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Elite on the BBC Micro

Version analysis of TT102

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

Code variations between these versions are shown below.

Name: TT102 Type: Subroutine Category: Keyboard Summary: Process function key, save key, hyperspace and chart key presses

Code variation 1 of 29A variation in the comments only

This variation is blank in the Disc (docked) version.

Cassette, Flight, 6502SP, Master, Electron

and update the hyperspace counter

Process function key presses, plus "@" (save commander), "H" (hyperspace), "D" (show distance to system) and "O" (move chart cursor back to current system). We can also pass cursor position deltas in X and Y to indicate that

Code variation 2 of 29A variation in the comments only

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Cassette, Flight, Docked, 6502SP, Master

Electron

the cursor keys or joystick have been used (i.e. the values that are returned by routine TT17).
the cursor keys have been used (i.e. the values that are returned by routine TT17).

Code variation 3 of 29A variation in the comments only

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

Docked, 6502SP, Master

This routine also checks for the "F" key press (search for a system), which applies to enhanced versions only.
Arguments:

Code variation 4 of 29A variation in the comments only

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Cassette, Flight, Docked, 6502SP, Master

Electron

A The internal key number of the key pressed (see p.142 of the Advanced User Guide for a list of internal key numbers)
A The internal key number of the key pressed (see p.40 of the Electron Advanced User Guide for a list of internal key numbers)
X The amount to move the crosshairs in the x-axis Y The amount to move the crosshairs in the y-axis Other entry points: T95 Print the distance to the selected system

Code variation 5 of 29Specific to an individual platform

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

Electron

.VKEYS EQUB func2 \ The key to press for showing view 1 (back) EQUB func3 \ The key to press for showing view 2 (left) EQUB func4 \ The key to press for showing view 3 (right)
.TT102

Code variation 6 of 29A variation in the comments only

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Cassette, Flight, Docked, 6502SP, Master

Electron

CMP #f8 \ If red key f8 was pressed, jump to STATUS to show the BNE P%+5 \ Status Mode screen, returning from the subroutine JMP STATUS \ using a tail call CMP #f4 \ If red key f4 was pressed, jump to TT22 to show the BNE P%+5 \ Long-range Chart, returning from the subroutine using JMP TT22 \ a tail call CMP #f5 \ If red key f5 was pressed, jump to TT23 to show the BNE P%+5 \ Short-range Chart, returning from the subroutine using JMP TT23 \ a tail call
CMP #func9 \ If FUNC-9 was pressed, jump to STATUS to show the BNE P%+5 \ Status Mode screen, returning from the subroutine JMP STATUS \ using a tail call CMP #func5 \ If FUNC-5 was pressed, jump to TT22 to show the BNE P%+5 \ Long-range Chart, returning from the subroutine using JMP TT22 \ a tail call CMP #func6 \ If FUNC-6 was pressed, jump to TT23 to show the BNE P%+5 \ Short-range Chart, returning from the subroutine using JMP TT23 \ a tail call

Code variation 7 of 29A variation in the comments only

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Cassette

Flight, Docked, 6502SP, Master

Electron

CMP #f6 \ If red key f6 was pressed, call TT111 to select the BNE TT92 \ system nearest to galactic coordinates (QQ9, QQ10) JSR TT111 \ (the location of the chart crosshairs) and jump to JMP TT25 \ TT25 to show the Data on System screen, returning \ from the subroutine using a tail call
CMP #f6 \ If red key f6 was pressed, call TT111 to select the BNE TT92 \ system nearest to galactic coordinates (QQ9, QQ10) JSR TT111 \ (the location of the chart crosshairs) and set ZZ to JMP TT25 \ the system number, and then jump to TT25 to show the \ Data on System screen (along with an extended system \ description for the system in ZZ if we're docked), \ returning from the subroutine using a tail call
CMP #func7 \ If FUNC-7 was pressed, call TT111 to select the BNE TT92 \ system nearest to galactic coordinates (QQ9, QQ10) JSR TT111 \ (the location of the chart crosshairs) and jump to JMP TT25 \ TT25 to show the Data on System screen, returning \ from the subroutine using a tail call
.TT92

Code variation 8 of 29A variation in the comments only

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Cassette, Flight, Docked, 6502SP, Master

Electron

CMP #f9 \ If red key f9 was pressed, jump to TT213 to show the BNE P%+5 \ Inventory screen, returning from the subroutine JMP TT213 \ using a tail call CMP #f7 \ If red key f7 was pressed, jump to TT167 to show the BNE P%+5 \ Market Price screen, returning from the subroutine JMP TT167 \ using a tail call
CMP #func0 \ If FUNC-0 was pressed, jump to TT213 to show the BNE P%+5 \ Inventory screen, returning from the subroutine JMP TT213 \ using a tail call CMP #func8 \ If FUNC-8 was pressed, jump to TT167 to show the BNE P%+5 \ Market Price screen, returning from the subroutine JMP TT167 \ using a tail call

Code variation 9 of 29A variation in the comments only

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Cassette, Flight, Docked, 6502SP, Master

Electron

CMP #f0 \ If red key f0 was pressed, jump to TT110 to launch our BNE fvw \ ship (if docked), returning from the subroutine using JMP TT110 \ a tail call
CMP #func1 \ If FUNC-1 was pressed, jump to TT110 to launch our BNE fvw \ ship (if docked), returning from the subroutine using JMP TT110 \ a tail call
.fvw

Code variation 10 of 29Specific to an individual platform

This variation is blank in the Disc (flight) and Disc (docked) versions.

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Cassette, 6502SP, Master

Electron

BIT QQ12 \ If bit 7 of QQ12 is clear (i.e. we are not docked, but BPL INSP \ in space), jump to INSP to skip the following checks \ for f1-f3 and "@" (save commander file) key presses
BIT QQ12 \ If bit 7 of QQ12 is clear (i.e. we are not docked, but BPL INSP \ in space), jump to INSP to skip the following checks \ for FUNC-2 to FUNC-4 and "@" (save commander file) key \ presses

Code variation 11 of 29Specific to an individual platform

This variation is blank in the Disc (flight) version.

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Cassette, Docked, 6502SP, Master

Electron

CMP #f3 \ If red key f3 was pressed, jump to EQSHP to show the BNE P%+5 \ Equip Ship screen, returning from the subroutine using JMP EQSHP \ a tail call CMP #f1 \ If red key f1 was pressed, jump to TT219 to show the BNE P%+5 \ Buy Cargo screen, returning from the subroutine using JMP TT219 \ a tail call
CMP #func4 \ If FUNC-4 was pressed, jump to EQSHP to show the BNE P%+5 \ Equip Ship screen, returning from the subroutine using JMP EQSHP \ a tail call CMP #func2 \ If FUNC-2 was pressed, jump to TT219 to show the BNE P%+5 \ Buy Cargo screen, returning from the subroutine using JMP TT219 \ a tail call

Code variation 12 of 29Related to an enhanced feature

Pressing "@" brings up the disc access menu in the enhanced versions.

See below for more variations related to this code.

This variation is blank in the Disc (flight) version.

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Cassette

Docked, 6502SP

Master

Electron

CMP #&47 \ If "@" was pressed, jump to SVE to save the commander BNE P%+5 \ file, returning from the subroutine using a tail call JMP SVE
CMP #&47 \ If "@" was not pressed, skip to nosave BNE nosave
CMP #&40 \ If "@" was not pressed, skip to nosave BNE nosave
CMP #&48 \ If "@" was pressed, jump to SVE to save the commander BNE P%+5 \ file, returning from the subroutine using a tail call JMP SVE

Code variation 13 of 29Related to an enhanced feature

See variation 12 above for details.

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

Docked, 6502SP, Master

JSR SVE \ "@" was pressed, so call SVE to show the disc access \ menu BCC P%+5 \ If the C flag was set by SVE, then we loaded a new JMP QU5 \ commander file, so jump to QU5 to restart the game \ with the newly loaded commander JMP BAY \ Otherwise the C flag was clear, so jump to BAY to go \ to the docking bay (i.e. show the Status Mode screen) .nosave

Code variation 14 of 29Specific to an individual platform

This variation is blank in the Disc (flight) version.

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Cassette, Docked, 6502SP, Master

Electron

CMP #f2 \ If red key f2 was pressed, jump to TT208 to show the BNE LABEL_3 \ Sell Cargo screen, returning from the subroutine using JMP TT208 \ a tail call .INSP
CMP #func3 \ If FUNC-3 was pressed, jump to TT208 to show the Sell BNE LABEL_3 \ Cargo screen, returning from the subroutine using a JMP TT208 \ tail call .INSP

Code variation 15 of 29Specific to an individual platform

This variation is blank in the Disc (docked) version.

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Cassette, Flight, 6502SP

Master

Electron

CMP #f1 \ If the key pressed is < red key f1 or > red key f3, BCC LABEL_3 \ jump to LABEL_3 (so only do the following if the key CMP #f3+1 \ pressed is f1, f2 or f3) BCS LABEL_3 AND #3 \ If we get here then we are either in space, or we are TAX \ docked and none of f1-f3 were pressed, so we can now JMP LOOK1 \ process f1-f3 with their in-flight functions, i.e. \ switching space views \ \ A will contain &71, &72 or &73 (for f1, f2 or f3), so \ set X to the last digit (1, 2 or 3) and jump to LOOK1 \ to switch to view X (rear, left or right), returning \ from the subroutine using a tail call
CMP #f1 \ If red key f1 was pressed, jump to BVIEW BEQ BVIEW CMP #f2 \ If red key f2 was pressed, jump to LVIEW BEQ LVIEW CMP #f3 \ If red key f3 was not pressed, jump to LABEL_3 to keep BNE LABEL_3 \ checking for which key was pressed LDX #3 \ Red key f3 was pressed, so set the view number in X to \ 3 for the right view EQUB &2C \ Skip the next instruction by turning it into \ &2C &A2 &02, or BIT &02A2, which does nothing apart \ from affect the flags .LVIEW LDX #2 \ If we jump to here, red key f2 was pressed, so set the \ view number in X to 2 for the left view EQUB &2C \ Skip the next instruction by turning it into \ &2C &A2 &01, or BIT &02A2, which does nothing apart \ from affect the flags .BVIEW LDX #1 \ If we jump to here, red key f1 was pressed, so set the \ view number in X to 1 for the rear view JMP LOOK1 \ Jump to LOOK1 to switch to view X (rear, left or \ right), returning from the subroutine using a tail \ call
STX T \ Store X in T so we can retrieve it after the following LDX #3 \ We are about to loop through the key presses for the \ four views, so set a counter in X, starting with a \ value of X = 3 (for the right view) .LOOKL CMP VKEYS-1,X \ If the key pressed does not match the value in VKEYS BNE P%+5 \ for view X, skip the following instruction JMP LOOK1 \ The key pressed matches the key in position X, so jump \ to LOOK1 to switch to view X (rear, left or right), \ returning from the subroutine using a tail call DEX \ Decrement the view number in X, so we start with view \ 3 (right), then work backwards through 2 (left) and \ 1 (rear) BNE LOOKL \ Loop back to check the next key until we have checked \ for f3, f2 and f1 LDX T \ Fetch the value of X that we stored in T above
.LABEL_3

Code variation 16 of 29A variation in the labels only

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

6502SP

\ In the 6502 Second Processor version, the LABEL_3 \ label is actually `` (two backticks), but that doesn't \ compile in BeebAsm and it's pretty cryptic, so instead \ this version sticks with the label LABEL_3 from the \ cassette version

Code variation 17 of 29Specific to an individual platform

When docked in the disc version, the screen-clearing and DOCKED printing is done here rather than in hyp and hy6, but the code is the same.

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Cassette, Flight, 6502SP, Electron

Docked

Master

CMP #&54 \ If "H" was pressed, jump to hyp to do a hyperspace BNE P%+5 \ jump (if we are in space), returning from the JMP hyp \ subroutine using a tail call
CMP #&54 \ If "H" was not pressed, jump to NWDAV5 to skip the BNE NWDAV5 \ following JSR CLYNS \ "H" was pressed, so clear the bottom three text rows \ of the upper screen, and move the text cursor to \ column 1 on row 21, i.e. the start of the top row of \ the three bottom rows LDA #15 \ Move the text cursor to column 15 (the middle of the STA XC \ screen) LDA #205 \ Print extended token 205 ("DOCKED") and return from JMP DETOK \ the subroutine using a tail call
LDA KL \ If "H" was not pressed, jump to NWDAV5 to skip the CMP #'H' \ following BNE NWDAV5 JMP hyp \ Jump to hyp to do a hyperspace jump (if we are in \ space), returning from the subroutine using a tail \ call

Code variation 18 of 29A variation in the labels only

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

Docked, 6502SP, Master

.NWDAV5

Code variation 19 of 29Specific to an individual platform

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Cassette, Flight, Docked, 6502SP, Electron

Master

CMP #&32 \ If "D" was pressed, jump to T95 to print the distance BEQ T95 \ to a system (if we are in one of the chart screens)
CMP #&44 \ If "D" was pressed, jump to T95 to print the distance BEQ T95 \ to a system (if we are in one of the chart screens)

Code variation 20 of 29Related to an enhanced feature

Pressing "F" in the enhanced versions when viewing a chart lets us search for systems by name.

See below for more variations related to this code.

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

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Docked, 6502SP

Master

CMP #&43 \ If "F" was not pressed, jump down to HME1, otherwise BNE HME1 \ keep going to process searching for systems
CMP #&46 \ If "F" was not pressed, jump down to HME1, otherwise BNE HME1 \ keep going to process searching for systems

Code variation 21 of 29Specific to an individual platform

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

6502SP, Master

LDA QQ12 \ If QQ12 = 0 (we are not docked), we can't search for BEQ t95 \ systems, so return from the subroutine (as t95 \ contains an RTS)

Code variation 22 of 29Related to an enhanced feature

See variation 20 above for details.

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

Docked, 6502SP, Master

LDA QQ11 \ If the current view is a chart (QQ11 = 64 or 128), AND #%11000000 \ keep going, otherwise return from the subroutine (as BEQ t95 \ t95 contains an RTS) JMP HME2 \ Jump to HME2 to let us search for a system, returning \ from the subroutine using a tail call .HME1
 STA T1                 \ Store A (the key that's been pressed) in T1

Code variation 23 of 29Specific to an individual platform

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Cassette, Flight, 6502SP, Master, Electron

Docked

LDA QQ11 \ If the current view is a chart (QQ11 = 64 or 128), AND #%11000000 \ keep going, otherwise jump down to TT107 to skip the BEQ TT107 \ following LDA QQ22+1 \ If the on-screen hyperspace counter is non-zero, BNE TT107 \ then we are already counting down, so jump to TT107 \ to skip the following
LDA QQ11 \ If the current view is a chart (QQ11 = 64 or 128), AND #%11000000 \ keep going, otherwise jump down to t95 to return from BEQ t95 \ the subroutine LDA QQ22+1 \ If the on-screen hyperspace counter is non-zero, BNE t95 \ then we are already counting down, so jump down to t95 \ to return from the subroutine
 LDA T1                 \ Restore the original value of A (the key that's been
                        \ pressed) from T1

Code variation 24 of 29Specific to an individual platform

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Cassette, Flight, Docked, 6502SP, Electron

Master

CMP #&36 \ If "O" was pressed, do the following three jumps, BNE ee2 \ otherwise skip to ee2 to continue
CMP #&4F \ If "O" was pressed, do the following three jumps, BNE ee2 \ otherwise skip to ee2 to continue
 JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
                        \ which will erase the crosshairs currently there

 JSR ping               \ Set the target system to the current system (which
                        \ will move the location in (QQ9, QQ10) to the current
                        \ home system

Code variation 25 of 29Other (e.g. bug fix, optimisation)

This might be a bug fix? If "O" is pressed in the advanced versions, then the target system is set to home, and the routine terminates, which is different to the other versions; they stick around for one more move of the cursor, so presumably this fixes a bug where pressing "O" might not always move the cursor exactly to the current system.

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Cassette, Flight, Docked, Electron

6502SP, Master

JSR TT103 \ Draw small crosshairs at coordinates (QQ9, QQ10), \ which will draw the crosshairs at our current home \ system
JMP TT103 \ Draw small crosshairs at coordinates (QQ9, QQ10), \ which will draw the crosshairs at our current home \ system, and return from the subroutine using a tail \ call
.ee2

 JSR TT16               \ Call TT16 to move the crosshairs by the amount in X
                        \ and Y, which were passed to this subroutine as
                        \ arguments

Code variation 26 of 29Specific to an individual platform

This variation is blank in the Disc (docked) version.

Cassette, Flight, 6502SP, Master, Electron

.TT107 LDA QQ22+1 \ If the on-screen hyperspace counter is zero, return BEQ t95 \ from the subroutine (as t95 contains an RTS), as we \ are not currently counting down to a hyperspace jump DEC QQ22 \ Decrement the internal hyperspace counter BNE t95 \ If the internal hyperspace counter is still non-zero, \ then we are still counting down, so return from the \ subroutine (as t95 contains an RTS) \ If we get here then the internal hyperspace counter \ has just reached zero and it wasn't zero before, so \ we need to reduce the on-screen counter and update \ the screen. We do this by first printing the next \ number in the countdown sequence, and then printing \ the old number, which will erase the old number \ and display the new one because printing uses EOR \ logic LDX QQ22+1 \ Set X = the on-screen hyperspace counter - 1 DEX \ (i.e. the next number in the sequence) JSR ee3 \ Print the 8-bit number in X at text location (0, 1) LDA #5 \ Reset the internal hyperspace counter to 5 STA QQ22 LDX QQ22+1 \ Set X = the on-screen hyperspace counter (i.e. the \ current number in the sequence, which is already \ shown on-screen) JSR ee3 \ Print the 8-bit number in X at text location (0, 1), \ i.e. print the hyperspace countdown in the top-left \ corner DEC QQ22+1 \ Decrement the on-screen hyperspace countdown BNE t95 \ If the countdown is not yet at zero, return from the \ subroutine (as t95 contains an RTS) JMP TT18 \ Otherwise the countdown has finished, so jump to TT18 \ to do a hyperspace jump, returning from the subroutine \ using a tail call
.t95

 RTS                    \ Return from the subroutine

.T95

                        \ If we get here, "D" was pressed, so we need to show
                        \ the distance to the selected system (if we are in a
                        \ chart view)

 LDA QQ11               \ If the current view is a chart (QQ11 = 64 or 128),
 AND #%11000000         \ keep going, otherwise return from the subroutine (as
 BEQ t95                \ t95 contains an RTS)

Code variation 27 of 29Related to the screen mode

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

6502SP

LDA #CYAN \ Send a #SETCOL CYAN command to the I/O processor to JSR DOCOL \ switch to colour 3, which is white in the chart view
 JSR hm                 \ Call hm to move the crosshairs to the target system
                        \ in (QQ9, QQ10), returning with A = 0

Code variation 28 of 29Specific to an individual platform

This variation is blank in the Master version.

Cassette, Flight, Docked, 6502SP, Electron

STA QQ17 \ Set QQ17 = 0 to switch to ALL CAPS
 JSR cpl                \ Print control code 3 (the selected system name)

 LDA #%10000000         \ Set bit 7 of QQ17 to switch to Sentence Case, with the
 STA QQ17               \ next letter in capitals

Code variation 29 of 29Related to Elite's use of the Tube

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Cassette, Flight, Docked, Electron

Master

6502SP

LDA #1 \ Move the text cursor to column 1 and down one line STA XC \ (in other words, to the start of the next line) INC YC
LDA #12 \ Print a line feed to move the text cursor down a line JSR TT26
LDA #10 \ Print a line feed to move the text cursor down a line JSR TT26 LDA #1 \ Move the text cursor to column 1 JSR DOXC JSR INCYC \ Move the text cursor down one line
 JMP TT146              \ Print the distance to the selected system and return
                        \ from the subroutine using a tail call