From 34aeefe35094442f8832842d704b09226c8a30f8 Mon Sep 17 00:00:00 2001
From: Daniel Jobson <jobson@tillitis.se>
Date: Thu, 7 Nov 2024 13:10:10 +0100
Subject: [PATCH] Add API for syscall
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Add a register to store an address to a syscall function defined in
firmware. Set the reset value to an illegal address, to make sure a call
to an unset address will halt the CPU.

Co-authored-by: Mikael Ågren <mikael@tillitis.se>
---
 hw/application_fpga/core/tk1/rtl/tk1.v | 24 ++++++++++++++++++++++++
 hw/application_fpga/fw/tk1_mem.h       |  1 +
 2 files changed, 25 insertions(+)

diff --git a/hw/application_fpga/core/tk1/rtl/tk1.v b/hw/application_fpga/core/tk1/rtl/tk1.v
index 4f481b5..80cfc17 100644
--- a/hw/application_fpga/core/tk1/rtl/tk1.v
+++ b/hw/application_fpga/core/tk1/rtl/tk1.v
@@ -78,6 +78,7 @@ module tk1 (
   localparam ADDR_APP_SIZE = 8'h0d;
 
   localparam ADDR_BLAKE2S = 8'h10;
+  localparam ADDR_SYSCALL = 8'h12;
 
   localparam ADDR_CDI_FIRST = 8'h20;
   localparam ADDR_CDI_LAST = 8'h27;
@@ -106,6 +107,10 @@ module tk1 (
   localparam FW_RAM_LAST = 32'hd00007ff;
 
 
+  // ILLEGAL_ADDR is outside of the physical memory, and will trap in
+  // the security monitor if accessed.
+  localparam ILLEGAL_ADDR = 32'h4f000000;
+
   //----------------------------------------------------------------
   // Registers including update variables and write enable.
   //----------------------------------------------------------------
@@ -134,6 +139,9 @@ module tk1 (
   reg  [31 : 0] blake2s_addr_reg;
   reg           blake2s_addr_we;
 
+  reg  [31 : 0] syscall_addr_reg;
+  reg           syscall_addr_we;
+
   reg  [23 : 0] cpu_trap_ctr_reg;
   reg  [23 : 0] cpu_trap_ctr_new;
   reg  [ 2 : 0] cpu_trap_led_reg;
@@ -257,6 +265,7 @@ module tk1 (
       app_start_reg     <= 32'h0;
       app_size_reg      <= 32'h0;
       blake2s_addr_reg  <= 32'h0;
+      syscall_addr_reg  <= ILLEGAL_ADDR;
       cdi_mem[0]        <= 32'h0;
       cdi_mem[1]        <= 32'h0;
       cdi_mem[2]        <= 32'h0;
@@ -315,6 +324,10 @@ module tk1 (
         blake2s_addr_reg <= write_data;
       end
 
+      if (syscall_addr_we) begin
+        syscall_addr_reg <= write_data;
+      end
+
       if (cdi_mem_we) begin
         cdi_mem[address[2 : 0]] <= write_data;
       end
@@ -421,6 +434,7 @@ module tk1 (
     app_start_we     = 1'h0;
     app_size_we      = 1'h0;
     blake2s_addr_we  = 1'h0;
+    syscall_addr_we  = 1'h0;
     cdi_mem_we       = 1'h0;
     ram_addr_rand_we = 1'h0;
     ram_data_rand_we = 1'h0;
@@ -476,6 +490,12 @@ module tk1 (
           end
         end
 
+        if (address == ADDR_SYSCALL) begin
+          if (!system_mode_reg) begin
+            syscall_addr_we = 1'h1;
+          end
+        end
+
         if ((address >= ADDR_CDI_FIRST) && (address <= ADDR_CDI_LAST)) begin
           if (!system_mode_reg) begin
             cdi_mem_we = 1'h1;
@@ -560,6 +580,10 @@ module tk1 (
           tmp_read_data = blake2s_addr_reg;
         end
 
+        if (address == ADDR_SYSCALL) begin
+          tmp_read_data = syscall_addr_reg;
+        end
+
         if ((address >= ADDR_CDI_FIRST) && (address <= ADDR_CDI_LAST)) begin
           tmp_read_data = cdi_mem[address[2 : 0]];
         end
diff --git a/hw/application_fpga/fw/tk1_mem.h b/hw/application_fpga/fw/tk1_mem.h
index 565d818..f88fae2 100644
--- a/hw/application_fpga/fw/tk1_mem.h
+++ b/hw/application_fpga/fw/tk1_mem.h
@@ -128,6 +128,7 @@
 #define TK1_MMIO_TK1_APP_SIZE 0xff000034
 
 #define TK1_MMIO_TK1_BLAKE2S 0xff000040
+#define TK1_MMIO_TK1_SYSCALL 0xff000048
 
 #define TK1_MMIO_TK1_CDI_FIRST 0xff000080
 #define TK1_MMIO_TK1_CDI_LAST 0xff00009c