The following two sections of code are 'specials' for the 512. In both cases the code was actually saved in a live machine and disassembled, so as to ensure complete accuracy and to permit mernory addresses to be included in the listings, as both sections of code are position dependent. (i.e. slightly dirty and self modifying). DisassembIy was also used for two other reasons. First for 6502.SYS it was done to produce a source listing which looks more like a normal assembly code program to 6502 users, necessitated by the reason given below. The OSWORD &FA code was disassembled from a live system for the simple reason that neither source code nor source documentation was available in any form other than the input parameter spedfications detailed in chapter 6. The strange techniques employed in this code are due to two factors. The first is that Acorn commonly used relative addressing so as to make the code relocatable as far as possible, eg:
*0 clear A
BEQ so-where Branch sc-where - always
The second is that all Acorn 6502 code appears to be produced using MASM, which simply does not produce the same effidency as hand written assembly code.
The first listing is of the tube handling code which resides in the 6502.SYS file on the DOS boot disc. Interestingly, the original source was actually written in DOS and assembled using a cross-assembler the source for which looks slightly strange if you are not familiar with 8086 assembler.
The reason a DOS cross-assembler was used was that it appears from other information we cannot publish that the source code was at one time intended to be easily modifiable for use by other hardware than a BBC rnicro and a 512!!
The first section of code is the program from 6502.SYS proper, while following it there is the patch which resides at &2300 to handle the OSWORD &FA, which was originally also in 6502.SYS. OSWORD &FA was removed from disc for practical reasons as well as 'neatness'.
The code was separated so it could be put into the 512's boot ROMS to enable it to assist virtually irrunediately with the rapid tube transfers used on initial system start-up, rather than itself first having to be '*LOAD'ed from an ADFS disk, which would look untidy and of course would take longer.
6502.SYS provides the main support for cross-tube dialogue between the 512 and the host for the majority of 512 operations. Only when a tube claim or release is called for, or a completely standard MOS or filing system function is required, is the tube host code, resident in pages 4 to 6 of the host called.
TUBE handling code for the Master $12
This code uploads to the 512 during initial system boot.
The boot strap loader looks for a file 6502.SYS in the root directory of the DOS+ boot disk and uploads it to the 512's MX alonq with DOS+.
Before initialisinq the system it
downloads this code to 6502 memory at offset £2800.
It then sets the naer vector to point to the code's first
executable instruction at £2803
To make the code accessible to the boot-strap loader:
NOTE - that scras of the code here is position critical and much of it is also time critical. Various addresses and data declarations for the 6502 MOS calls and hardware interfaces follow.
ZERO PAGE VARIABLES
ken - &EC new ks~ press in zero page
- 'ED old key press in zero ~aqe STANDARD MOS CALLS & VECTORS USED BY THIS CODE
keyvec - &22B The keyboard vector oswrch - aFFEE Console (screen) ontput osbfte - &FFF4 General MOS call entry
ADDRESS OF ZnttflcSPTEfl BRC MICRO VECTORS userv - ~2OO user vector brkv - &202 The break vector irqvl - &204 Interrupt requeSt 1 eventvec - &220 The event vector
ENTRY TO BBC n:cao~s STAhrDUO ~UBE CODE tube_entry - &40~ c1aAjn~re1ease/pro4raTh tube n"I
SHeILA K-fly MAPPED ADDRESSES ic~ge - &rsoo ban, addrena of SHEILA erte_addr - &FE00 eels CRTC address register crtc_data - &FE01 'e45 CRTC data register unerport - &FEEC user-port data I-a up_rdwrt - &FEE2 User-port data direction AcRu - &Ftea 6522 auxiliary control register Ihtu - &FEED Iaterruflt flag register IrRn - &FEGD Interrupt flag register IERU - &FESE Interrupt enable register
1770 FDC OFFSETS FROM &FEOO Master fdc base - &24 Master_fdn_stat - &28 Master_fdc_data - &2B BBC_fdc_base - &80 BBC_fdc_stat - &84 BBC_fda_data - &e7
THE TUBE STATUS AND DATA REGISTERS ********************************** tubeaistat - &ttto Register 1 status tubenidata - ~FEE1 Register 1 data tube~stat - &FEE2 Register 2 status tubefldata - &FEE3 Register 1 data tuben3stat - aFERA Register 3 statue tubefladata - Register S data tubsR4stat - aFEES Register 4 status tubeR4data - &FU7 Register A data
OSWOSD TYPE DEC~TIoNs GRAPH_OSWOafl - fast graphics update nrsK_oswonn - STE hard disk read~write (unirr.lemented) RESERVED - &FD was tert OSWORD CRTC OSSIORD - SFC curmor, soft scroll, mouse etc FDC_OSSORD - iFfl seek/read/write RESEflVZfl - bik xfer onward
FILING SYSTEM Co~*4ANDs
usfind - &FFCE o~nIclose file
osgbpb - &FFfl1 read~vrite open file
filefdc_atri - 0 select drivt/flt-flhl~.
fdc_atat - 4 nRC, INDEX,RMV,~C, - fda_=td - 4 REsTORS~sEEKIRtAn/WRrTE fdc_trek - S 0-79 fda sect - 6 1-10 tdc_data - 7 data for PEAfl/watT~, track for SEEK
"MI DECLARATIONS nnd code &OnOO MM! handler location - FIXEnt =r_stat - &0D02 direction patch location nrni rd - &ODOB direction patch location wr aODOE direction ~atch location
NMI ZERO PAGE WORKSPACE nmiwso &A0 temporary status storage nadwal - &A1 end of ccrmnand semaphore nmiwsfl &AS nmiws3 &AS nmiws4 - &A4 nTniws5 = &A5 nrniwsS &Ae nn!ws7 &A7 ;Aliases fdc bans - nmiwso indirect all accesses to FDC fdo base 10 - nmiwso fdc base_hi - nmiwsl
BEGINNING Cr 512 TUBE COOS 2100 JMP &2500 not one of the following so j~ to OSWOTID ~FA code 2e0a atp .0-il_OSSORD graphics update? 2005 REQ &262B ~--4 to_gra~h_'trite 2107 CbtP &~cRTC_OSWORD cursor OSSORD? Zecs %zQ ~2O26 beq to_nuword_fe 260B CMP &~DIs~_oswonn hard disk OSWOflfl? 280D BEC $2825 b&~q to_oaword_fe 2B0r CMP *TDc_osWOstn floppy disk contro~lnr OSNORD? 2B11 EEC &le2E beq to_onvord_fda 2613 JkP &2600 else default code
n-ny RESERVED FOR TRANSIENT STORAGE Temporary storage for FDC operations 2S16 cpa_dras EQUD C 281A tam_statu. EQUB 0 211Th &~rw aid ~fl C 2S1e .s,ctor_count 501,3 0 2am error_-sir EQUB 0 2S1E ran_c-rd EQUB 0 261r &~vatchdogl EQUB 0 2020 -watchdogz scum 0
screen address mn~d mouse pointer co-ordinates 2S21 &~moua.jr~hi tat's 0 2022 &~mau5e~~lo taun 0 2S23 mouse_x_hi ECUB 0 2S24 won,._x_10 SOUTh 0
The following code overcomes the liatted brancbin4 range of conditional it-s from the initial entry by converting them to direct unconditional jumps to OSWORD fe
2B25 JMP &2c2r J~ to CO-On RTS to osgord tc 2S2e JMP ~2A7F write 6B~5 data - atip onword_fc to_graph_write 2B2a JMP ~29r8 Graphics output - 5~ graph_write to osuord fdc 282t axp &28E0 Floppy disk - j~ caword_fdc -newevont ~sS1 aMp &2Arc J~ to event handler - eventeode .n~w_irq 2834 JMP &2ne0 J~ to nouirql
**ttt~ The main operational mutinca now follow
get one byte fr~ register 2 .getflldata 2837 LDA tubeUZatat Teat bit 7 of n 5tatus 2S3A BPL &2940 Not set - branch to tu$~_oavrch 2B3C LDA tube~data Read fl data 20SF a's -tube oswrch 2640 LDA tubeRlatat Test bit 7 of Ri statu5 2eI~ SPL get~oata J~ to getfl if set 2S4S LDA tubeRidata Read Ri data 2646 JSR os'&~rch write character 264n JMP tube_osvrch Repeat; write on. byte to register 2 write fl 284e SIT tubePUstat Test bit 6 of fl stat 2851 avc write_~ Not set - loop until it is! 2853 STA tnbe~data write 't2 data 2856 RTS Get one byte fr~ register C read RI 2057 BIT tubeRcatat Teat bit 7 of Re stat 2e5A BPL read_Ra Not 5et - loop nntil it is! 2S5c LDA tubencoata asad R4 data 2asF RTS write one byte to register 4 'trite RI 2S60 BIT tubea4stat test bit ~ of R4 stat 2e63 BVC write_Rd Not set - 1o~ until it is! 2S~5 STA tuben4data write RI data 29~ a's write one byte to register I write al 2069 BIT tubenistat Teat bit 6 or Ri stat 286C BVC write_Ri Not set - loop until it i5'&~ 2S6t STA tubenidata write RA data 2671 RTS
Foe OSSORD for "1)1770 5 1~4" r's'~ floppy controller the floppy controller uses five registers
0 special control latch 4 ca-and/status 5 track register 6 sector register 7 data register &~'' wArtNIN~! - POSITION DEPENDENT CODE FOL~S
.fdc exec 2B72 InA *0 2S7~ S~A i2a1A sta ram_etatus ensure clear initially 2e77 WY *7 idy &~fdc_data - ensure drq not pending 2879 LDA C&AO},Y ida (ido_base ,y 2R75 JSR ~et&2data 287t STA &2a1n eta error_mask - save tar dSsk mt. 2981 JSR qet~data 2864 StA &2e1c sta sector_count - multi sector count 20S7 Jsrt getfldata jar getnidata - read coinmand from 1R6 289A STA &281E sta rain_cmr'd - for multi sector xfer 296D JSR &2072 jsr tube~rograrn - set dm addr in 186 zego LDY 44 lay &~fdc_mand 2092 rflA &291E ida ram 2895 STA (&AO).Y ata (fac_base},y - send cur-and to f& 2897 mm *&co I. it group S~4 2899 CMP *&CO were top two bits set 7 209e BNE &26cE bne fdc_e7 - No! leava to interrupt . 289n InA &~&3C 2S~r STA &2SiF sta watebdogi 28fl InA 40 2BA4 STA &2620 sta watchdoq2 20k? TAX Set up tic-out Counter5 2SAS WY *4 idy *fdc_stat - point to atatus reg -fdc el 2SAA flEx 2SAn BNE s2SAA Loop fdc_ci until status goam busy .fdc e2 2SAn LDA $1 I Te5t busy flaq 2SAr AND t'AO~~Y ANn (fac_base~,y in the status register
~INC! - the foliowina insttuction must not lie on an a&Irtas where the bottom 3 bits are set zael nno s28c5 Branch fdc_e4 If no longer busy 2Bn3 DEC &2820 dec watchdog2 29B6 BNE &2SAA bne fda_el
28RS nEC &2e1F dec watchdogl
2mB mit aQOXA bne fdc_ci - else tall thru on timeout
20nn Ink faFF and return a timeout error
28SF BWE &zecs bne fdc_es (will always branch)
-fdc e4 28C1 WY *4 Arty itdc_stat - get the status 2SCS LOA c&AO) ,Y ida (fdc_base ry .fdc es 2Bc5 STA &281A Save status for return in ram_status .fdc_eS 2Bc6 SET Disable interrupts 2Sc9 asa 'nAEF generate mc event to return status 2S00 CLI Enable inter~pta 28CD RTS and return .tdc e7 2Sct BPL &2SDF bpl fdc_e9 - ctp 1 co-wade return now 2Sn0 u)y *0 Others don't, no load ti'tSout counters 2sn2 Wx *0 fda as 28n4 LDA ~~9t6 ida status~nding and check Fnc atatna 28fl7 ENS &2scs bne fdc_e6 - it finished return status 2Sn9 flEx Ir not finished decrement counter 28DA mm &29D4 Not done, btanch fdc_en - wait a while 28nc oty 28nn BrIE &2eD4 bne fdc_es it still not co-lete. else .fdc eg 2Sflr RTS Timer event returns status
mc OSWORD proper
&~OSWORD fdc 28E0 CLI , Enable interrupts again 28E1 cw Ensure operation in binary 29E2 asa qetfldata Read tube RZ data - get a cormnd 28E5 WrE aQete , It > 0 jnp to tube call 1 - else- - - fdc OSWORD ret 28g7 RTS , Done!
I The5e routines claim or release the tube, set up the l'70 addresses for the host taacbine, or write data to nemory mapped 1-0 In SHEILA.
tube call 1 29E6 CKP &~i Master 128 co~nd? 2eEA BITE &28F3 No! - Try tube_call_2 CB/B+ Qote jsrt tube_setup Get tube params - store at rw_cmd &281B 2OEr JSR move_NM:_data Copy and adapt nmi routine 26r2 Jsn &293A jar Master_setup - set up regs 26r5 Jsn &2872 jsr fdc_exec - qet and execute connand 2SFe JMP &26E0 OMP csword_tdc - get another byte tube call 2
2er9 t *2 aec ~'~+' coninand?
nero ant tube_call_3 no! - Try tube_call_3
28FF JSR tube_setup Get tube params - store at rw_cmd a2a1n 2~O2 Jsn move_NMI data copy and adapt the nm* routine 2905 Jsn &2932 jar nBc_setup - set up reqa for BBC 290S JSR &2972 jsr fdc_exec get and e~ecute command 290s JMP &28E0 imp OSWORD_fda get another byte tube call S
a(p *3 Claim tube required? 2910 BNE tnbe_call 4 No! try tube_call_4
2912 asa &2983 jar anti_claim - qet control of rynit 2915 JSK &2956 Get tube - ist tube_claim 2918 J,(p &26E0 JKp osuord_fac - get another byte tube call_4 2919 CMP #4 Release tubs? 2910 nt;E &2926 No! branch other_out~ut 291r JSR &2s7n jsr tube_release - give up tube 2922 JSk &2990 Call fluff_release give up NMI 2925 Jxp &26E0 JMP onward_fdc - qet another byte
.other_output 2929 TAX port n-er in x 2929 JaR qet~data Read tube ~ data - get data byte 292c STA &FEOO,X atore in 4o~age, X - write it to ~rt 292F Jnp 62BEQ 3Wp onward_fdc - qet anothet byte
.SW_setup 2932 'Dx &~&e4 Sec_f& stat 2g34 Kny &~&87 sBc_fdc_data 2~36 Lok IaSO nnc_fdc_bane 293S -E '2940 bne Setupi - always flaster_setup 293A LOX &~&26 Manter_fdc_stat 293c Lay &~~2n Master_fdc_data 2~3R LDA &~&24 Master_fdc_base setupt 2940 STA &Ao sta fdc_base_lo - patch for indirection 2942 LDA farE Load in~age (Sheila) high byte 2944 STA ski sta fdc_base_hi 2946 S7X &n02 str rflfti_stat - Patch nini status read 2e49 JSR geta2data Are we perfcrminq write? 2g4c EKO &2952 zero is No! go to setup2 for read 294E STY aDot sty nifli wr - patch the rual write code 2951 RTS setup2 2952 STY aDDS sty stat_rd - patch the nrni read code 2955 RTS
.tube_claim 2956 InA #&Cl A 1~3 to claim tube 2~5S Jsft tube_entry Call tube data transfer at &4O~ 295R flea tube claim If c-C tailed, repeat until success 295n RTS
.tube_setup 295E LCX SD Fill in dma address
.fdc amal ~96O csn getn2data Read tube R2data - get 1 Cf 4 bytes 2~6a STA &2816,x Store it in epra_dina,x 2966 IflX 2967 crx *4 Done 4 times? 2969 Sflt &2960 No! - Repeat fac dinal 2968 JSR getn2data Read tube n2da~a get nw coffrnand 296s STA &2a1B Store tube n2data at rw-Crnd 2971 RTS
.tubejrcqram 2972 tflA &2s1n A - stored rw cmd - dna claimer type 2975 IsX *&16 sot X to cflra_dma low byte 2977 WY t&29 Set Y to cpm_dran high byte 29?9 asa tube_entry call tube data transfer at &406 297c RTS -tube release 297D LDA &~&ei A - 129 to release tube 297r JSR tube_entry call tube code at &406 - release tube 2982 RTS
These routines claim or release NMI ownership according to whether tube data transfer is to take place or disc access is required. In practical terms only one of three facilities can be the current NMI owner, the disc system, the network handler (econet), or the tube. A copy of this routine's NMI code is kept at nmi_image (29DB) and transferred to page &D when NMI ownership is required. The routines are called by the code in tube_call_1 to tube_call_4.
.nu~i claim 2993 LLA iSAF Set n~ paged ROM service request 29e5 LnX *&C for N"r clajaL 2987 WY ISFF 2~s9 JSR oubyte Claim NMI routine 29S0 STY s299A Store oriqinal IlMI RON No- at nmi owner 29SF RTS risi release 2990 ~r &299A Load Y with original ami_owner 299a LDA &~~8r set up Paged Row serviec re~est 2995 tox &~as for NMI release 299~ JKP osbyte Release NMI to previous owner owner 299A ~Un 0 move N'S' data ~)( Move 32 bytes of NMI data to page 6D
.rmd nut 2990 IDA &29na.x ida n~i_irftaqe,x - (saved orig IlMI data) 29A0 STA &0DOO,x ata rud_code.x (Restore to NMI paqe &0 2~A3 flEx Completed 32 tim..? 29A4 SPL &299D No! - repeat tram nini_nut 29A6 ft~s -nmi next sect 29A7 WY 94 idy tfdc_stat - status req offset 29A9 Lox (iAo~~Y ida (fac_base),y - qet the status 29as STA &281A sta ram_status - save for return status 291& AND &281D and error_mask - any error bits on? 29n1 nNt &29n5 bne ntai next exit - Yes' - abort it 29B3 LDA ~2BlE Ida ram_cmnd-test for groupi (seek ea 29e6 Ert &29D5 bpl arni_next_exit - Yes! Then finished 2~SS u)A &2810 ida sector_count -get remaining sectors ~~SS CMF 41 c~ *1 - is it the last one? 29BD BEQ a2SDS beq nri_next_exit - signal final mt 29nr DEC &261c * dec sectot connt - count down sectors 29c2 WY 56 ldy &~tdc_sect 29c4 LDA (~AO),Y ida cfdc_base~,y - get the sector req 29c6 CLO Clear carry tlaq 29C7 AbC *1 Move to next sector 2909 STA (&AO~.Y sta (tdc_base~,y - and insert new value 29GB LDA &2S1E ida ram_0=4 get read~write 29CE AND &~&F3 Remove head settle delay 29D0 WY &~4 Idy &~tdc_crand 29n2 STA (&AO},Y sta (fdc_base),y - fire off again 29D4 RTS .nni next exit 29D5 LDA &~SFF Flag an FDC event ~9D7 STA &29F6 Set status~nding to return statu5 2~nA RTS
-flrai_image aBNE pni save context onoo 29nc LDA SEECO 6945 address register ODOl 29Dr Ann Get error bits 0n04 29E1 CKp &~3 + Busy ~ ODOS 2StS mm ~2SED Final interrupt - nimi_exit ODOR 29E5 LDA tuben3data tither this or the next inn ODOA 2~tS StA tabertadata patcb.d to paint to FDC ODin fl9En puk Restore context 0Db 29Ec RTI Return from interrupt onli nad_exit 29~ TYA 01)12 aSEK Pr" Save Y onla 29Er JSR &29A7 Next sector or finish 0014 2S72 PEA Restore context 0017 29F3 TAY Restore y ODiS 2SFA era Restore a 001~ Z9r5 RTI Return fr~ interrupt OnlA status~ndinq 29r~ EQUB C onin - return 29F7 RTS Return from OSWORD
Copy bit patterns to 6502 for block write & ~raphics
This part of the code fills 6502 screen RAM with bit patterns sent across by the 186. This can either be font bytes in a1~ha ~de or virtual graphics screen bytes in graphics mOde Operations are: a) send screen address MSB - or zero to sto~ b) send screen address LSB c) send S font bytes, Ct 1 byte for background~space fill d) send sync byte - or iFF to repeat from a) a wait for sync response f) increment pointer, qo to C -graph_write 2SFS eLr Enable interrupts QSFS cLD Ensure we operate in binary next addr hi 29rA JSR qet~data nead fl for hi-byte until data received 29FD SEQ &29F7 no data? - finished - go to RTS 29FF S~A ~71 Store n content. at zero page &71 next addr 10 2AO~ LDA tube~stat Read '12 status until ready 2A04 BPL &2301 Not ready? - repeat, branch next addr 10 2A06 LDA tube~data Read 't2 for 10-byte 2A09 TAr and keep in Y 2A0A LDA *0 Clear low byte 230c STA &?O Zero ~7O (real low byte is in Y)
Writing to the screen is optimised for maxirnum possible speed, hence these routines are written 'longhand and so avoid the use of counters, instructions to decrement them and the tests to check when the loop is complete. Spaces are further optimised because they are the most frequently written character and only need a sinqle fill byte. They are therefore the easiest to write too as no reading of tubendata is required between bytes. transfer_loop1 writes spaces, transfer_loop2 other bytes.
transfer_loop1 2AOE LDA tubenstat Read n2 status - wait for vayne byte 2A11 BPL &2AOE Repeat until S bytes ready in ni buffer 2A13 LDA tuben2data Read R2 data-remove sync byte~cbeck chr 2A16 SEQ s2A43 If 0 qo to transfer_1c0p2 - qet S bytes 2A1B OMP *&F~ ~ither a space or the end of output 2A1A EEC &29FA aFF-end. branch next_addr_hi to repeat 2A1C LDA tubeRidata Read al data for sflace fill pattern 2AiF STA (&70} ,Y * and move same byte into main screen RAM 2~~1 INY S times an fast an ponsible 2fl2 STA (&70}.Y 2A21 INY 2~~5 STA (s7O ,Y 2A27 INY 2A28 STA C&70 ,Y 2A2A INY 2112 STA (&70),Y 2fl9 INY 2A2E STA (670 ,Y 2A30 rNY SASi STA (&70 r ZAS3 INY 2A34 STA (&70) Y SA~6 INY 2A37 BNE &2AOt wait for sync unless on page boundary 2A39 rNC &71 Increment hiqh byte first 2A3n flPL &2AOE check for wrap around - bpl transter_loopt 2A3n LDA t'40 40 back to bottom of screen 2A3F STA '71 by resetting hi byte 2A41 SME a2A0E cuickest j~ to transfer_loopi transfer_loop2 2A43 LDA tubauldata Read Ri data - 1st byte - 7 left 2A4~ STA c&703 ,Y ZACS INY 2A49 LDA tubeuldata Read at data - 2nd byte - 6 left 2A4c STA (&10) ,y 2A4t INY 234r LDA tubeRld&ta Road RI data - 3rd byte - 5 lett 2An2 STA (~7O~.Y 2AS4 PHY 2MS InA tubealdata Read Ri data 4th byte - 4 left 2A56 STA (&70),Y 2A5A INY 2A55 LDA tubealdata Read ni data - 5th byte - S jeit 2ASE STA (&70 ,r 2A60 INY ZASt Ink tubealdata Read at data - 6th byte - 2 left 2A64 STA (&70).Y 2A6~ INY 2A67 LDA tubenidata Read Ri data - 7th byte - 1 left 2A6A STA (&70) .Y 2A6c Iwc 2A6fl LDA tubealdata Read ni data - 8th byte - buffer empty 2A70 STA (&70 ,Y (unless already re-filled by lee 2A72 INY 2A7S nnE &2AOE gait for sync unless on page boundary 2A~S INC &71 Increment high byte first 2A77 BPL &2A0E Check wrap around - b~1 transfer_loopt 2A79 LDA &~&40 Go back to bottorft of screen 2A7B STA &71 by resettin4 hi byte 2A7D mm &2A0E Branch to transfer_loopi- - - alway5
at? OSWORn - programs CaT controller. handles initialisation
onward fc 2A7F JsR get112data Get CaT controller tegister number 2Ae2 ~r &2A90 Return on 'FE 2Aa4 STA 'rEDO write 6845 CRTC address register 2AS7 JSfl getfldata Get data byte for 6945 2AAA S~A &rECl write 6945 Cfl~C data register 2A9D JMP &2A7? Repeat until &rr received onward to 1 2A90 TAX Get cornand code 2A91 INX In it aFF? 2A92 nrc exit Yes! - finished 2A94 rRx Is it arE? 2A95 BNE &2Aoc bn, onward_fc_2 - initialise ~ouse code 2A97 SE: set interrn~t disable 2A9e LnA ir~1 Load oric;inal mt. 1 vector la-byte 2A~n S~A &2aeA Store in oldirqt+1 2A9E LDA irqvl+1 Load original mt - 1 vector hi-byte 2AA1 s,!A &2nen Store in oldirql+2 2AA4 LDA &~newirql+1 "OD 25e new_i~ low byte 2AA6 STA irqvt Stare in 'Rd vector low byte 2AA9 LDA *newirql fl&v 256 new_lrq high byte 2AAB STA irq;ri+1 Store in rRo} vector hiqh byte 2AAE CLI re-enable interrupts 2AAF LDA SO Enable user-port input 2n1 STA ~rE62 Store An up_rdvrt - userport data dir 2AB4 LDA &~&98 enable CB1, CB2 interru~ts 2As6 S?A artet wrtte interrupt enable register 2An9 LDA &FE6fl Read auxiliary control register values 2ABC AND Si leave PA, disable Pn latching a timers 2ABE STA aFE6B write auxiliary control register 2A01 LDA aFEEC Read peripheral control register 2AC4 AND #&F Clear Cal, can bits 2Ac6 STA &FESC write peripheral control register 2Ac9 JIW &2A7r J~ OSWORD_ic to wait for cormaends -onward fc 2 2ACC nix is it 'FO (intercept events~? 2ACD mm &2AE6 bne os~ord_te_3 - No, continue 2ACF LDA eventvec Yest~ - load event vector low byte 2AD2 STA oldevent+1 Store it 2An5 LDA eventvec+1 Load event vector high byte 2AD8 STA oldevent+2 store it 2ADB LDA Inewevent Mon 256 Load new event low byte 2ADn STA evontyoc Replace oriqinal 2AE0 LDA taewevent DIV 256 Load new event high byte 2AE2 STA aventwc+1 Replace original 2A&5 JMP &~A7r Jump o5word_fc to wait for cor-ands onword fc S 2AE6 "ix is it arc (waa write mouse port 2AE9 mm exit No! - continne 2AEB JMP &2A7r rest - next coninand exit 2AEE RTS return from OSIfORD ide event QAEF LDX &261A icix ram_status - mc status ret~d in x 2Ar2 WY *0 zero Y for no', 2Ar4 STY &29F6 zero the status~nding flag 2AF7 LDA faA Generate event 10 - wa result waiting -oldevent 2AF9 EQUB &4C JMP instruction - for saved_vector -event 10 Jump address of oriqinal event code 2AFA EQUB C -event_hi 2Arn EQUB 0 TWO KEY ROLLOVER pROC~SStflG DONE HERE ON VSYNC EVENT .evtntccde 2AFC CMP *4 Event 4 Cvmync)? 2AFE BNE &2AF9 Not - branch oldevent 2B00 LDA &29r6 Read Status~ndInq - FnC status 0/s? ~flOS BEQ &2308 no! - Continue 2B05 Jart &2AEF asa fdc_event to ret-pending FflC status -eventccdel 2308 JsR keyscan asa sHFT~cTRL scary at &2n7n snoB PH? save etatus flags on stack 250c LDA keyl Read current ~ey ~ressed 2HO~ Ann i&7F Clear top bit 2B10 PLP Recover statu3 flags from stack 2B11 pHP then re-save them again for SHIFT 2B12 BPL anere Branch no_etri if CTRL not pressed 2B~4 OFLA &~&8O CTRL was pressed - set top bit no ctrl 2316 TAX store current key in x 2B17 LnA key2 Read last key pressed 2B19 AND &~a7r Clear top bit 2pm Pt? Recall scan status for SHIFT neic nvc &2a20 Branch no_ahift if SMIFT not pressed 2a1E eRA isso SHIFT was pressed - set top bit no shift 2B20 ~AY store last key in Y 2B21 LDA *4 Re-load vsync event 2B2a asa &2AF9 Re-issue original event
The current key (if any in now in X - The top bit always set if CONTflOL was pressed, even when no other key was pressed. The previous key, (if any) is floe in Y - The top bit always set SHIFT waz pressed. even when there is no previous key press.
asyne_ca-and 2B26 asa read_n4 Read tube a4 data 2329 BEQ &~B7A exit if n4 - zero - finished 2n2n TAX store in x 2n2c flEx Decretnent n4 value 2B2D BNE &~ssE Pt4 was > 1 - go to asyne_mouse upnA~z 6845 CRTC CONTROL ksGISTEflS
r4-l .anync_cursor 2B2F JSR read_n4 Read tube aA data - get 6945 req. addr. 2BS2 STA &FEOO write 6045 CRTC address reginter 2BS5 asa read n4 Flead tube R4 data - get the data byte 2B30 STA 'FEC! write 6845 Cfl~C data register 283B JMP &2B26 aepeat async_cointand READ USERPORT AbiD TRANSFER DATA
r4~2 -async_mouse ZB3E flEX 2 - mouse 2n3F HIrE &2R64 flA was > 2 - go to asyne_leds 2B4i LDA arAX fl4 wan 2 - read arax 2544 pnp Store flags for z 2a45 LDA userport Read unerport 2B4S eLp Recover z flag 2a49 BEC &2n4F Not AKX, tr~ba11?-brancb asyric_mouse_1 2n45 ROL A AMX buttons ate top bits 2n4c Rot A so trove them to the bottom 2B4D ROL A 2B4E ROL A bits 5, 6 and 7 are now 0, 1. 2 &~async_mOuse 1 2B4F AND *7 mask off the buttons 2B51 EOR 57 invert the bits 2553 Jsn write_at write tube nidata to send to 1S~ 2B56 IDX 43 set count for 4 bytes of co-orda &~async_mouse 2 2n~S ~A &2e21,x acad monSeft!~hi.x 2953 asa write al write tube aldata - send mouse data 295E flEx from &2821 285r Ept &2958 four times So branch asyno_nouse_2 if inco~lete 2R61 abip &2n26 JMP async_cc~and
SET KEYBOARD STATUS AND LEns r4~3
-asyno leds 2BG4 DEX 2365 BNE &2526 z4>3 - read tube aqain at asyne_co-and 2B67 JsR read k4 Read tube nadata 2B6A TAX put in x 2n6n LDA saca set up FX 202 - write keyboard status 2B6D LDY #0 Y - 0, X paramter from RA 2n6F ask osbyte set keyboard statua according to R4 2B72 LDA t&76 set up FX lie 2874 JSR osbyte Set keyboard LEDs 2377 JKP &~B26 3)4? asyric_command
-exit 2B7A RTS
-keyscan scans shift and control key presses 2n7n etc clear carry and overflow flags to 2a7c CLV , indicate botb SHIFT+CTRL scan re~ired 297D a}qp (keyvec Exit through orig- Sibri vector routine,
WARNING! MASKABLE INTERRUPT CODE FOLLOWS
X and Y must be preserved here. The original contents of A are
preserved by the Has, in zero page &FC. 'rhia also must be
reloaded before exiting - with an RTI it we process the interrupt
. or if we j~ to the original vector because we're not interested
.newirql 2B00 LnA &FESD Load Ant flag register - in it 'muse? 2flS3 AND tale rnask-00011000 -cnl and c32 active edqe? 2B85 aflE &2n8c AL leant one - qo to new_ir~code 2n87 LDA &FC Not CB1 not Cfl2 - restore A, foraet it
.oldirql Drop thru to here on any other mt 2369 EQUB &40 JMP - for saved_original vector
-ir~1c saved it- address of oriq md code 2neA aRK
.ir~hi Zafin BRK
- new~ir~code 2360 STA &2e2A ~asked mt flags in RAM in itt_copy 2B6F LDA userport Load VIA input reg S - tracker ball? 2B92 STA s2c2n store it at orb_copy 2n95 AND fals Mask it - these bits always hi for ANX 2B97 OMP noth set?-if either low mINT be t~ball 2B99 BEQ &QnAA Yes! - AMX no new_ir~code2 ~fl9fl LnA *0 Mark as tracker ball by atorinq 0 QflSfl STA &2c27 in AMX to override default 2BA0 LDA IS y quad signal is different to default 2BA2 STA &2c28 store it in RAM - tn rousey~qnad 2BA5 ~A Islo and S quad signal is different too 2nA7 STA s2c29 store it in RAM in mouse_x_quad
-new_ir~code2 2BAA tDA &2c2A masked mt flaq req copy - ifr_copy 23AD Ann &~&1o 'qank with 00010000 is it x? 2nAF BEC &2BnF No! - must be Y, branch new~ir~cnde5 2BB1 LDA &2c2E Get pezi~heral control copy - fler_copy 2flR4 EOR lab Invert pos~neg edge bit 2flfle STA &2C2E Store in per_copy - update Pcn edge 23B9 LDA &2CSC toad x_edge - get edge triggering mode 2BBC FOR #aFF Invert it 2nnE STA &2c20 re-store in x_edge 2nd EOR &202B ouad sig, orb_copy, invert if pos edqe 2nc4 AND &2c2e X component in rnousejt~q'aad 2nc7 BNE &2flfl4 necrease? - Yes - branch new_iz~code3 2nc9 INC &2824 Increment the low byte - monse_x_lo 2ncc BNE &ZBDS and if that beco~s a - new~ir~code5 23CE INC &2823 Inc the bi~h edqe - TROUSC_x_hi too 2nn1 JMP &2BDF Jump to new~iz~code5 for Y component
new ir~code3 ~Bfl4 IDA &2824 Dec - so load the low eaqe - rouse_r_la 2nD1 BNE &23DC If not 0 jump new_ir~code4, skip 2~n9 nEC &2923 Decrement of mouse X hi
.new~ir~ccde4 2BDC DEC &2824 Decrement raouse X lo
.new~ir~code5 2BDF IDA a2C2A Read masked mt flag contents- ifr_copy 2BE2 AND &~a Is there any input from Y? 2nEc flRO &2C14 No! - jtirap new~ir~code8 2BE6 LDA a2C2E Get peripheral ctrl register - per_copy 2nES EOR &~&40 Invert pos~neg bit 2n~s STA &2C2E Update peripheral etri req - PC?_COPY 2nEE LDA &2c20 Get edqe triggering mode - y_edqe 2nF1 Eon SaFF myort It 2nF3 STA &2c2D Store in y_edge 2nF6 EOR &2c~B Quad 5143. Invert it pr's - orb.co~y 2BF9 AND s2c2S Look at mouse~~quad 2nFc "~y &2009 Incr~nt? - No! branch new~ir~codeG 2nrE INC &~S22 Incr~~nt as per X motise~~1o ZCOi mm s2c14 Not zero? - branch new~Ir~codee 2c0S INC &2821 Increment moune~~hi 2c06 axe &2C14 J~ new~ir~codea
-new~ir~code6 2C09 LDA &2e22 Decrement as per X - mouse~~1o 2COC mm &2c11 Not zero? - branch new~ir~code7 2c0E DEC &2621 Decrement rnouse~~hi
-new~{r~code7
2c11 nEC s2e22 Decrement mouse~~lo
-new~ir~codeS 2c14 LDA &FESC Read real peripheral control reqiater 2017 mm preserve the bo~tnm nibble but set 2c19 ORA &2c2E the remainder to our copy in pcr_Copy 2C10 STA aFEEC Re-write peripheral control register 'air LDA lila Load cHi and cB2 active edge bits 2021 STA &FEGD write IFR to clear our interrupt 2c24 Lak &rc Recover A to intorru~t entry state 2c26 nTr Return from interrnpt 2c27 -arAX EQUn aFF default is AMX (0 - Tracker) 2c28 .rncuseflr~qnad EQUB 1 0Th - AM)C, (OS - Tracker 2c2~ mouse_x_quad ECUB 4 AMX, (10 Tracker) 2c2A -ifr_copy flaic RAM copy of Ira state 2C2B -orb_copy BRK RAM copy of user port B 2C20 K_e~e BUK defines pos/neq edqe triggering 2c2t -y_eaqe BEUC detines p05/nag edge triqqerinq 2C2E -pcr_copy flRK Local copy of PCR osijord fe
2c2r RTS
NOTE:- A local copy of the pcripheral connrol register is
naintained at per_copy because someone Is reprograr~Inq the VIA when they shouldn't be, leading to mouse reversal suspect a Master 12a hardware prohlera (2?)
HAFW DISK OSWCflfl
-OSWORD fe
2C30 RTS not ir~1emented
-pad EQUB 0
t**~*~*~****t******* EMD OF CODE ~
It should be noted that major bugs exist in the OSWORD &FA code which are virtually guaranteed to cause problems when the function is called from DOS Plus. Users are therefore warned that they should proceed with extreme caution when testing new routines which call this code and should consider the following points if (i.e. when) problems are encountered.
First, the original designer of the code seerns to have been unaware of various differences between the three host machifles' MOS variables and functions. For example OSBYTE &n has no fundion in a model B or B+ but is cailed in the routine at &2517 to d'e& the current shadow setting. Also reading or writing the contents of ROMSEL at &FE30 may have undefined implications in a model B.
Worst than this however, is that certain areas in memory mapped I/C, specifically ACCCON at &PE34, are not common to all versions of host. An attempt to read ACCCON in any host except a Master produces a nonsense result. Although this is in itself harniless, the result of an attempt to write ACCCON in either a model B or B+ (as at &26E3) is totally unpredictable and will almost certainly cause an immediate crash.
The code shown here is downloaded from the 512's ROMS on either a hard or a soft break. It therefore does not vary with the host type and can be guaranteed to hang the system in a TnodeI B or B+ because of the instruction at &26E5 which attempts to re-instate ACCCON's contents as originally recorded at &251C.
In a Master 128 ACCCON is designated as read/write, but readers should be aware that in spite of this fact the CSWORD &FA routine is not reliable in a Master either. While investigating the disassembly
provides no clue as to a reason, in all the tests conducted by myself calling OSWORD &PA from DOS Plus hangs a Master 128 too!
In addition word transfers seem to be inconsistently unreliable. Single byte transfers of types 0 and I and page transfers (types 6 and 7) appear to be reliable provided that writing to ACCCON is prevented. However, word transfers from the 512 (type 2) sometimes do not function correctly, sometimes doing nothing at all (including the transfer) occasionally hanging the system.
On balance however, type two transfers probably function correctly more often than not. The fault is extremely obscure, but so far as testing has been able to determine, it appears to depend on a combination of both the host target address and the type of transfer performed the last time the routine was called.
The only consistent fact to emerge from lengthy tests is that if any specific type 2 transfer in a sequence of transfers does fail, it can be reproduced and will fail consistently unless one of the attendant conditions is changed. if this particular problem is encountered users are advised to avoid it if possible by changing the target address rather than anempting to find the cause.
OSWORD &FA code ZERO PAGE &~.oRKSPACE
&7o - LSB of parameter block in host RAM &71 - MSB of parameter block in host RAM &72 - storage of current paqed no~ number &73 - Storage of current shadow setting a74 Lsn of host RAM data address 675 - NS3 of host FIRM data address &76 - MSS of 1en~th of data to be transferred &77 - tse of lenqth of data to be transferred flOT~&~- rarameters &76 and &77 are NOT in error- They are reversed from the usual low-byte-high-byte format
Zero page 1105 variables &F4 - romnum NOS copy of the current PtOM nuraber Mos calls used by this code osbyte &FrF4
SHEILA ~ty mapped I/O addresses &FE30 - ronwel The paqe no'. select latch &FE34 - acecon The paged ROM access control
Initia1 entry to thin code is after all other poanibilitien have been exhausted, by tirst the SOS. then by 6502&~sYs- If the call is not an OSWORD aFA control is passed to the sos default handler, giving the familiar 'Bad corrinand error which is passed acroas the tube as described in chapter 4-
2500 CLa clear carry for tube claim 2501 nad a2505 branch to oswc~ tent - alwaya default_handler 2503 flRK Contains the address of the Has 2504 nRK unknown OSWORD' default handler
&~oswotd teat 2505 alP taFA 1 15 this an OSNORD &FA? 2S07 BEQ a250C Yes - branch OSWORD_confirrw~d 2509 CMP (&2503) No - it- to default_handler
&~OSWORD_confirmed 250c ST~ &70 Store low byte of paramter address 250E STY &71 store hi byte of parameter address 2510 PHA Stote A on the stack 2511 Ink &~&FB Set u~ OSBYTE 251 to read 2513 inX 40 the state of the host's currant 2515 WY &~&FF shadow/main RAM selection 2517 JSR osbyte Current settinq returned in x 2SlA STX &7a Store current shadow setting 251c LDA accoon Read contents of &FE34 in SHEILA 251r PHA Store it on the stack
-tube claim
2520 LDA jac? Load tube claim identifier (This
code pretends to be a video dine
2522 JSn tube_entry claim the tube
2525 SCC &2$20 Failed? - repeat till success
2527 WY $0 Index to para~ter 1
2529 LDA ('70) .Y Read total ni-er of parameters
2523 CMP &~&fl an - RAM access, jE paged RON access
252~ PEP Store flags - z - 0 means normal MM
252E LDA &F4 Read MOS co~y of curr- paqed flox nurter
2530 STA &72 Store in zero pa4C
2532 LDY &~&D rndex ot n~mory access byte parameter
2534 LDA (&70) ,Y Read ~mory access type byte
2536 TAX Transfer to x
253~ WY $2 Inde'r to host RAN address parameter
25S9 Ink (&7O~,Y need tsB of host memory addtess
25S3 STA &74 store in rero page base
25at INY Increment index
253E LDA &70) ,Y Read MSR of host memory address
2540 STA a75 store in zero page base
2542 PLP pnl1 flaqa stored at &2$2D
2543 BEQ a25a5 Branch on normal RAM access
2545 TXA Kernory access type byte to A
2546 pHA Store memory access type on stack
2547 nm 4&40 Isolate screen mnmOrv bit (Sm)
2549 BNE &255E Not ~ero means write screen RA)q only
254n TXA Recover access type byte aqain
254c AND &~&20 Inolate screen address bit (m~a}
254E UNE &2554 Not zero means use shadow screen
set main access 2550 rnx 40 zero in 'C 2552 EEC &2556 Branch select ram - always
-set ahadow access 2554 Wx *1 Set access for shadow screen
select rem 2556 LDA t&6c OSflr!E lOB sel. 3cr. for direct access 2558 asa osbyte on contents of 'C - 0 - rain, 1 - shadow 255a JMP '2577 Ju~ get_roTh_nun~er 255E rnA *&e4 OSBYTE 132 read top of user RAM (HIMEM) 2560 JSR osbyte ROturns X - low byte, Y - high byte 256j CPY laflO HI-i &E00o? Yes means shadow 256$ BNr &256F no - branch to shadow_test 2567 LDA #1 Load A with 1 2569 CKp &73 cor~are to current shadow setting 25~n nfl& &~554 Not equal branch to net-shadow_access 256D BEQ &2550 Branch set_main_access - a1~ays shadow-test 2S6F LDA *2 Load A with 2 2571 CMP &73 Co~are to current 5hadcw setting 257S BNE &2550 Not equal - ~ranch to set_main_access 251$ BEQ &2564 Branch to set_shadow_access - always .~et_rom nunber 2577 PM pull memory access typo trom stack 2576 TAX store in 'C 2579 AND &~&1O Isolate nOM type nunber (bit 4 2573 BNE &2565 Not zero - use clirrent no" nuriber 257D Tm Recover memory access type byte 257& Mm Isolate required RON nunber (bits 0-3) 2580 STA &F4 stare in MOS copy of ROM flo. 25B2 STA roawel Store at &FE30 in SHEILA - RON_nnrnher set 2565 ~~Y &~&A Index at transfer lenqth paraneter 2567 InA (&70) ,Y Read LSfl of transfer lenqth 25S~ STA &77 Store in zero page 2585 INY Increment index to parameter Sn 25S0 LDA (&7O~,Y Read NSa of transfer length Q5SE STA &76 Store in zero page 25g0 ORA &77 Check transfer length LSB NSfl - tero 2592 BNE &2596 Not zero - continue 2594 BEQ &2604 LSS = NSE - 0 means complete 2596 InA &77 Reload transter length Lse 2598 BEQ &259c Inteqral page transfer? 25SA Inc s76 No - Increment transfer length NSB 25~c my :ncrement index to flaraneter 'C 259t LDA (&70 ,Y Read transfer type (0 to 3, 6 or 7
set_transfer_type 259? PHA store transfer type on stack 25A0 IDA &7~ Reload transfer length Lsn 25~~ ~EC &25n5 It LSB - 0 transfer is whole paqsn 25A4 ILA 676 Load transfer length MSB 25A6 CMP #1 single page 25kg BNE &25n5 NC - it~s a multi-page 25AA PLA Recover tranater type from stack 25AS PRA and re-store for further time 25AC ~~~ Is it type 6 or 7 (256 byte transfer) 25AE BCC &25B5 Yes branch to get_address 2513 PTA Neither - qet transfer type 25n1 SEC Set the carry flag 25B2 SBC *6 subtract 6 25B4 PHA Store the resnit on the stack -get_address 2535 LDA &70 Load the low byte ~arareter address 25n~ CLC Clear carry 25n8 ADC #6 Add 6 25SA TAX Transfer to x 25nn LDA #0 Clear A 25an loc '71 Load the high byte parameter address 253F TAX Transfer to Y 25c0 PLA Recover the transfer type byte 2SC~ PHA and re-atore for further use 25c2 JSR tube_entry Call tube host code 25c5 LDX &77 LSB at transfer lenqth into r 25C7 PLA ~ecover transfer type 25c9 CLY 40 Clear Y 25CA CMP *0 Transfer type 0? Cl byte to host) 25cc BEQ &25EC Yes - branch to jur~~_type_0 250K CMP 41 Transfer type 1 (1 byte from host 2500 BEQ &2607 YES - branch to type_1_transfer 25D2 CMP #2 Transfer type 2 (2 bytes to host) 25D4 BEQ &261fr Yes - branch to type_2_transfer 25D6 CMP &~3 Transfer type 3 (2 bytes fror host 25DB BEQ &2e4A Yes - branch to type_a_transfer 2SDA CXP #6 ~ransfer type 6 (1 page to host S5~C BRQ i2SEG branch to it-_type_6 2Sn~ ~~~ *7 Transfer type 7 (i paqe from host) 26E0 BEC &25E9 Branch to j~_type_7 25E2 LDA #0 must be finished 25E4 flZO a2604 indirect jump to release tube
.jump_type_ 6 25E5 JMP &2675 Long jump to type_ 6_transfer
.jump_type_7 25n9 JMP &2eA3 Long j~ to type_7 transfer
.jump_type_C 25Ec JSR &2SF4 waste some time
-type_zero transfer transfers single bytes from 512 to host at 24~secs(byte 25FF LDA tubeR3data Read data from tube register 3 25r2 STA (&74).Y Store it at indexed host address 25F4 JsR &2er4 waste some time 25F7 INC &74 Increment host address low byte 2SF~ ~~~ I If we havgn~t crossed a page boundary 25FB INC &75 else incr~nt the addrems high byte 25Fn DEx Decrement the count 25FE BNE &2SEF Finished 256 bytea? No - Re~at 2600 DEC &'' Decrenent '(SB at length 2602 BNE '25FF and go back for the next byte 2604 CMP &26nA J~ to release_tube
type_1 transfer Transfers single byte. from host to 512 at 24 usecs/byte 2607 IDA (&74 ,Y Read data frO~ host memory 2S09 STA tubea3dnta Write it to tube register S 26OC JSR &26r4 waste some time 260? INC &74 IncreTmOnt host address low byte 2611 BNE &2615 If we haven~t crossed a page boundary 2613 INC &75 Incre~nt the boat addreaa high byte 2615 ~EX and decrement the count 2616 BNE &2607 and go back for the next byte 261e DEC &7~ I Decreemnnt MSfl of ~enqth 261k mm &2c07 I Not tern - not finished 261c JMP Jump to release_tubO type_2 transfer Transfers words from 512 to host at 26~secs~word 261r JsR &26F4 Waste some time
.2_bytes_in 2622 LDA tuben3data Read data from tube register 3 2625 STA (&74) ,Y Store it at indexed boat address 2627 INC &74 Increment host address low byte 2629 ~~E &2620 If we haven't crossed a page boundary 262E INC &75 Incre~nt the host addresss high byte 262D NOP Delay for 2 cycles 262F NOP Delay for 2 cycles 262r tnA t~benSdata Read data fr~ tube register 3 2632 STA (s74) ,Y Store it at indexed host address 2634 INC &74 morement host address low byte 2636 BNE i26aA If we haven~t crossed a page boundary 26a0 INC &75 Increment the high address byte 263A JSR &26F3 waste 12 clock cycles 263D NOP Delay for 2 cycles 263E NOP Delay for 2 cycles 263F DEX decrement the count 2640 DEX decrement the count 2641 BNE &2622 Not zero? branch for next 2 bytes 2643 DEC 576 else decrement the MSfl of length 2645 BNE &2622 Not zero? branch fro next 2 bytes 2647 JMP a26flA Jua~ to release_tube
type_3 transfer ?!ransfers words frOTh host to 512 at 2~jtseca~word 264A LDA (&74},Y Read data tr~ host rn-cry 264C STA tuben3data write it to tube register 3 2e4r INC &74 Increment host address low byte 2~5l DEC &2656 tf we haven't croaned a ~age boundary 2653 NOP Delay for 2 cycles 2654 B~R S265e Branch if page boundary crossed 2656 INC &75 rncrement the host address high byte 2656 ~~A a73 waste 5 cycles (loads shadow setting 265A ~~A (&74) ,Y Load tram indexed host a-cry 265C STA tubeaSdata write to tube regAster S 265? INC '74 Increment the low address byte 2661 BEQ &2666 If we haven't crossed a paqe boundary 2663 NOP Delay for 2 cycles 2664 BNE &2665 If "C haven't croased a page boundary 2666 INC &75 else increment the hi~h adarcan byte 2666 JSR &26F3 waste 12 clock cycles 266n DEX deore~nt the count 2G6c DEX decretment the count 266D ~~~ &264A Not zero? branch for next 2 bytes 266F DEC &76 else decrement the Msn of lenqth 2S71 BNE &2e4A Not zero? branch for next 2 bytes 2S7~ DEC &2EDA Branch to release_tube
-type_6_transfer Transfers 256 byte block from 512 to host at 1OLtnacs~byte 2675 3Sfl &26S4 waste some time
qet_tube_byte 2678 LDA tube~data Read data frorfl tube register 3 267B STA (&74),Y store it at indexed host address 2S7n NOP nelay for 2 clock cycles 267E NOP Delay for 2 clock cycles SelF NOP Delay for 2 clock cycles 2680 INY Increment the index neal BNE &267a Branch get_tube_byte if < 256 bytes 2683 CPX 40 Have we finished? 2605 BNE &269a No - Repeat for next page 2687 DEC &76 Decrement MSS of length 2689 BEC ~26DA Branch to release_tube
- RspeRTSaae Q6aB JSR &26cE Incr~nt 512 page address 266E LDA 46 2690 JMP &259r at- to set_transfer_type
set_type_0 2693 DEC '76 decrement MSB of length 2695 LDA &16 load LSB of length 2697 CMP Si Is this the last page? 2e99 BNE &266n No - branch to re~eRTSage 269B ASR &2sCe Incr~nt 512 page address 269E LDA *0 set type zero transfer 26A0 JMP &259F Jmp to set_transfer_type
-type_7 transfer 26A3 INA (&74 ,Y Read data fr~ hont netftory 26AS SXA tubensaeta write it to tube register 3 26A6 NOP Delay for 2 clock cycles 26A9 NOP Delar for 2 clock cycles 26AA NOP Delay for 2 clock cycles 26As INY Incrgrntnt index 26A0 BNE $26A3 branch type_7_transfer if C 256 bytea 26AE CPX to Is lenqth LSB - zero? 2630 ~~~ &26nE no - branch decrement_length_mb 26n2 DEC '76 Decrement ~ISfl of length 26n4 BEQ &2~DA If c~lnt, branch to release_tube
-set_type_7 2636 JSR &2~cE Increment 512 page address 26ns LDA &~7 set transter type 7 2633 JMP ~259F ~ to set_transfer_type
dacremant_length_lab 26~~ BEc &76 decrement MSB of length 26C0 LDA S1~ Load MSB of lenqth 26C2 CMP *1 ra this the last page? 26C6 JSR &26CE Increment 512 page address aec; LDA 41 Set transfer type 1 26CR JMP &259F JL- to set_transfer_type
increment_512_offset Increments the MSB of 512's offset and the host adeirean by one page
26CR INC &75 Increments the host address high byte QEDO INY #7 load index to parameter block 26D2 LDA (~7O~.Y Load MSB of 512 address 26n4 CLC Clear carry 26n5 ~~~ Add 1 page to 512's segment offset 26n7 STA c'70}.Y Store at MSB of 512 offset address 2GD9 RTS Return
release tube 26DA IDA &a87 Load A for tube release 26Dc JSR tube_entry Call tube host code 26Dr LDA &72 Load original current no.' n-er 26E1 CMP xs it consistent with NOS? 26E3 BEQ &26eA Yes it~s OK - leave it 26E5 STA &r4 No - restore ~40S copy of ROM ni-er 26E7 STA roTRSel and restore ~FE3O in sHErn& 26~A PLA Recover contents of ACCOON 26~~ STA accoon and store at &FE34 in SHEIUL 2EEE ~~X £70 Restore x 26F0 ~~Y all aestote Y 26F2 PEA Restore A 26F3 RTS exit 26F4 JSR ~2Sr3 Occupies 24 clock cycles in all
~ End of OSWO~ &FA code ***tt******t****r,***