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BBC Micro Elite

Start and end: DFAULT (6502SP version)

Name: DFAULT [View in context] Type: Subroutine Category: Start and end Summary: Reset the current commander data block to the last saved commander
.DFAULT LDX #NT%+8 \ The size of the last saved commander data block is NT% \ bytes, and it is preceded by the 8 bytes of the \ commander name (seven characters plus a carriage \ return). The commander data block at NAME is followed \ by the commander data block, so we need to copy the \ name and data from the "last saved" buffer at NA% to \ the current commander workspace at NAME. So we set up \ a counter in X for the NT% + 8 bytes that we want to \ copy .QUL1 LDA NA%-1,X \ Copy the X-th byte of NA%-1 to the X-th byte of STA NAME-1,X \ NAME-1 (the -1 is because X is counting down from \ NT% + 8 to 1) DEX \ Decrement the loop counter BNE QUL1 \ Loop back for the next byte of the commander data \ block STX QQ11 \ X is 0 by the end of the above loop, so this sets QQ11 \ to 0, which means we will be showing a view without a \ boxed title at the top (i.e. we're going to use the \ screen layout of a space view in the following) JSR CHECK \ Call the CHECK subroutine to calculate the checksum \ for the current commander block at NA%+8 and put it \ in A CMP CHK \ Test the calculated checksum against CHK IF _REMOVE_CHECKSUMS NOP \ If we have disabled checksums, then ignore the result NOP \ of the comparison and fall through into the next part ELSE BNE P%-6 \ If commander check is enabled and the calculated \ checksum does not match CHK, then loop back to repeat \ the check - in other words, we enter an infinite loop \ here, as the checksum routine will keep returning the \ same incorrect value ENDIF \JSR BELL \ This instruction is commented out in the original \ source. It would make a standard system beep EOR #&A9 \ X = checksum EOR &A9 TAX LDA COK \ Set A to the competition flags in COK CPX CHK2 \ If X = CHK2, then skip the next instruction BEQ tZ ORA #%10000000 \ Set bit 7 of A to indicate this commander file has \ been tampered with .tZ ORA #4 \ Set bit 2 of A to denote this is the 6502 second \ processor version (which is the same bit as for the \ disc version) STA COK \ Store the updated competition flags in COK RTS \ Retirn from the subroutine