Add interrupt vector table description

Adds a tentative description of the interrupt vector table.
That has to be reviewed and adjusted.

Author: DanieleParravicini

doc/03_reference/exception_interrupts.rst

@@ -165,3 +165,82 @@ If a synchronous exception occurs whilst ``cpuctrl``.sync_exception_seen is set,
 
 When a double fault is detected, the ``double_fault_seen_o`` output is asserted for one cycle and ``cpuctrl``.double_fault_seen is set.
 Note that writing the ``cpuctrl``.double_fault_seen field has no effect on the ``double_fault_seen_o`` output.
+
+
+Interrupt vector table
+----------------------
+
+The interrupt vector table is located at ``mtvec``, and each entry can contain the code for 
+the interrupt/exception handling. The following table indicates the offset of the entry and 
+its description.
+
++-------------------------+------------------------------------------------------------+
+| offset in bytes         | Description                                                |
++=========================+============================================================+
+| 0x00                    | Boot                                                       |
++-------------------------+------------------------------------------------------------+
+| 0x04                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x08                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x0c                    | Machine software interrupt                                 |
++-------------------------+------------------------------------------------------------+
+| 0x10                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x14                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x18                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x1c                    | Machine timer interrupt                                    |
++-------------------------+------------------------------------------------------------+
+| 0x20                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x24                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x28                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x2c                    | Machine external interrupt                                 |
++-------------------------+------------------------------------------------------------+
+| 0x30                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x34                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x38                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x3c                    | reserved                                                   |
++-------------------------+------------------------------------------------------------+
+| 0x40                    | irq_fast_i[0]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x44                    | irq_fast_i[1]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x48                    | irq_fast_i[2]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x4c                    | irq_fast_i[3]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x50                    | irq_fast_i[4]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x54                    | irq_fast_i[5]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x58                    | irq_fast_i[6]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x5c                    | irq_fast_i[7]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x60                    | irq_fast_i[8]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x64                    | irq_fast_i[9]                                              |
++-------------------------+------------------------------------------------------------+
+| 0x68                    | irq_fast_i[10]                                             |
++-------------------------+------------------------------------------------------------+
+| 0x6c                    | irq_fast_i[11]                                             |
++-------------------------+------------------------------------------------------------+
+| 0x70                    | irq_fast_i[12]                                             |
++-------------------------+------------------------------------------------------------+
+| 0x74                    | irq_fast_i[13]                                             |
++-------------------------+------------------------------------------------------------+
+| 0x78                    | irq_fast_i[14]                                             |
++-------------------------+------------------------------------------------------------+
+| 0x7c                    | irq_fast_i[15]                                             |
++-------------------------+------------------------------------------------------------+
+| 0x80                    | irq_nm_i                                                   |
++-------------------------+------------------------------------------------------------+
+