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Elite on the BBC Micro

Version analysis of DIALS (Part 1 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 1 of 4) Type: Subroutine Category: Dashboard Summary: Update the dashboard: speed indicator Deep dive: The dashboard indicators
This routine updates the dashboard. First we draw all the indicators in the right part of the dashboard, from top (speed) to bottom (energy banks), and then we move on to the left part, again drawing from top (forward shield) to bottom (altitude). This first section starts us off with the speedometer in the top right.
.DIALS

Code variation 1 of 5Specific to an individual platform

This variation is blank in the Cassette, Disc (flight), Disc (docked), Master and Electron versions.

6502SP

LDA #%00000001 \ Set 6522 System VIA interrupt enable register IER STA VIA+&4E \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt, \ which comes from the keyboard)

Code variation 2 of 5Specific to an individual platform

This variation is blank in the Cassette, Disc (flight), Disc (docked), 6502 Second Processor and Electron versions.

Master

LDA #%00001111 \ Set bits 1 and 2 of the Access Control Register at STA VIA+&34 \ SHEILA &34 to switch screen memory into &3000-&7FFF LDA #1 \ Set location &DDEB to 1. This location is in HAZEL, STA &DDEB \ which contains the filing system RAM space, though \ I'm not sure what effect this has

Code variation 3 of 5Related 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 #&D0 \ Set SC(1 0) = &78D0, which is the screen address for STA SC \ the character block containing the left end of the LDA #&78 \ top indicator in the right part of the dashboard, the STA SC+1 \ one showing our speed JSR PZW \ Call PZW to set A to the colour for dangerous values \ and X to the colour for safe values
LDA #&A0 \ Set SC(1 0) = &71A0, which is the screen address for STA SC \ the character block containing the left end of the LDA #&71 \ top indicator in the right part of the dashboard, the STA SC+1 \ one showing our speed JSR PZW2 \ Call PZW2 to set A to the colour for dangerous values \ and X to the colour for safe values, suitable for \ non-striped indicators
LDA #&F0 \ Set SC(1 0) = &76F0, which is the screen address for STA SC \ the character block containing the left end of the LDA #&76 \ top indicator in the right part of the dashboard, the STA SC+1 \ one showing our speed

Code variation 4 of 5Related to the screen mode

This variation is blank in the Electron version.

Cassette, Flight, Docked, 6502SP, Master

STX K+1 \ Set K+1 (the colour we should show for low values) to \ X (the colour to use for safe values) STA K \ Set K (the colour we should show for high values) to \ A (the colour to use for dangerous values) \ The above sets the following indicators to show red \ for high values and yellow/white for low values LDA #14 \ Set T1 to 14, the threshold at which we change the STA T1 \ indicator's colour
 LDA DELTA              \ Fetch our ship's speed into A, in the range 0-40

Code variation 5 of 5Related 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

\LSR A \ Draw the speed indicator using a range of 0-31, and JSR DIL-1 \ increment SC to point to the next indicator (the roll \ indicator). The LSR is commented out as it isn't \ required with a call to DIL-1, so perhaps this was \ originally a call to DIL that got optimised
JSR DIL-1 \ Draw the speed indicator using a range of 0-31, and \ increment SC to point to the next indicator (the roll \ indicator)
JSR DIL \ Draw the speed indicator using a range of 0-31, and \ increment SC to point to the next indicator (the roll \ indicator)
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