MIPS Interface: Difference between revisions

{{#invoke:Register table|head|700px|MI_BB_SECURE_EXCEPTION <code>0x0430 0014</code>}}

| U-? || U-? || U-? || U-? || U-? || U-? || W-? || W-?

| — || — || — || — || — || — || — || SK RAM Access

| U-? || U-? || U-? || U-? || U-? || U-? || U-? || U-?

| RW-0 || RW-0 || RW-0 || RW-0 || RW-0 || RW-0 || RW-1 || RW-1

| Module || Button || MI error || PI error || Timer || Application || Boot memory swap || Secure mode

| 25 | Unknown | System software writes to this bit when launching an app or game. (TODO determine the purpose of this bit)

| 24 | SK RAM Access | Setting this bit to 1 enables access to an 0x8000-byte SRAM mapped at 0x1FC40000 outside of secure mode.

| 7 | Module | Secure trap caused by the memory card being removed. (TOVERIFY)

| 6 | Button | Secure trap caused by the power button being pressed. (TOVERIFY there should be some way to control whether this event causes a secure trap or an Int2/PreNMI interrupt)

| 5 | MI error | Secure trap caused by an MI error.

| 4 | PI error | Secure trap caused by a PI error.

| 3 | Timer | Secure trap caused by the secure timer.

| 2 | Application | Secure trap caused by an application reading this register outside of secure mode.

| 1 | Boot memory swap | If this is set to 1 the boot ROM is mapped to 0x1FC00000 and Secure Kernel RAM is mapped at 0x1FC20000; this is the state at cold boot. If this is not set the Secure Kernel RAM is mapped at 0x1FC00000 and the boot ROM is mapped at 0x1FC20000.

| 0 | Secure mode | Secure Kernel writes 0 here to exit secure mode. This is effective immediately, all future memory accesses that miss the CPU cache will be unable to access secure mode resources. Whenever this register is written to without the intention to exit secure mode, a 1 must be re-written here.

: Secure traps are implemented as an NMI to the CPU and are vectored to 0xBFC00000, this register is then used by the Secure Kernel as a Cause register to determine the reason for the secure trap and the relevant handler is entered.

: Reading (and possibly writing, TOVERIFY) this register from non-secure mode (i.e. from a game or application) causes a secure trap with the Application bit set in this register. This mechanism is how SKCs (Secure Kernel calls) are implemented; the application sets up the required CPU registers for the call before reading this register to trigger the Application trap.