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Dashboard: BUMP2

[BBC Micro cassette version]

Name: BUMP2 [Show more] Type: Subroutine Category: Dashboard Summary: Bump up the value of the pitch or roll dashboard indicator
Context: See this subroutine in context in the source code Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DOKEY calls BUMP2 * REDU2 calls via RE2+2

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 \ jump to RE2 to auto-recentre and return the result LDX #255 \ We have an overflow, so set X to the maximum possible \ value of 255 .RE2 BPL RE3+2 \ If X has bit 7 clear (i.e. the result < 128), then \ jump to RE3+2 in routine REDU2 to do an auto-recentre, \ if configured, because the result is on the left side \ of the centre point of 128 \ Jumps to RE2+2 end up here LDA T \ Restore the original argument A from T into A RTS \ Return from the subroutine