[mask_rom] Initialize stack pointer later in startup code
Initializing the stack pointer as part of the C runtime section
of the start up code is more logical and helps align the code with
the spec.
Signed-off-by: Michael Munday <mike.munday@lowrisc.org>
diff --git a/sw/device/silicon_creator/mask_rom/mask_rom_start.S b/sw/device/silicon_creator/mask_rom/mask_rom_start.S
index f00ecd5..cdfd0f9 100644
--- a/sw/device/silicon_creator/mask_rom/mask_rom_start.S
+++ b/sw/device/silicon_creator/mask_rom/mask_rom_start.S
@@ -168,17 +168,6 @@
li a1, (1 << SRAM_CTRL_CTRL_RENEW_SCR_KEY_BIT) | (1 << SRAM_CTRL_CTRL_INIT_BIT)
sw a1, SRAM_CTRL_CTRL_REG_OFFSET(a0)
- // Set up the stack pointer.
- //
- // In RISC-V, the stack grows downwards, so we load the address of the highest
- // word in the stack into sp. We don't load in `_stack_end`, as that points
- // beyond the end of RAM, and we always want it to be valid to dereference
- // `sp`, and we need this to be 128-bit (16-byte) aligned to meet the psABI.
- //
- // If an exception fires, the handler is conventionaly only allowed to clobber
- // memory at addresses below `sp`.
- la sp, (_stack_end - 16)
-
/**
* Set well-defined interrupt/exception handlers
*
@@ -197,9 +186,9 @@
* State").
*/
- // Zero all writable registers except x2 (sp).
+ // Zero all writable registers.
li x1, 0x0
- // NOT x2 (sp) - We have already set it to the right value above.
+ li x2, 0x0
li x3, 0x0
li x4, 0x0
li x5, 0x0
@@ -251,7 +240,18 @@
.extern crt_section_clear
call crt_section_clear
- // Setup global pointer.
+ // Set up stack pointer.
+ //
+ // In RISC-V, the stack grows downwards, so we load the address of the highest
+ // word in the stack into sp. We don't load in `_stack_end`, as that points
+ // beyond the end of RAM, and we always want it to be valid to dereference
+ // `sp`, and we need this to be 128-bit (16-byte) aligned to meet the psABI.
+ //
+ // If an exception fires, the handler is conventionally only allowed to clobber
+ // memory at addresses below `sp`.
+ la sp, (_stack_end - 16)
+
+ // Set up global pointer.
//
// This requires that we disable linker relaxations, or it will be relaxed to
// `mv gp, gp`, so we disabled relaxations for all of `_mask_rom_start_boot`.
