BBC Micro Elite

Dashboard: BUMP2 (6502SP version)

```       Name: BUMP2                                             [View in context]
Type: Subroutine
Category: Dashboard
Summary: Bump up the value of the pitch or roll dashboard indicator

Increase ("bump up") X by A, where X is either the current rate of pitch or
the current rate of roll.

The rate of pitch or roll ranges from 1 to 255 with 128 as the centre point.
This is the amount by which the pitch or roll is currently changing, so 1
means it is decreasing at the maximum rate, 128 means it is not changing,
and 255 means it is increasing at the maximum rate. These values correspond
to the line on the DC or RL indicators on the dashboard, with 1 meaning full
left, 128 meaning the middle, and 255 meaning full right.

If bumping up X would push it past 255, then X is set to 255.

If keyboard auto-recentre is configured and the result is less than 128, we
bump X up to the mid-point, 128. This is the equivalent of having a roll or
pitch in the left half of the indicator, when increasing the roll or pitch
should jump us straight to the mid-point.

Other entry points:

RE2+2                Restore A from T and return from the subroutine

.BUMP2

STA T                  \ Store argument A in T so we can restore it later

TXA                    \ Copy argument X into A

CLC                    \ Clear the C flag so we can do addition without the
\ C flag affecting the result

ADC T                  \ Set X = A = argument X + argument A
TAX

BCC RE2                \ If the C flag is clear, then we didn't overflow, so

LDX #255               \ We have an overflow, so set X to the maximum possible
\ value of 255

.RE2

BPL djd1               \ If X has bit 7 clear (i.e. the result < 128), then