From 3522b3d0cdd47520eaf45187c6d1851dc15ff53b Mon Sep 17 00:00:00 2001
From: Alek Ratzloff <alekratz@gmail.com>
Date: Mon, 9 Mar 2020 18:42:31 -0400
Subject: [PATCH] Update spec and register offset for interrupts

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>
---
 src/libvm/src/state.rs |  9 +++++++--
 vm.md                  | 10 +++++-----
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/libvm/src/state.rs b/src/libvm/src/state.rs
index 8f11818..c2cd5e0 100644
--- a/src/libvm/src/state.rs
+++ b/src/libvm/src/state.rs
@@ -169,6 +169,10 @@ impl State {
         Ok(slice)
     }
 
+    // stack size of 288 - yowza
+    // Maybe we don't need 32 registers... this works out to 288
+    const INTERRUPT_REG_SPACE: u64 = (R31 - R00 + 4) as u64 * 8;
+
     /// Invoke an interrupt.
     pub fn interrupt(&mut self, return_ip: u64, index: usize, aux: u64) -> Result<u64> {
         assert!(index < IVT_LENGTH, "invalid interrupt index");
@@ -192,8 +196,9 @@ impl State {
             self.push(Source::Reg(reg))?;
         }
 
+
         let sp = self.sp();
-        self.set_reg_unchecked(FP, sp - 48);
+        self.set_reg_unchecked(FP, sp - Self::INTERRUPT_REG_SPACE);
         self.set_reg_unchecked(R00, index as u64);
         self.set_reg_unchecked(R01, aux);
 
@@ -203,7 +208,7 @@ impl State {
     /// Exit/return from the current interrupt.
     pub fn exit_interrupt(&mut self) -> Result<u64> {
         let fp = self.fp();
-        let sp = fp + 48;
+        let sp = fp + Self::INTERRUPT_REG_SPACE;
 
         self.set_reg_unchecked(SP, sp);
 
diff --git a/vm.md b/vm.md
index 50f5477..c1aa0fd 100644
--- a/vm.md
+++ b/vm.md
@@ -228,16 +228,15 @@ wrapping around to 0.
         * Push the IP of the next instruction to be called
         * Push the FLAGS register
         * Push the STATUS register
-        * Push the R0 register
-        * Push the R1 register
+        * Push the R0-R31 registers
         * Update the IP (i.e., jump) to the address of the given interrupt vector in the IVT
         * Update the R0 register to the value in the first parameter
         * Update the R1 register to the value in the second parameter
-        * Update the frame pointer to the current stack pointer - 48
+        * Update the frame pointer to the current stack pointer - 288
 * IRet
     * Opcode: 0x3005
     * When this instruction is executed, these actions occur:
-        * Update the stack pointer to the current frame pointer + 48
+        * Update the stack pointer to the current frame pointer + 288
         * Pop the old R1 value
         * Pop the old R0 value
         * Pop the old STATUS value
@@ -410,8 +409,9 @@ A VM must provide support for the following meta-values:
 
 # General TODO
 
+* Memory permissions
 * MMIO regions
-* Paging?
+* Paging
 * Determine how address sizes are determined
     * source size <= dest size - zero extend source and copy
         * mov %r0, (label)u32