[Coco] Assembly help

[Chad H]

I have modified the original 25 byte assembly loader for .BIN files to read
8K from &HC000 to &HDFFF, access &HFF40 to trigger a SCS line (Picked up by
a microcontroller that will switch to the next 8K bank section, then read in
the next bank.   Each bank beginning with the second in the sequence, will
have a byte ID at &HC000, incrementing to identify each bank.  If the loader
doesn't recognize the correct bank, it will access the &HFF40 again.
Unfortunately, my revised 512K pcb's are unusable due to footprint size
problem with the ULN2803 transistor array so I had to correct and order
another batch.

 

In the mean time, I have no way to test this modified code.  The SIGSEG,
SENDSIG and CHKSW sections are all new.  Everything else was from the
original.   This doubles the size of the code to 52 bytes, though that won't
be much of a issue since .BIN's can be any size if this works.  I'm hoping
someone can look it over for me, I was kinda throwing darts at it with the
use of the CMPA and BNE stuff.   I've looked at several assembly language
references, included some existing source listings and can't verify I'm
using these correctly.   Basically I'm using SEGID as a incremented
variable, which gets compared to register A, which is loaded from 49152
(&HC000).   Any help from you assembly gurus would be greatly appreciated!
Thanks.

 

 

                *.BIN single/multisegment bootloader for ROM Pak

                

                org         49152                    CoCo and compatibles
map in ROM Paks here

 

SEGID    equ        0

 

        * LOADER

BININ   LDX     #BINLOD         INIT XFER DATA ADDRESS OFFSET

                CLRB                                      RESET AND CLEAR
SEGMENT COUNTER

CHKBLK  LDA     ,X+             GET BLOCK TYPE BYTE (00 = PREAMBLE,
255=POSTAMBLE)

        BNE     ENDBIN          IF <>0 THEN MUST BE END OF .BIN DATA
(POSTAMBLE)

        LDY     ,X++            GET BLOCK LENGTH(Y)

        LDU     ,X++            GET BLOCK START ADDRESS(U)

XFER    LDA     ,X+             GET SOURCE BYTE(A) FROM X

        STA     ,U+             PUT BYTE(A) AT U

        CMPX            $E000                    REACHED END OF 8K SEGMENT?

        JSR SIGSEG                 GO SIGNAL FOR THE NEXT SEGMENT.

        LEAY    -1,Y            MOVED BLOCK?

        BNE     XFER            NO

        BRA     CHKBLK          CHECK NEXT BLOCK

SIGSEG  INC        SEGID                    INCREMENT SEGMENT COUNTER

SENDSIG              LDX        #$FF40                  SET ADDRESS FOR
TRIGGER

                LDA        ,X                            TRIGGER SCS LINE TO
MICROCONTROLLER

CHKSW LDX        49152                    SET ADDRESS FOR SEGMENT
IDENTIFICATION BYTE LOCATION

                LDA        ,X

                CMPA   #SEGID                 COMPARE WITH EXPECTED SEGMENT
IDENTIFIER

                BNE        SENDSIG                              SEND SIGNAL
AGAIN IF NOT YET EXPECTED SEGMENT

                LDX        #BINLOD                              RESET
POINTER TO BEGINNING OF NEXT SEGMENT

                RTS                                         RETURN TO
TRANSFER LOOP

ENDBIN  JMP     [2,X]           SKIP BLOCK LENGTH (0000) AND JUMP TO
EXECUTION ADDRESS

BINLOD  FCB     255

 

- Chad H

http://sites.google.com/site/cbhlab101/