Skip to navigation

Elite on the BBC Micro

Version analysis of MESS

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

Code variations between these versions are shown below.

Name: MESS Type: Subroutine Category: Text Summary: Display an in-flight message
Display an in-flight message in capitals at the bottom of the space view, erasing any existing in-flight message first. Arguments: A The text token to be printed
.MESS

Code variation 1 of 6Related to the screen mode

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

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

Master

6502SP

PHA \ Store A on the stack so we can restore it after the \ the call to DOCOL LDX QQ11 \ If this is the space view, skip the following BEQ P%+5 \ instruction JSR CLYNS \ 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 #21 \ Move the text cursor to row 21 STA YC LDA #YELLOW \ Switch to colour 1, which is yellow STA COL
PHA \ Store A on the stack so we can restore it after the \ the call to DOCOL LDA #YELLOW \ Send a #SETCOL YELLOW command to the I/O processor to JSR DOCOL \ switch to colour 1, which is yellow PLA \ Restore A from the stack
 LDX #0                 \ Set QQ17 = 0 to switch to ALL CAPS
 STX QQ17

Code variation 2 of 6Related to an advanced feature

The original versions display in-flight messages at column 9 on row 22, at the bottom of the screen. The advanced versions go one better and centre their in-flight messages on screen, rather than always starting them at column 9.

See below for more variations related to this code.

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

Cassette, Flight, Docked, Electron

Master

6502SP

LDY #9 \ Move the text cursor to column 9, row 22, at the STY XC \ bottom middle of the screen, and set Y = 22 LDY #22 STY YC
LDA messXC \ Move the text cursor to column messXC, in case we STA XC \ jump to me1 below to erase the current in-flight \ message (whose column we stored in messXC when we \ called MESS to put it there in the first place) PLA \ Restore A from the stack LDY #20 \ Set Y = 20 for setting the message delay below
PHA \ Store A on the stack so we can restore it after the \ the calls to DOXC and DOYC LDA messXC \ Move the text cursor to column messXC, in case we JSR DOXC \ jump to me1 below to erase the current in-flight \ message (whose column we stored in messXC when we \ called MESS to put it there in the first place) LDA #22 \ Move the text cursor to row 22, and set Y = 22 TAY JSR DOYC PLA \ Restore A from the stack
 CPX DLY                \ If the message delay in DLY is not zero, jump up to
 BNE me1                \ me1 to erase the current message first (whose token
                        \ number will be in MCH)

Code variation 3 of 6Related to the Master version

The Master version flashes in-flight messages 10% more quickly than the other versions.

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

Cassette, Flight, Docked, 6502SP, Electron

Master

STY DLY \ Set the message delay in DLY to 22
STY DLY \ Set the message delay in DLY to 20
 STA MCH                \ Set MCH to the token we are about to display

Code variation 4 of 6Related to an advanced feature

See variation 2 above for details.

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

6502SP, Master

\ Before we fall through into mes9 to print the token, \ we need to work out the starting column for the \ message we want to print, so it's centred on-screen, \ so the following doesn't print anything, it just uses \ the justified text mechanism to work out the number of \ characters in the message we are going to print LDA #%11000000 \ Set the DTW4 flag to %11000000 (justify text, buffer STA DTW4 \ entire token including carriage returns) LDA de \ Set the C flag to bit 1 of the destruction flag in de LSR A LDA #0 \ Set A = 0 BCC P%+4 \ If the destruction flag in de is not set, skip the \ following instruction LDA #10 \ Set A = 10 STA DTW5 \ Store A in DTW5, so DTW5 (which holds the size of the \ justified text buffer at BUF) is set to 0 if the \ destruction flag is not set, or 10 if it is (10 being \ the number of characters in the " DESTROYED" token) LDA MCH \ Call TT27 to print the token in MCH into the buffer JSR TT27 \ (this doesn't print it on-screen, it just puts it into \ the buffer and moves the DTW5 pointer along, so DTW5 \ now contains the size of the message we want to print, \ includint the " DESTROYED" part if that's going to be \ included) LDA #32 \ Set A = (32 - DTW5) / 2 SEC \ SBC DTW5 \ so A now contains the column number we need to print LSR A \ our message at for it to be centred on-screen (as \ there are 32 columns) STA messXC \ Store A in messXC, so when we erase the message via \ the branch to me1 above, messXC will tell us where to \ print it

Code variation 5 of 6Specific to an individual platform

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

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

Master

6502SP

STA XC \ Move the text cursor to column messXC
JSR DOXC \ Move the text cursor to column messXC

Code variation 6 of 6Related to an advanced feature

See variation 2 above for details.

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

6502SP, Master

JSR MT15 \ Call MT15 to wwitch to left-aligned text when printing \ extended tokens disabling the justify text setting we \ set above LDA MCH \ Set MCH to the token we are about to display
                        \ Fall through into mes9 to print the token in A

RSS Feed