `csrrw t0, mip, t1` is executed,
then `t0[9]` is written with `B || E`, and `B` is simply written with
`t1[9]`. In neither case does `B` depend upon `E`.
The SEIP field behavior is designed to allow a higher privilege layer to
mimic external interrupts cleanly, without losing any real external
interrupts. The behavior of the CSR instructions is slightly modified
from regular CSR accesses as a result.
====
If supervisor mode is implemented, bits `mip`.STIP and `mie`.STIE are
the interrupt-pending and interrupt-enable bits for supervisor-level
timer interrupts. STIP is writable in `mip`, and may be written by
M-mode software to deliver timer interrupts to S-mode.
If supervisor mode is implemented, bits `mip`.SSIP and `mie`.SSIE are
the interrupt-pending and interrupt-enable bits for supervisor-level
software interrupts. SSIP is writable in `mip` and may also be set to 1
by a platform-specific interrupt controller.
<%- if ext?(:Sscofpmf) -%>
Bits `mip`.LCOFIP and `mie`.LCOFIE
are the interrupt-pending and interrupt-enable bits for local counter-overflow
interrupts.
LCOFIP is read-write in `mip` and reflects the occurrence of a local
counter-overflow overflow interrupt request resulting from any of the
`mhpmevent__n__`.OF bits being set.
If the Sscofpmf extension is not implemented, `mip`.LCOFIP and `mie`.LCOFIE are
read-only zeros.
<%- end -%>
Multiple simultaneous interrupts destined for M-mode are handled in the
following decreasing priority order: MEI, MSI, MTI, SEI, SSI, STI, LCOFI.
[NOTE]
====
The machine-level interrupt fixed-priority ordering rules were developed
with the following rationale.
Interrupts for higher privilege modes must be serviced before interrupts
for lower privilege modes to support preemption.
The platform-specific machine-level interrupt sources in bits 16 and
above have platform-specific priority, but are typically chosen to have
the highest service priority to support very fast local vectored
interrupts.
External interrupts are handled before internal (timer/software)
interrupts as external interrupts are usually generated by devices that
might require low interrupt service times.
Software interrupts are handled before internal timer interrupts,
because internal timer interrupts are usually intended for time slicing,
where time precision is less important, whereas software interrupts are
used for inter-processor messaging. Software interrupts can be avoided
when high-precision timing is required, or high-precision timer
interrupts can be routed via a different interrupt path. Software
interrupts are located in the lowest four bits of `mip` as these are
often written by software, and this position allows the use of a single
CSR instruction with a five-bit immediate.
====
Restricted views of the `mip` and `mie` registers appear as the `sip`
and `sie` registers for supervisor level. If an interrupt is delegated
to S-mode by setting a bit in the `mideleg` register, it becomes visible
in the `sip` register and is maskable using the `sie` register.
Otherwise, the corresponding bits in `sip` and `sie` are read-only zero.
definedBy: Sm
description:
$copy: "mip.yaml#/description"
fields:
SSIE:
location: 1
Expand Down
150 changes: 148 additions & 2 deletions arch/csr/mip.yaml
Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,153 @@ name: mip
long_name: Machine Interrupt Pending
address: 0x344
priv_mode: M
description: Machine Interrupt Pending bits

# Description is shared with mie CSR (it copies it from here).
description: |
The `mie` and `mip` CSRs are MXLEN-bit read/write registers used when
the CLINT or PLIC interrupt controllers are present.
Note that the CLINT refers to an interrupt controller
used by some RISC-V implementations but isn't a ratified
RISC-V International standard.
The `mip` CSR contains information on pending interrupts, while `mie` is the corresponding
CSR containing interrupt enable bits.
Interrupt cause number _i_ (as reported in the `mcause` CSR)
corresponds to bit _i_ in both `mip` and `mie`.
Bits 15:0 are allocated to standard interrupt causes only, while
bits 16 and above are designated for platform use.
NOTE: Interrupts designated for platform use may be designated for custom use
at the platform's discretion.
An interrupt _i_ will trap to M-mode (causing the privilege mode to
change to M-mode) if all of the following are true:
* either the current privilege mode is M and the MIE bit in the `mstatus` register is
set, or the current privilege mode has less privilege than M-mode;
* bit _i_ is set in both `mip` and `mie`
* if register `mideleg` exists, bit _i_ is not set in `mideleg`.
These conditions for an interrupt trap to occur must be evaluated in a
bounded amount of time from when an interrupt becomes, or ceases to be,
pending in `mip`, and must also be evaluated immediately following the
execution of an __x__RET instruction or an explicit write to a CSR on
which these interrupt trap conditions expressly depend (including `mip`,
`mie`, `mstatus`, and `mideleg`).
Interrupts to M-mode take priority over any interrupts to lower
privilege modes.
Each individual bit in register `mip` may be writable or may be
read-only. When bit _i_ in `mip` is writable, a pending interrupt _i_
can be cleared by writing 0 to this bit. If interrupt _i_ can become
pending but bit _i_ in `mip` is read-only, the implementation must
provide some other mechanism for clearing the pending interrupt.
A bit in `mie` must be writable if the corresponding interrupt can ever
become pending. Bits of `mie` that are not writable must be read-only
zero.
[NOTE]
====
The machine-level interrupt registers handle a few root interrupt
sources which are assigned a fixed service priority for simplicity,
while separate external interrupt controllers can implement a more
complex prioritization scheme over a much larger set of interrupts that
are then muxed into the machine-level interrupt sources.
'''
The non-maskable interrupt is not made visible via the `mip` register as
its presence is implicitly known when executing the NMI trap handler.
====
If supervisor mode is implemented, bits `mip`.SEIP and `mie`.SEIE are
the interrupt-pending and interrupt-enable bits for supervisor-level
external interrupts. SEIP is writable in `mip`, and may be written by
M-mode software to indicate to S-mode that an external interrupt is
pending. Additionally, the platform-level interrupt controller may
generate supervisor-level external interrupts. Supervisor-level external
interrupts are made pending based on the logical-OR of the
software-writable SEIP bit and the signal from the external interrupt
controller. When `mip` is read with a CSR instruction, the value of the
SEIP bit returned in the `rd` destination register is the logical-OR of
the software-writable bit and the interrupt signal from the interrupt
controller, but the signal from the interrupt controller is not used to
calculate the value written to SEIP. Only the software-writable SEIP bit
participates in the read-modify-write sequence of a CSRRS or CSRRC
instruction.
[NOTE]
====
For example, if we name the software-writable SEIP bit `B` and the
signal from the external interrupt controller `E`, then if
`csrrs t0, mip, t1` is executed, `t0[9]` is written with `B || E`, then
`B` is written with `B || t1[9]`. If `csrrw t0, mip, t1` is executed,
then `t0[9]` is written with `B || E`, and `B` is simply written with
`t1[9]`. In neither case does `B` depend upon `E`.
The SEIP field behavior is designed to allow a higher privilege layer to
mimic external interrupts cleanly, without losing any real external
interrupts. The behavior of the CSR instructions is slightly modified
from regular CSR accesses as a result.
====
If supervisor mode is implemented, bits `mip`.STIP and `mie`.STIE are
the interrupt-pending and interrupt-enable bits for supervisor-level
timer interrupts. STIP is writable in `mip`, and may be written by
M-mode software to deliver timer interrupts to S-mode.
If supervisor mode is implemented, bits `mip`.SSIP and `mie`.SSIE are
the interrupt-pending and interrupt-enable bits for supervisor-level
software interrupts. SSIP is writable in `mip` and may also be set to 1
by a platform-specific interrupt controller.
<% if ext?(:Sscofpmf) -%>
bits `mip`.LCOFIP and `mie`.LCOFIE
are the interrupt-pending and interrupt-enable bits for local counter-overflow
interrupts.
LCOFIP is read-write in `mip` and reflects the occurrence of a local
counter-overflow overflow interrupt request resulting from any of the
`mhpmevent__n__`.OF bits being set.
<% end -%>
Multiple simultaneous interrupts destined for M-mode are handled in the
following decreasing priority order: MEI, MSI, MTI, SEI, SSI, STI, LCOFI.
[NOTE]
====
The machine-level interrupt fixed-priority ordering rules were developed
with the following rationale.
Interrupts for higher privilege modes must be serviced before interrupts
for lower privilege modes to support preemption.
The platform-specific machine-level interrupt sources in bits 16 and
above have platform-specific priority, but are typically chosen to have
the highest service priority to support very fast local vectored
interrupts.
External interrupts are handled before internal (timer/software)
interrupts as external interrupts are usually generated by devices that
might require low interrupt service times.
Software interrupts are handled before internal timer interrupts,
because internal timer interrupts are usually intended for time slicing,
where time precision is less important, whereas software interrupts are
used for inter-processor messaging. Software interrupts can be avoided
when high-precision timing is required, or high-precision timer
interrupts can be routed via a different interrupt path. Software
interrupts are located in the lowest four bits of `mip` as these are
often written by software, and this position allows the use of a single
CSR instruction with a five-bit immediate.
====
Restricted views of the `mip` and `mie` registers appear as the `sip`
and `sie` registers for supervisor level. If an interrupt is delegated
to S-mode by setting a bit in the `mideleg` register, it becomes visible
in the `sip` register and is maskable using the `sie` register.
Otherwise, the corresponding bits in `sip` and `sie` are read-only zero.
length: MXLEN
definedBy: Sm
fields:
Expand Down Expand Up @@ -256,4 +402,4 @@ fields:
<%- end -%>
type: RW-H
reset_value: 0
definedBy: Sscofpmf
definedBy: Sscofpmf
6 changes: 3 additions & 3 deletions backends/certificate_doc/templates/certificate.adoc.erb
Original file line number Diff line number Diff line change
Expand Up @@ -559,7 +559,7 @@ h| Privilege Mode | <%= csr.priv_mode %>
|===


==== <%= cert_model.name %> Format
==== Format
<% unless csr.dynamic_length?(arch_def) || csr.implemented_fields(arch_def).any? { |f| f.dynamic_location?(arch_def) } -%>
<%# CSR has a known static length, so there is only one format to display -%>
.<%= csr.name %> format
Expand Down Expand Up @@ -587,7 +587,7 @@ This CSR format changes dynamically with XLEN.

<% end # unless dynamic length -%>

==== <%= cert_model.name %> Field Summary
==== Field Summary

// use @ as a separator since IDL code can contain |
[%autowidth,separator=@,float="center",align="center",cols="^,<,<,<",options="header",role="stretch"]
Expand Down Expand Up @@ -627,7 +627,7 @@ a@
<%- end -%>
|===

==== <%= cert_model.name %> Fields
==== Fields

<%- if csr.implemented_fields(arch_def).empty? -%>
This CSR has no fields. However, it must still exist (not cause an `Illegal Instruction` trap) and always return zero on a read.
Expand Down
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