95 lines
1.6 KiB
ArmAsm
95 lines
1.6 KiB
ArmAsm
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/*
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* Copyright (c) 2024, Barcelona Supercomputing Center (BSC)
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* SPDX-License-Identifier: MIT
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*
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* RBOOTROM v1.0
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* Modified by Rodrigo Arias Mallo <rodrigo.arias@bsc.es>
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*
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* This is a custom bootrom that prints some information to the UART when
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* starting, as well as when it hangs. It assumes the UART is at UART_BASE and
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* it will jump to DRAM_BASE to continue the boot.
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*/
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#define DRAM_BASE 0x80000000
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#define UART_BASE 0x40001000
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.macro PUTC, ch
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li a0, \ch
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jal putchar
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.endm
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.section .text.start, "ax", @progbits
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.globl _start
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_start:
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jal print_hello // Print initial message on HART 0 only
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csrr a0, mhartid // Load HART ID into a0
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li s0, DRAM_BASE // Load next address into s0
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jr s0 // Jump to s0
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.section .text.hang, "ax", @progbits
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.globl _hang
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_hang:
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PUTC '\n'
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PUTC '\r'
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PUTC 'R'
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PUTC 'B'
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PUTC 'O'
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PUTC 'O'
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PUTC 'T'
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PUTC 'R'
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PUTC 'O'
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PUTC 'M'
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PUTC ' '
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PUTC 'H'
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PUTC 'A'
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PUTC 'N'
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PUTC 'G'
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PUTC '\n'
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PUTC '\r'
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/* Hang */
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csrr a0, mhartid
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1:
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wfi
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j 1b
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.section .text, "ax", @progbits
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putchar:
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// Wait a bit before writing to UART
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li t0, 100000 // Delay a bit
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1:
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addi t0, t0, -1 // Decrement
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bne t0, zero, 1b // Repeat if not zero
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// Write the character now
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la t0, UART_BASE // Transmitter Holding Buffer
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sb a0, 0(t0) // Write a0 byte
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ret
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print_hello:
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csrr t0, mhartid // Load HART ID into a0
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beq t0, zero, 1f // Print message on HART 0 only
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ret
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1:
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// Identify bootroom
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PUTC '\n'
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PUTC '\r'
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PUTC 'R'
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PUTC 'B'
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PUTC 'O'
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PUTC 'O'
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PUTC 'T'
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PUTC 'R'
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PUTC 'O'
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PUTC 'M'
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PUTC ' '
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PUTC 'v'
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PUTC '1'
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PUTC '.'
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PUTC '0'
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PUTC '\n'
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PUTC '\r'
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ret
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