Updated
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Dennis Gunia
286
OperatingSystem/monitor_v2/include/xmodem.s
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286
OperatingSystem/monitor_v2/include/xmodem.s
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;-------------------------------------------------------------------------
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; Z80 XMODEM implementation by Dennis Gunia
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; 2022 - www,dennisgunia.de
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;
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; important doc: https://web.mit.edu/6.115/www/amulet/xmodem.htm
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; http://www.blunk-electronic.de/train-z/pdf/xymodem.pdf
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;-------------------------------------------------------------------------
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;Symbols
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SYM_SOH equ 0x01
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SYM_EOT equ 0x04
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SYM_ACK equ 0x06
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SYM_NAK equ 0x15
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SYM_ETB equ 0x17
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SYM_CAN equ 0x18
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SYM_C equ 0x43
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;Memory locations
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MEM_VAR_BLOCK equ 0x40FB ;last block
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MEM_VAR_TIMEA equ 0x40FC ;timer var (mills)
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MEM_VAR_TIMER equ 0x40FE ;timer var (seconds)
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MEM_INT_VEC_T equ 0x40FE ;interrupt vector table
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MEM_LOC_LOAD equ 0x4400 ;load location for program
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;XMODEM routine
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xmodem_init:
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call A_RTS_OFF
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LD A,10100111b ; Init CTC Channel 3
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OUT (CS_CTC_2),A
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LD A,14 ; 1028.57Hz ISR
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OUT (CS_CTC_2),A
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LD A,00h ; Set CTC Ch3 Interrupt Vector
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OUT (CS_CTC_0),A
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;load int vector to ram
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ld hl,xmodem_int ;CTC Ch3 INT routine
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ld (0x4200 + 0x04),hl
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;reset timer vars
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ld hl,0x0000
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ld (MEM_VAR_TIMEA),hl
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ld (MEM_VAR_TIMER),hl
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ld a,0x42 ; Set interrupt vector register
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ld i,a
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im 2 ; Z80 Interrupt mode
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ld hl,MSG_START ; Print start banner
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call print_str
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ei ; Enable interrupts
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; init done. Continue with xmodem_await_conn
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call xmodem_wait
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xmodem_await_conn: ;Wait for initial connection
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ld a, SYM_C ;Send C to notify sender, that we want CRC
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call xmodem_out
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call xmodem_read_wait ;Read with timeout
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jp c, xmodem_await_conn ;Carry flag set = timeout -> repeat
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;else continue
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xmodem_packet: ;XmodemCRC packet start
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;use 1st byte to decide further processing
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cp SYM_EOT ;End of Transmission
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jp z, xmodem_packet_EOT
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cp SYM_CAN ;Cancel (Force receiver to start sending C's)
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jp z, xmodem_await_conn
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cp SYM_SOH ;Start of
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jp z, xmodem_packet_get
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jp xmodem_err ;anything else is an error -> abort transmission
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xmodem_packet_get: ;if first byte == SYM_SOH -> receive block
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call xmodem_read_wait ;get byte 2 => block ID
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jp c, xmodem_nak
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ld b,a
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ld (MEM_VAR_BLOCK), a ;store block id to memory
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call xmodem_read_wait ;get byte 3 => block ID complement
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jp c, xmodem_nak
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add b
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cp 255 ;both size infos should always sum to 255
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jp nz,xmodem_err ;if not 255 then its an error
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;calculate block start address in RAM
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;multiply by 128
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;use more efficient bit-wise operations
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dec a ;a-1 to remove 1 sector offset
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ld a,b
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rra ;shift 1 bit to the right
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and 0x7F
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ld h,a
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ld a,b
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dec a ;a-1 to remove 1 sector offset
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rrca ;shift bit0 to bit 7
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and 0x80 ;mask out all other bits
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ld l,a
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;result:
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;hl = 0aaaaaaa a000000
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ld de,MEM_LOC_LOAD
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add hl,de ;add calculated offset to base address
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;hl now contains the true start address of this sector
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ld b,128 ;preload counter for data baytes
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ld c,0 ;packet length counter ( used for overflow error )
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xmodem_packet_get_data: ;get 128 data bytes (loop)
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push hl ;push hl onto stack because xmodem_read_wait destroys hl
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call xmodem_read_wait ;read byte or timeout
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jp c, xmodem_nak ;if timeout -> nak and retry
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pop hl ;restore hl
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ld (hl), a ;store received byte in memory
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inc hl ;increment pointer
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inc c ;increment packet length counter
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dec b ;decerment data bytes remmaining
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jp nz, xmodem_packet_get_data ;if bytes remaining, loop
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;else continue with crc bytes
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xmodem_packet_get_crc: ;get 16-Bit CRC
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call xmodem_read_wait
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jp c, xmodem_nak
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ld d,a
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inc c
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call xmodem_read_wait
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jp c, xmodem_nak
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ld e,a
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inc c
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;de now contains CRC value
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;check if c is not bigger than 130 byte (128 data + 2crc)
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;TODO if so NACK
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;de contains 16-bit CRC
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;TODO if crc error NACK
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jp xmodem_ack ;ack block -> then jump to start again
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xmodem_packet_EOT: ;End of transmission SUB.
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ld a, SYM_ACK ;Acknowledge EOT
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call xmodem_out
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jp xmodem_end ;and end xmodem
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xmodem_err: ;non recoverable error -> abort
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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call xmodem_out
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ld a, SYM_CAN
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ld hl, MSG_ERROR
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call print_str
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;overflow to end
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xmodem_end:
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di ;disable interrupts
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call print_newLine ;print new line
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jp PROMPT_BEGIN ;return ti prompt
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;isr is used as counter for timeouts
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xmodem_int:
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di ;setup ISR (disable further interrupts, exchange registers)
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ex AF,AF'
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exx
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ld hl,(MEM_VAR_TIMEA) ;millis counter
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inc hl
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ld (MEM_VAR_TIMEA),hl
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ld de,1028 ;every 1028 millis counter
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sbc hl,de
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jp nz, xmodem_int_cont ;if less than 1028 millis, loop
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ld hl,0 ;reset millis
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ld (MEM_VAR_TIMEA),hl
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ld hl,(MEM_VAR_TIMER) ;incement seconds
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inc hl
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ld (MEM_VAR_TIMER),hl
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xmodem_int_cont: ;end isr
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ex AF,AF' ;restore registers
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exx
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EI ;enable interrupts
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reti ;exit ISR
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; A returns char
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; Carry is set if timeout
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xmodem_read_timeount equ 3 ;3 seconds timeout
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xmodem_read_wait:
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di
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ld hl,0
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ld (MEM_VAR_TIMEA),hl
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ld (MEM_VAR_TIMER),hl
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ei
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call A_RTS_ON
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xmodem_read_wait_loop:
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;check timeout
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ld hl,(MEM_VAR_TIMER)
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ld a, l
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cp xmodem_read_timeount
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jp z, xmodem_read_wait_timeout ;if timeout retry
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; if no timeout
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xor a ; a = 0
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out (CS_SIO_A_C), a ; select reg 0
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in a, (CS_SIO_A_C) ; read reg 0
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and 1 ; mask D0 (recieve char available)
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jp Z,xmodem_read_wait_loop ; wait if no char
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; if char avail
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in a, (CS_SIO_A_D) ; read char
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;call debug_a_hex
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push af
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call A_RTS_OFF
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pop af
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scf
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ccf
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ret ; return
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xmodem_read_wait_timeout:
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scf
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ret
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xmodem_out:
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out (CS_SIO_A_D), a
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call xmodem_wait_out
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ret
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xmodem_wait_out:
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sub a ;clear a, write into WR0: select RR0
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inc a ;select RR1
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out (CS_SIO_A_C),A
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in A,(CS_SIO_A_C) ;read RRx
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bit 0,A
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jr z,xmodem_wait_out
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ret
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MSG_ERROR:
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db "Error: unexpected byte",13,10,0
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MSG_START:
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db "Await xmodem connection",13,10,0
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xmodem_ack: ;ack routine. Only use when expecting transmission afterwards.
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ld a, SYM_ACK ;send ACK
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call xmodem_out
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call xmodem_read_wait ;wait for response
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jp c, xmodem_ack ;if timeout repeat
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jp xmodem_packet ;if received, continue with new packet
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xmodem_nak: ;nak routine. Only use when expecting transmission afterwards.
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ld a, SYM_NAK ;send NAK
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call xmodem_out
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call xmodem_read_wait ;wait for response
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jp c, xmodem_nak ;if timeout repeat
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jp xmodem_packet ;if received, continue with new packet
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xmodem_wait:
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ld hl, 0xFF
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ld bc, 0x01
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xmodem_wait_1:
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nop
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nop
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nop
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nop
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sbc hl,bc
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ret Z
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jr xmodem_wait_1
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