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61 lines
3.3 KiB
ArmAsm
61 lines
3.3 KiB
ArmAsm
/* -----------------------------------------------------------------------------
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* Project Name : Architectures of Processor Systems (APS) lab work
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* Organization : National Research University of Electronic Technology (MIET)
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* Department : Institute of Microdevices and Control Systems
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* Author(s) : Andrei Solodovnikov
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* Email(s) : hepoh@org.miet.ru
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See https://github.com/MPSU/APS/blob/master/LICENSE file for licensing details.
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* ------------------------------------------------------------------------------
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*/
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_start:
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# Initialize register values
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0: 050000b7 li x1, 0x05000000 # save UART RX base address
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4: 02000137 li x2, 0x02000000 # save LED controller base address
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8: 0001c1b7 li x3, 0x0001c200 # set baud rate to 115200
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c: 20018193
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10: 0030a623 sw x3, 0x0c(x1)
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14: 00100213 li x4, 0x00000001 # set parity bit
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18: 0040a823 sw x4, 0x10(x1)
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1c: 000011b7 li x3, 0x00000D0D # save special code for blink mode
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20: d0d18193
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24: 00008237 li x4, 0x00000808 # save special code for reset
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28: f7f20213
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2c: 0ff00493 li x9, 0x000000ff # save mask for clearing the upper bytes
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30: 00100313 li x6, 0x00000001 # save one
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34: 04c00293 la x5, trap_handler # the la pseudo-instruction loads a number similarly to li,
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38: 00028293 # but in the case of la the number is the address
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# of the specified location (the trap handler address);
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# this pseudo-instruction will be split into two
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# instructions: lui and addi
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3c: 30529073 csrw mtvec, x5 # set the interrupt vector
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40: 000102b7 li x5 , 0x00010000 # prepare the interrupt mask for the single
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# (zeroth) input
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44: 30429073 csrw mie, x5 # load the mask into the mask register
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# Call main function
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main:
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48: 00000063 beq x0, x0, main # infinite loop, equivalent to while (1);
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# TRAP HANDLER
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# Without external intervention the processor will never reach the instructions below;
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# however, upon an interrupt the program counter will be loaded with the address of
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# the first instruction below.
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# Save used registers to the stack
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trap_handler:
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4c: 0000a383 lw x7, 0(x1) # load value from UART RX
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50: 00947433 and x8, x8, x9 # clear the upper 3 bytes
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54: 00841413 slli x8, x8, 8 # shift register x8 left by 1 byte
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58: 00746433 or x8, x8, x7 # write the byte read from RX into the vacated position
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5c: 00340863 beq x8, x3, blink_mode # if blink special code received, jump to blink_mode
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60: 00440a63 beq x8, x4, reset # if reset special code received, jump to reset
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64: 00812023 sw x8, 0(x2) # write the value to LEDs
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68: 30200073 mret # return control to the program (pc = mepc),
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# which means returning to the infinite loop
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blink_mode:
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6c: 00612223 sw x6, 4(x2) # write 1 to led_mode
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70: 30200073 mret
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reset:
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74: 02612223 sw x6, 0x24(x2) # write 1 to led_reset
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78: 30200073 mret
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