935864ad9c
fix bug in RegFile input width, fix control logic bug with INC/DEC, change assembler output format, change programs to use d0 as space char value
65 lines
2.6 KiB
NASM
65 lines
2.6 KiB
NASM
// Program 1 register use map:
|
|
// r0 is the accumulator, r1 is often used to cache temp values
|
|
// r6 is LFSR tap pattern
|
|
// r7 is LFSR state value
|
|
// r8 is the preamble counter
|
|
// r9 is the total encryption length counter
|
|
// r11 is the read pointer
|
|
// r12 is the write pointer
|
|
init: LDI #d62
|
|
PUT r8
|
|
LDW r8
|
|
PUT r6 // tap will now be in r6
|
|
LDI #d63
|
|
PUT r8
|
|
LDW r8
|
|
PUT r7 // state will now be in r7
|
|
LDI #d0
|
|
PUT r11 // init read incrementer to 0
|
|
LDI #d64
|
|
PUT r12 // init write incrementer to 64
|
|
LDI #d61
|
|
PUT r8
|
|
LDW r8
|
|
PUT r8 // init r8 decrementer with number of preamble space chars
|
|
LDI #d64
|
|
PUT r9 // init r9 decrementer to total number of possible ciphertext chars
|
|
preamble_loop: LDI #d0 // get space character decimal 0
|
|
XOR r7 // bitwise XOR the current state with plaintext space to generate ciphertext
|
|
CLB r0 // clear the leading bit of the ciphertext as in requirements
|
|
STW r12 // store ciphertext to write pointer
|
|
LDI lfsr_routine // load address for the lfsr_routine label
|
|
JAL r0 // jump to the lfsr_routine label
|
|
NXT r12 // increment write pointer
|
|
NXT r9 // decrement number of remaining ciphertext characters
|
|
LDI main_loop // load the address of label main_loop
|
|
NXT r8 // decrement preamble counter
|
|
JEZ r0 // exit preamble loop if the preamble counter has just reached 0
|
|
LDI preamble_loop // load the address of label preamble_loop
|
|
JMP r0 // jump to preamble_loop if there are more space characters to encode
|
|
main_loop: LDW r11 // load the next plaintext byte
|
|
XOR r7 // bitwise XOR the current state with plaintext space to generate ciphertext
|
|
CLB r0 // clear the leading bit of the ciphertext as in requirements
|
|
STW r12 // store ciphertext to write pointer
|
|
LDI lfsr_routine // load address for the lfsr_routine label
|
|
JAL r0 // jump to the lfsr_routine label
|
|
NXT r11 // increment read pointer
|
|
NXT r12 // increment write pointer
|
|
LDI done // load address of label done
|
|
NXT r9 // decrement number of remaining ciphertext chars
|
|
JEZ r0 // jump to end of program if all ciphertext chars have been processed
|
|
LDI main_loop // load address of main_loop
|
|
JMP r0 // jump to main_loop if there is still space for message characters
|
|
lfsr_routine: GET r7 // get previous state
|
|
AND r6 // and state with taps to get feedback pattern
|
|
PTY r0 // get feedback parity bit
|
|
PUT r1 // store feedback bit to r1 temporarily
|
|
GET r7 // get previous state again
|
|
LSH #d1 // left shift previous state by 1
|
|
ORR r1 // or with parity bit to get next state
|
|
PUT r7 // put next state to r7
|
|
GET r14 // load link register
|
|
JMP r0 // return to function call address
|
|
done: DNE // flag the CPU as done
|
|
LDI #d255
|
|
JMP r0 |