From 19d9faa568688604f14623987977e2c62d4fa8b0 Mon Sep 17 00:00:00 2001
From: Daniel Maslowski <info@orangecms.org>
Date: Mon, 16 Oct 2023 19:25:32 +0200
Subject: [PATCH] Add initial notes on trap handlers

Signed-off-by: Daniel Maslowski <info@orangecms.org>
---
 trap-handlers.adoc | 59 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 trap-handlers.adoc

diff --git a/trap-handlers.adoc b/trap-handlers.adoc
new file mode 100644
index 0000000..380752e
--- /dev/null
+++ b/trap-handlers.adoc
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+[[trap-handlers]]
+== Machine-Level Interrupts and Exceptions
+
+=== Delegation
+
+A RISC-V Machine mode execution environment may delegate handling interrupts and exceptions to the Supervisor or Hypervisor mode execution environment.
+
+For reference, see https://github.com/riscv/riscv-isa-manual/blob/main/src/machine.adoc#machine-cause-register-mcause[the definitions in the RISC-V ISA spec].
+
+==== Interrupts
+[%autowidth,float="center",align="center",cols=">,>,<",options="header",]
+|===
+| Code / Description |OpenSBI |oreboot SBI
+|0 _Reserved_ +
+1 Supervisor software interrupt +
+2 _Reserved_ +
+3 Machine software interrupt +
+4 _Reserved_ +
+5 Supervisor timer interrupt +
+6 _Reserved_ +
+7 Machine timer interrupt +
+8 _Reserved_ +
+9 Supervisor external interrupt +
+10 _Reserved_ +
+11 Machine external interrupt 
+12-15 _Reserved_ +
+&#8805;16 _Designated for platform use_ 
+| O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O
+| O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O +
+O
+
+X = explicitly set
+O = explicitly unset
+I = initial value unchanged
+
+==== Exceptions