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assemble:
BL receive_op
LDR R5, =0x20002000 // opcode table
LDR R1, =0x20001000 // opcode buffer base addr
loop:
LDR R0, [R5, 0] // load the string addr
BL string_compare
BEQ match
ADDS R5, 8 // next row of table
LDR R0, =0x20002080 // opcode table end
CMP R5, R0
BLO loop // Keep going if lower than end
B redo_line // redo line if opcode was not found
match:
LDR R6, [R5, 4] // load the parse instructions
main_loop:
MOVS R0, 0xFF // lsb mask
ANDS R0, R6 // store in R0
MOVS R1, 0x80 // bit 7 mask
TST R0, R1 // compare (AND) to R0 byte
BNE handle_imm // if IMM (== 1)
LSRS R0, 4 // R0 hold 3 or 4 (or 0)
BEQ handle_brackets // if BRACKETS (== 0)
handle_reg:
BL register // result is put in R4
MOVS R0, 0x0F // lower nibble mask
ANDS R0, R6 // store shift amount in R0
LSLS R4, R0 // shift the result by the shift amount
ORRS R5, R4 // OR the register code into the word under construction
B done_stuff
handle_imm:
MOVS R1, 0x0F // lower nibble mask
ANDS R0, R1 // store immediate width in R0
BL octal // result is put in R4
MOVS R0, 0x7F // least significant 7 bits mask
ANDS R0, R6 // store ls 7 bits in R0
LSRS R0, 4 // shift right to get shift amount
LSLS R4, R0 // shift the result by the shift amount
done_stuff:
LSRS R6, 0x8 // get next parse instruction
BEQ done // if it's zero there are no more things to parse
MOVS R0, 0 // copy the end_char into R0
ORRS R0, R9
BL uart_send // echo the comma (or bracket)
10:
BL get_char
MOVS R1, ' // space char
CMP R0, R1
BNE 10b // keep trying if not space
BL uart_send // echo the space
B main_loop
handle_brackets:
BL get_char // char in R0
MOVS R1, '[ // open bracket
CMP R0, R1
BNE handle_brackets // keep trying if not bracket
BL uart_send // echo bracket
MOVS R8, 1 // 1 means we are now in brackets
LSRS R6, 0x8 // get next parse instruction
BNE main_loop
done:
TST R8, R8 // R8 == whether we are in bracket or not
BEQ no_brackets
MOVS R0, '] // echo bracket
BL uart_send
no_bracket:
MOVS R0, '\r // send carriage return
BL uart_send
MOVS R0, '\n // send newline
BL uart_send
B next_instr
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