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/* ################################################################################################# */
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/* ################################################################################################# */
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/* # << NEORV32 - crt0.S - Application Start-Up Code & Minimal Runtime Environment >> # */
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/* # << NEORV32 - crt0.S - Start-Up Code >> # */
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/* # ********************************************************************************************* # */
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/* # The start-up code provides a minimal runtime environment that catches all exceptions and # */
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/* # interrupts and delegates them to the handler functions (installed by user via dedicated # */
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/* # install function from the neorv32 runtime environment library). # */
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/* # ********************************************************************************************* # */
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/* # ********************************************************************************************* # */
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/* # BSD 3-Clause License # */
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/* # BSD 3-Clause License # */
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/* # # */
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/* # # */
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/* # Copyright (c) 2020, Stephan Nolting. All rights reserved. # */
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/* # Copyright (c) 2020, Stephan Nolting. All rights reserved. # */
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/* # # */
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/* # # */
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/* # ********************************************************************************************* # */
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/* # ********************************************************************************************* # */
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/* # The NEORV32 Processor - https://github.com/stnolting/neorv32 (c) Stephan Nolting # */
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/* # The NEORV32 Processor - https://github.com/stnolting/neorv32 (c) Stephan Nolting # */
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/* ################################################################################################# */
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/* ################################################################################################# */
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.file "crt0.S"
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.file "crt0.S"
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.section .text
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.section .text.boot
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.balign 4
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.balign 4
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.global _start
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.global _start
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// IO region
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// IO region
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.cfi_startproc
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.cfi_startproc
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.cfi_undefined ra
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.cfi_undefined ra
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// *********************************************************
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// *********************************************************
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// Clear register file
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// Clear register file
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// Assume 'worst case': rv32e
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// *********************************************************
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// *********************************************************
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__crt0_reg_file_clear:
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__crt0_reg_file_clear:
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//addi x0, x0, 0 // hardwired to zero
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//addi x0, x0, 0 // hardwired to zero
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addi x1, x0, 0
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addi x1, x0, 0
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addi x2, x0, 0
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addi x2, x0, 0
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Line 66... |
addi x8, x0, 0
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addi x8, x0, 0
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addi x9, x0, 0
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addi x9, x0, 0
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//addi x10, x0, 0
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//addi x10, x0, 0
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//addi x11, x0, 0
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//addi x11, x0, 0
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//addi x12, x0, 0
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//addi x12, x0, 0
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//addi x13, x0, 0
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addi x13, x0, 0
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//addi x14, x0, 0
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addi x14, x0, 0
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addi x15, x0, 0
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addi x15, x0, 0
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// since we dont know here if we are compiling for a rv32e architecture
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// we won't touch registers above x15
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// *********************************************************
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// TEST AREA / DANGER ZONE
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// *********************************************************
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__crt0_tests:
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nop
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// *********************************************************
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// *********************************************************
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// Setup stack pointer
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// Setup stack pointer
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// *********************************************************
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// *********************************************************
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__crt0_stack_pointer_init:
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__crt0_stack_pointer_init:
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Line 85... |
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// *********************************************************
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// *********************************************************
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// Setup global pointer
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// Setup global pointer
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// *********************************************************
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// *********************************************************
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#ifndef __BOOTLOADER_START_CODE__
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__crt0_global_pointer_init:
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__crt0_global_pointer_init:
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.option push
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.option push
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.option norelax
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.option norelax
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la gp, __global_pointer$
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la gp, __global_pointer$
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.option pop
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.option pop
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#endif
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// *********************************************************
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// *********************************************************
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// Init trap handler base address
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// Init trap handler base address
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// *********************************************************
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// *********************************************************
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Line 107... |
// *********************************************************
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// *********************************************************
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// Reset/deactivate IO/peripheral devices
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// Reset/deactivate IO/peripheral devices
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// Devices, that are not implemented, will cause a store access fault
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// Devices, that are not implemented, will cause a store access fault
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// which is captured but actually ignored due to the dummy handler.
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// which is captured but actually ignored due to the dummy handler.
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// *********************************************************
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// *********************************************************
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#ifndef __BOOTLOADER_START_CODE__
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__crt0_reset_io:
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__crt0_reset_io:
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li x11, IO_BEGIN // start of processor-internal IO region
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li x11, IO_BEGIN // start of processor-internal IO region
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__crt0_reset_io_loop:
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__crt0_reset_io_loop:
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sw zero, 0(x11)
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sw zero, 0(x11)
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addi x11, x11, 4
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addi x11, x11, 4
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bne zero, x11, __crt0_reset_io_loop
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bne zero, x11, __crt0_reset_io_loop
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#endif
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// *********************************************************
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// *********************************************************
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// Clear .bss section (byte-wise)
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// Clear .bss section (byte-wise)
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// *********************************************************
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// *********************************************************
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#ifndef __BOOTLOADER_START_CODE__
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__crt0_clear_bss:
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__crt0_clear_bss:
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la x11, __crt0_bss_start
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la x11, __crt0_bss_start
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la x12, __crt0_bss_end
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la x12, __crt0_bss_end
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__crt0_clear_bss_loop:
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__crt0_clear_bss_loop:
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Line 133... |
sb zero, 0(x11)
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sb zero, 0(x11)
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addi x11, x11, 1
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addi x11, x11, 1
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j __crt0_clear_bss_loop
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j __crt0_clear_bss_loop
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__crt0_clear_bss_loop_end:
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__crt0_clear_bss_loop_end:
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#endif
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// *********************************************************
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// *********************************************************
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// Copy initialized .data section from ROM to RAM (byte-wise)
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// Copy initialized .data section from ROM to RAM (byte-wise)
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// *********************************************************
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// *********************************************************
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#ifndef __BOOTLOADER_START_CODE__
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__crt0_copy_data:
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__crt0_copy_data:
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la x11, __crt0_copy_data_src_begin // start of data area (copy source)
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la x11, __crt0_copy_data_src_begin // start of data area (copy source)
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la x12, __crt0_copy_data_dst_begin // start of data area (copy destination)
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la x12, __crt0_copy_data_dst_begin // start of data area (copy destination)
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la x13, __crt0_copy_data_dst_end // last address of destination data area
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la x13, __crt0_copy_data_dst_end // last address of destination data area
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addi x11, x11, 1
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addi x11, x11, 1
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addi x12, x12, 1
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addi x12, x12, 1
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j __crt0_copy_data_loop
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j __crt0_copy_data_loop
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__crt0_copy_data_loop_end:
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__crt0_copy_data_loop_end:
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#endif
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// *********************************************************
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// *********************************************************
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// Call main function (with argc = argv = 0)
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// Call main function (with argc = argv = 0)
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// *********************************************************
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// *********************************************************
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// Go to endless sleep mode if main returns
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// Go to endless sleep mode if main returns
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// *********************************************************
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// *********************************************************
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__crt0_this_is_the_end:
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__crt0_this_is_the_end:
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csrrci zero, mstatus, 8 // mstatus: disable global IRQs (MIE)
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csrrci zero, mstatus, 8 // mstatus: disable global IRQs (MIE)
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wfi
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wfi
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__crt0_this_is_the_end_end:
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j . // in case WFI is not available
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j __crt0_this_is_the_end_end // in case Ziscr is not available
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// *********************************************************
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// *********************************************************
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// dummy trap handler (for exceptions & IRQs)
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// dummy trap handler (for exceptions & IRQs)
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// tries to move on to next instruction
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// tries to move on to next instruction
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Line 192... |
sw x9, 4(sp)
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sw x9, 4(sp)
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csrr x8, mcause
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csrr x8, mcause
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blt x8, zero, __crt0_dummy_trap_handler_irq // skip mepc modification if interrupt
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blt x8, zero, __crt0_dummy_trap_handler_irq // skip mepc modification if interrupt
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__crt0_dummy_trap_handler_compute_return:
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csrr x8, mepc
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csrr x8, mepc
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// is compressed instruction?
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// is compressed instruction?
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lh x9, 0(x8) // get compressed instruction or lower 16 bits of uncompressed instruction that caused exception
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lh x9, 0(x8) // get compressed instruction or lower 16 bits of uncompressed instruction that caused exception
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andi x9, x9, 3 // mask: isolate lowest 2 opcode bits (= 11 for uncompressed instructions)
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andi x9, x9, 3 // mask: isolate lowest 2 opcode bits (= 11 for uncompressed instructions)
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