170 lines
3.7 KiB
Plaintext
170 lines
3.7 KiB
Plaintext
// Serial port address in MMIO
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dw UART: 0x40000
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// Reserve space for our read buffer
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resb SERIAL_BUFFER: 1024
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dw SER_READ_PTR: 0
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dw SER_WRITE_PTR: 0
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serial_init: func
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lwi SERIAL_BUFFER, rg0
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stw rg0, SER_READ_PTR, 0
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stw rg0, SER_WRITE_PTR, 0
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return
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serial_isr:
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push rg0
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push rg1
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push rg2
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ldw UART, rg0
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ldb rg0, rg1, 2 // load ser_in_valid flag
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// no serial input
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jez rg1, _serial_isr_end
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// we should have a valid byte to read at offset 3
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ldb rg0, rg1, 3 // data byte
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// write data to ptr and increment
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ldw SER_WRITE_PTR, rg2
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stb rg1, rg2
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addi rg2, 1
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// load buff+1024
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lwi SERIAL_BUFFER, rg0
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addi rg0, 1024, rg1
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// if ptr != buff+1024, nowrap.
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ine rg1, rg2, rg1
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jnz rg1, _serial_isr_nowrap
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lwi SERIAL_BUFFER, rg2 // set the pointer
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_serial_isr_nowrap:
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stw rg2, SER_WRITE_PTR
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_serial_isr_end:
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pop rg0
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pop rg1
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pop rg2
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iret
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// read_byte: emulator → kernel
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// reads data from base+0x00, valid flag at base+0x01
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read_byte: func
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push rg0
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push rg1
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push rg2
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ldw UART, rg1
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_serial_read_wait:
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ldb rg1, rg0, 2 // base+0x02 = read valid flag
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lli 0x01, rg2
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ieq rg0, rg2, rg2
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jnz rg2, _serial_read_ready
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hlt
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jmp _serial_read_wait
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_serial_read_ready:
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ldb rg1, rg0, 3 // base+0x03 = data byte
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stb zero, rg1, 2 // clear read valid flag
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stb rg0, bpr, 8 // return byte
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pop rg2
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pop rg1
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pop rg0
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return
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// _serial_send: kernel → emulator
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// writes data to base+0x01, valid flag to base+0x00
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_serial_send:
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push rg0
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push rg2
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push rg3
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push rg4
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push rg5
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ldw UART, rg5
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_serial_wait:
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ldb rg5, rg2, 0 // base+0x00 = ser_out_valid
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lli 0x01, rg3
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ieq rg2, rg3, rg4
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jnz rg4, _serial_wait // wait while emulator hasn't consumed yet
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stb rg0, rg5, 1 // base+0x01 = ser_out_data
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lli 0x01, rg2
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stb rg2, rg5, 0 // base+0x00 = ser_out_valid = 1
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pop rg5
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pop rg4
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pop rg3
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pop rg2
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pop rg0
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ret
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// ------------------------------------------
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// prints the null-terminated string at addr(arg[0])
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print: func
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push rg0
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push rg1
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push rg2
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ldw bpr, rg0, 8 // load string address from arg
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_serial_print_loop:
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ldb rg0, rg1 // load byte
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ieq rg1, zero, rg2 // null terminator?
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jnz rg2, _serial_print_end
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push rg0 // save string pointer
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mov rg1, rg0
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call _serial_send
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pop rg0
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addi rg0, 1, rg0
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jmp _serial_print_loop
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_serial_print_end:
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pop rg2
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pop rg1
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pop rg0
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jmp _serial_end
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// ------------------------------------------
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// prints the last byte of arg[0]
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print_byte: func
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push rg0
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ldw bpr, rg0, 8
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call _serial_send
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pop rg0
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jmp _serial_end
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// ------------------------------------------
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_serial_end:
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return
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// ------------------------------------------
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// reads up to rg1 bytes into buffer at rg2
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// args: buf_size @ bpr+8, buf_addr @ bpr+12
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// returns: 0 in bpr+8 on success, 1 on nullptr error
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buf_read: func
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push rg0
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push rg1
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push rg2
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push rg3
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ldw bpr, rg1, 8 // buf size
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ldw bpr, rg2, 12 // buf addr
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jez rg2, _buf_read_err // return err if nullptr
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_buf_read_loop:
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jez rg1, _buf_read_end
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call read_byte
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ldw bpr, rg3, 8 // read return value from frame
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stb rg3, rg2 // store into buffer
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addi rg2, 1, rg2
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subi rg1, 1, rg1
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jmp _buf_read_loop
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_buf_read_end:
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stw zero, bpr, 8 // return 0 (success)
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pop rg3
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pop rg2
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pop rg1
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pop rg0
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return
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_buf_read_err:
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lli 1, rg0
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stw rg0, bpr, 8 // return 1 (error)
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pop rg3
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pop rg2
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pop rg1
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pop rg0
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return
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