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Elite on the BBC Micro

Version analysis of DIALS (Part 3 of 4)

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

Name: DIALS (Part 3 of 4) Type: Subroutine Category: Dashboard Summary: Update the dashboard: four energy banks Deep dive: The dashboard indicators

Code variation 1 of 11A variation in the comments only

This variation is blank in the Master version.

Cassette, Flight, Docked, 6502SP, Electron

This and the next section only run once every four iterations of the main loop, so while the speed, pitch and roll indicators update every iteration, the other indicators update less often.

Code variation 2 of 11Related to the Master version

The Master version updates all the dials on every iteration of the main loop, while the other versions only update the speed, pitch and roll indicators on every loop (the other indicators only update every four iterations of the main loop).

This variation is blank in the 6502 Second Processor and Master versions.

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, Electron

Docked

LDA MCNT \ Fetch the main loop counter and calculate MCNT mod 4, AND #3 \ jumping to rT9 if it is non-zero. rT9 contains an RTS, BNE rT9 \ so the following code only runs every 4 iterations of \ the main loop, otherwise we return from the subroutine
LDA MCNT \ Fetch the main loop counter and calculate MCNT mod 4, AND #3 \ jumping to R5-1 if it is non-zero. R5-1 contains an BNE R5-1 \ RTS, so the following code only runs every 4 \ iterations of the main loop, otherwise we return from \ the subroutine
 LDY #0                 \ Set Y = 0, for use in various places below

Code variation 3 of 11Related to the Electron version

Dashboard indicators in the Electron version don't change colour, as the dashboard is monochrome.

See below for more variations related to this code.

This variation is blank in the Electron version.

Cassette, Flight, Docked, 6502SP, Master

JSR PZW \ Call PZW to set A to the colour for dangerous values \ and X to the colour for safe values STX K \ Set K (the colour we should show for high values) to X \ (the colour to use for safe values) STA K+1 \ Set K+1 (the colour we should show for low values) to \ A (the colour to use for dangerous values) \ The above sets the following indicators to show red \ for low values and yellow/white for high values, which \ we use not only for the energy banks, but also for the \ shield levels and current fuel

Code variation 4 of 11A variation in the comments only

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, Docked, Electron

6502SP, Master

LDX #3 \ Set up a counter in X so we can zero the four bytes at \ XX12, so we can then calculate each of the four energy \ banks' values before drawing them later
LDX #3 \ Set up a counter in X so we can zero the four bytes at \ XX15, so we can then calculate each of the four energy \ banks' values before drawing them later

Code variation 5 of 11Related to the Electron version

See variation 3 above for details.

This variation is blank in the Electron version.

Cassette, Flight, Docked, 6502SP, Master

STX T1 \ Set T1 to 3, the threshold at which we change the \ indicator's colour
.DLL23

Code variation 6 of 11Minor and very low-impact

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Cassette, Flight, Docked, Electron

6502SP, Master

STY XX12,X \ Set the X-th byte of XX12 to 0
STY XX15,X \ Set the X-th byte of XX15 to 0
 DEX                    \ Decrement the counter

 BPL DLL23              \ Loop back for the next byte until the four bytes at
                        \ XX12 are all zeroed

 LDX #3                 \ Set up a counter in X to loop through the 4 energy
                        \ bank indicators, so we can calculate each of the four
                        \ energy banks' values and store them in XX12

Code variation 7 of 11Related to the screen mode

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, Docked, 6502SP, Master

Electron

LDA ENERGY \ Set A = Q = ENERGY / 4, so they are both now in the LSR A \ range 0-63 (so that's a maximum of 16 in each of the LSR A \ banks, and a maximum of 15 in the top bank)
LDA ENERGY \ Set A = Q = ENERGY / 2, so they are both now in the LSR A \ range 0-127 (so that's a maximum of 32 in each of the \ banks, and a maximum of 31 in the top bank)
 STA Q                  \ Set Q to A, so we can use Q to hold the remaining
                        \ energy as we work our way through each bank, from the
                        \ full ones at the bottom to the empty ones at the top

.DLL24

Code variation 8 of 11Related to the screen mode

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, Docked, 6502SP, Master

Electron

SEC \ Set A = A - 16 to reduce the energy count by a full SBC #16 \ bank
SEC \ Set A = A - 32 to reduce the energy count by a full SBC #32 \ bank
 BCC DLL26              \ If the C flag is clear then A < 16, so this bank is
                        \ not full to the brim, and is therefore the last one
                        \ with any energy in it, so jump to DLL26

 STA Q                  \ This bank is full, so update Q with the energy of the
                        \ remaining banks

Code variation 9 of 11Related to the screen mode

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, Docked

6502SP, Master

Electron

LDA #16 \ Store this bank's level in XX12 as 16, as it is full, STA XX12,X \ with XX12+3 for the bottom bank and XX12+0 for the top
LDA #16 \ Store this bank's level in XX15 as 16, as it is full, STA XX15,X \ with XX15+3 for the bottom bank and XX15+0 for the top
LDA #32 \ Store this bank's level in XX12 as 32, as it is full, STA XX12,X \ with XX12+3 for the bottom bank and XX12+0 for the top
 LDA Q                  \ Set A to the remaining energy level again

 DEX                    \ Decrement X to point to the next bank, i.e. the one
                        \ above the bank we just processed

 BPL DLL24              \ Loop back to DLL24 until we have either processed all
                        \ four banks, or jumped out early to DLL26 if the top
                        \ banks have no charge

 BMI DLL9               \ Jump to DLL9 as we have processed all four banks (this
                        \ BMI is effectively a JMP as A will never be positive)

.DLL26

Code variation 10 of 11Minor and very low-impact

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Cassette, Flight, Docked, Electron

6502SP, Master

LDA Q \ If we get here then the bank we just checked is not STA XX12,X \ fully charged, so store its value in XX12 (using Q, \ which contains the energy of the remaining banks - \ i.e. this one)
LDA Q \ If we get here then the bank we just checked is not STA XX15,X \ fully charged, so store its value in XX15 (using Q, \ which contains the energy of the remaining banks - \ i.e. this one)
                        \ Now that we have the four energy bank values in XX12,
                        \ we can draw them, starting with the top bank in XX12
                        \ and looping down to the bottom bank in XX12+3, using Y
                        \ as a loop counter, which was set to 0 above

.DLL9

Code variation 11 of 11Minor and very low-impact

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Cassette, Flight, Docked, Electron

6502SP, Master

LDA XX12,Y \ Fetch the value of the Y-th indicator, starting from \ the top
LDA XX15,Y \ Fetch the value of the Y-th indicator, starting from \ the top
 STY P                  \ Store the indicator number in P for retrieval later

 JSR DIL                \ Draw the energy bank using a range of 0-15, and
                        \ increment SC to point to the next indicator (the
                        \ next energy bank down)

 LDY P                  \ Restore the indicator number into Y

 INY                    \ Increment the indicator number

 CPY #4                 \ Check to see if we have drawn the last energy bank

 BNE DLL9               \ Loop back to DLL9 if we have more banks to draw,
                        \ otherwise we are done

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