94 lines
2.5 KiB
ArmAsm
94 lines
2.5 KiB
ArmAsm
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// file : uart.s
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// project : Löwe OS
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// authors : Elias Löwe <elias@lowenware.com>
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// address of UART for virt device in qemu
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// -----------------------------------------------------------------------------
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.global _uart_putc // print single character uart
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.global _uart_putx // print integer in HEX format to uart
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.global _uart_puts // print null-terminated string to uart
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// -----------------------------------------------------------------------------
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.text
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// helper to avoid extra data moving
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// @x1 character print
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uart_putc:
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STP x2, lr, [sp, -16]!
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MOV x2, 0x09000000 // set UART address
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STRB w1, [x2] // put character out
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LDP x2, lr, [sp], 16
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RET
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// -----------------------------------------------------------------------------
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// print character to uart
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// @x0 character print
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_uart_putc:
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STR lr, [sp, -16]!
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MOV x1, x0 // set arguments
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BL uart_putc // put character out
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LDR lr, [sp], 16
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RET
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// -----------------------------------------------------------------------------
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// @x0 integer to print
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_uart_putx:
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STP lr, x3, [sp, -32]!
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STP x0, x1, [sp, 16]
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LDR x3, =60 // init bits counter 64-4
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1:
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LSR x1, x0, x3 // shift to digit
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AND x1, x1, 0xF // keep only digit
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CMP x1, 9 // compare it to 9
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BLS 2f // less or equal
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ADD x1, x1, 0x37 // turn into ASCII HEX char
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B 3f // continue to output
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2:
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ADD x1, x1, 0x30 // turn into ASCII num char
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3:
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BL uart_putc // output carachter
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CBZ x3, 0f // if counter == 0 return
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SUB x3, x3, 4 // otherwise subtract counter by 4
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B 1b // repeat
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0:
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LDP lr, x3, [sp], 16
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LDP x0, x1, [sp], 16
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RET
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// -----------------------------------------------------------------------------
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// @x0 pointer to string
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_uart_puts:
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STR lr, [sp, -16]!
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STP x0, x1, [sp, -16]!
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1:
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LDRB w1, [x0], 1 // load byte of string from address in x0
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CBZ w1, 0f // return if zero
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BL uart_putc // put charcter out
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B 1b // loop
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0:
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LDP x0, x1, [sp], 16
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LDR lr, [sp], 16
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RET
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// -----------------------------------------------------------------------------
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