Roland checksum – how to

[human fly]

here are the notes i found for calculating the Roland checksum
-cribbed Eddie Lotter’s webpage, abbreviated –
(early devices, don’t know if it changes for anything more recent)
——————————————————————
The checksum is a value derived from the address and the data. The
device will also calculate it from the address and data it receives
and check its checksum against the one you supply. If they match then
it has received the SysEx message correctly.

example: if the address is 40h 00h 04h and the data is 64h
Here’s how the checksum is derived:
——————————————————————
method #1:
Add each of the values, one by one. Each time the value exceeds 127 (7Fh)
subtract 128 (80h) from it. Finally subtract the resultant value from 128
and you have your checksum!

In hexadecimal: (I won’t put h after each value for clarity)
40 + 00 = 40 (Surprise!)
40 + 04 = 44
44 + 64 = A8 ( A8 > 7F so…)
A8 – 80 = 28
80 – 28 = 58 (The checksum is 58h)

In decimal:
64 + 0 = 0
64 + 4 = 68
68 + 100 = 168 ( 168 > 127 so…)
168 – 128 = 40
128 – 40 = 88 (The checksum is 88)

To show what is actually happening I’ll show you the last line in binary:

10000000 – 00101000 = 01011000

According to the manual “The error checking process uses a checksum that
provides a bit pattern where the least significant 7 bits are zero when
values for an address, [data], and that checksum are summed.”
The low bits in binary are on the right. In the binary calculation above,
add the address, data and checksum and you get back to 128, which has all
seven lower bits clear:

address & data + checksum = 128
00101000 + 01011000 = 10000000

Note that in this example, while summing the values we exceeded 127 and
had to subtract 128. This is not always necessary, as long as the
summed values do not exceed 127.

If the sum of the values comes to 128 then I’m sure it is clear that
the checksum is 128! Look at the arithmetic:
x + y = 128 ( 128 > 127 so…)
128 – 128 = 0
128 – 0 = 128 (The checksum is 128)

If anything in this document is ambiguous or unclear, please let me know
so that I can improve it for everyone’s benefit.

Eddie
lotter@cc.und.ac.za
—————————————————————————
method #2: (note: i prefer this, easier)

The manual shows a different method which involves slightly more complicated arithmatic.
In essence it involves adding all the values together, dividing by 128 and subtracting the remainder from 128. Thus:

1. Convert hex to decimal:
40h = 64
11h = 17
00h = 0
41h = 65
63h = 99

2. Add values:
64 + 17 + 0 + 65 + 99 = 245

3. Divide by 128
245 / 128 = 1 remainder 117

4. Subtract remainder from 128
128 – 117 = 11

5. Covert to hex:
11 = 0Bh

(Eddie Lotter)
——————————
eg: (aa+aa+aa+dd+dd)/128 > take remainder
128-(remainder)=checksum

>check that against method#1:
1. Convert hex to decimal:
40h = 64
11h = 17
00h = 0
41h = 65
63h = 99

2. Add values, keeping result under 128:
64 + 17 = 81
81 + 0 = 81
81 + 65 = 146 ( 146 – 128 = 18 )
18 + 99 = 117

3. Subtract answer from 128
128 – 117 = 11

4. Covert to hex:
11 = 0Bh
—————————————————–
note: once you’ve calculated the checksum, you will
notice that it proceeds in inverse direction to the
value;
ie: as the value increments, the checksum decrements.

hope this is useful.

[Possemo]

Here is a demo panel with one slider (cutoff of part1). One script for all parameters.

To specify the address the following fields are used:

addresspart1 = Custom modulator index group
addresspart2 = A custom group name
addresspart3 = Custom modulator index

All values in decimal.

Use at your own risk. I won’t be responsible for any damage this will do on whatever software/hardware.

• This reply was modified 6 years, 1 month ago by Possemo.

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[Possemo]

An improved version. On this one the address in the sysexstring is done with global variables so the sysex-field will allways be the same. You just have to enter the address in the Custom fields – as said:

addresspart1 = Custom modulator index group
addresspart2 = A custom group name
addresspart3 = Custom modulator index

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[human fly]

don’t worry, not sending it to anything; can use midiox anyway, with
loopbe1.

ok, so i’ve got that up in front of me now. i recognise the header with
manuf, deviceID, midiCh etc. and then you have k0, k1, k2, xx, k3, F7,
where: k0/k1/k2 is the address, xx is the variable value, and k3 is the
checksum.

looking down the properties panel, i see:

‘luaModulatorGetValueForMIDI’ with ‘calcChecksum’ selected. i see there’s
a list of options: none, calcChecksul, and a few others.

i hadn’t looked at this before tbh. nor did i check out the icons
and what they do. did you add these methods or are they standard?
let’s try ‘Edit method’ to see what that looks like:
———————————————————————
calcChecksum = function(modulator, numericModulatorValue)

— assign address fields
addressPart1=modulator:getPropertyInt(“modulatorCustomIndexGroup”)
addressPart2=modulator:getPropertyInt(“modulatorCustomNameGroup”)
addressPart3=modulator:getPropertyInt(“modulatorCustomIndex”)

— sum is the addition of addresses and value. I used decimal here, 25hex is 37decimal.
sum=addressPart1+addressPart2+addressPart3+numericModulatorValue

— if sum is greater than 127 then do..
if sum>127 then sum=127-sum end

checksum=128-sum

panel:setProperty(“panelGlobalVariables”,addressPart1..”:”..addressPart2..”:”..addressPart3..”:”..checksum..”:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0″,false)

return numericModulatorValue

end
————————————————————
ah! ok, so that appears to be a built-in instruction, calcChecksum, right?
and the 2nd calculation method i described earlier…okaaay..i see that;
it just looks so different from what i’m used to.

‘–‘ are ren ‘d comments…

let’s have a picture – see attachment(hopefully will upload)
i don’t really understand the last bit, ‘set property’ etc.
because i don’t speaka da lingo yet.

so k0…k3
i substitute k0, K1, k2 with the address?

i’ve also seen checksum in the JayVee panel with ‘z5’ at the
checksum position. is that the same method? i’d better have a
fresh look at that.

thanks for your help+patience !

• This reply was modified 6 years, 1 month ago by human fly.

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[Possemo]

No, this is not built in. Panel developers have to do that themselves.

yes, — are remarks

the last bit sets the Ctrlr global variables. I think Roman made this to get the Matrix-1000 panel working, so it is a bit of an awkward feature but very handy in this case:

panel:setProperty(“panelGlobalVariables”,addressPart1..”:”..addressPart2..”:”..addressPart3..”:”..checksum..”:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0″,false)

This sets the first four global variables, the rest is set to “0”. When you use the global variables in the SysexString k0 is the first variable, k1 the second etc.

Screenshot attached shows you the fields I used for the address:

addressPart1=modulator:getPropertyInt(“modulatorCustomIndexGroup”)
addressPart2=modulator:getPropertyInt(“modulatorCustomNameGroup”)
addressPart3=modulator:getPropertyInt(“modulatorCustomIndex”)

Just fyi, the second screenshot shows the global variables, but there you can do nothing else but looking at how they are set.

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[human fly]

ok i found those first ones. i wouldn’t have found the
Panel Global variables.

it seems like a really complicated way of doing a simple thing 🙂

do you have the JayVee Family panel? have a look at the sysex
line in that: i can’t see a lua. the checksum position has
‘z5’. and that seems to be it. maybe z5 is a shorthand for the
checksum lua? i ‘ve never tested that panel.

• This reply was modified 6 years, 1 month ago by human fly.

[Possemo]

I just looked into the JayVee panel. Yes you are right. Indeed it looks like z5 triggers a builtin Roland checksum calculator.

Well, that’s one of the problems of Ctrlr – so much features and zero documentation.

So, forget my approach, it’s completely obsolete…

[human fly]

well thank you for the introduction to those lua tabs.
i need to take some time out to study that.
don’t know how the JayVee author found out about z5.
i’m relieved if it’s just that !

absolutely true, there needs to be some proper
documentation on the basics. synthedit is a bit like
that, mostly finding out stuff by trying and asking
questions.

it’s been a long Ctrlr day..

[human fly]

update:
ok i just checked this with midiox, and it is working.
but it has to be in Panel Mode or (sysex/all?) output
is disabled.

it just has to have ‘xx’ for the variable, and ‘z5’ for
the checksum byte.

glad that it is simple! i knew it had to be hehe

[human fly]

little post script to this: initially had a bit of
a headscratch moment, because it wasn’t working again:
i had forgotten to set ‘MIDI message type’, it still
said ‘None’ – so you have to set that to ‘sysex’, of
course.

all working now !

i then had another little issue with one control that
was producing a sysex running status message instead:
?why? was that? i noticed its value range was -7<>+7,
and minus values don’t exist with MIDI, so i set it to
0-14 with centre detent 7 instead, and it started
working again. resolved, except it now displayed the
absolute MIDI values instead of the DISPLAYED value
range, and i want it to show the Display values, like
the other -/+ controls i have, that are working.

this, of course, is resolved under ‘Modulator’ with the
‘Expression to evaluate when calculating midi message
value from the modulator value’ entry:
it says ‘ModulatorValue’ and you change that to say:

‘Modulator value+7’, to add the necessary offset
(in the case of -7<>+7/0-14)

hehe, it only took a minuite or so to figure that out,
i’m getting better at this… :o)

[human fly]

JayVee z5 thing does not currently produce the correct checksum.

found a method in the JD800 panel. not checked, but worth a look.
lots of stuff in the Lua section.

D50 panel is sending the correct checksum, but it seems the panel
is private, can’t see what is going on.

here’s for the JD800 panel checksum:

function sendSysexModulatorValue(modulator, newValue)

local uid, val, add, lsb, chk, syx

uid = getModulatorUID(modulator)

if (uid <= 383) then add = math.floor(uid / 128) lsb = (uid % 128) val = newValue chk = (128 - ((add + lsb + val) % 128)) syx = string.format("f0 41 10 3d 12 00 %.2x %.2x %.2x %.2x f7", add, lsb, val, chk) panel:sendMidiMessageNow(CtrlrMidiMessage(syx)) else if (gPanelMode ~= cPanelModeToneXInit) then for i = 1, 4, 1 do if (gToneButtons[i + 4]:getModulatorValue() == 1) then uid = ((i - 1) * 72) + 96 + tonumber(modulator:getPropertyString("modulatorCustomIndex")) + 1 assignPatchModulatorValue(gPatchModulators[uid], newValue) end end end end end function setActiveTones(newValue) setCommandTones(newValue, 4) end

[human fly]

it doesn’t use the MIDI message type, it uses ‘Called when the
modulator value changes, and the Lua ?method? is called
metSendSysexModulatorChanged. it’s longer than what i showed above.

i can’t work out how the JayVee panel is providing a checksum
via the z5 signifier. have to check if it’s even sending the
correct checksum…(JD800 isn’t sending anything)
JayVee DOES send correct checksum. what am i missing?
am using this good little checksum calculator, just unzip,
no install:

http://www.bwalk.com.au/Convert/Convert.html

[human fly]

just guessing, but i reckon a good way would be a method
that specifies the number of bytes between F0 and F7,
identifying the address bytes (3) and values byte(1) to
be checksummed, and how, using a signifier LIKE ‘z5’ to be
the checksum byte, – KEEPING the MIDI message type category,
and using Modulator/CalledWhenModulatorValueChanges for the
Lua.

that is the most straightforward, in my limited capacity
to judge this. certainly most userfriendly. you can still
keep the easy sysex message entry box, copy and paste,
view it easily, etc. – it is reasonably logical for a first
time user to understand and bears some relation to the way
you do it on other platforms.

what would also be good, especially for multitimbral synths
such as this, would be to be able to specify basic MIDI
channel, so you’re not always stuck with using it on ie:
MIDI channel 1.

[human fly]

Possemo, check this out: z5 represents the number of
bytes in the address+value. jv1080 uses 5 bytes, the
D-110 uses 4, so z5 needs to be z4 in this case.
just going to try it now.

[human fly]

excellent – it’s correct now.

go on, just say it: rtfm 🙂
i had not looked at that before. it looks very
complete, i’ll have a proper read. it looks like
a good general reference.

“Checksums tN t=type N=num bytes to count
All checksums have the same format, tN, where the “t” token indicates the type of checksum to calculate, and N is a number that tells Ctrlr how many bytes to before the checksum byte to include in the checksum algorithm (a checksum is a number that verifies if the reception of data is correct, it needs some data to be calculated, so the N number tells Ctrlr how much data to read)

Roland JP8080 checksum, (zN for example z5)
Waldorf Rack Attack checksum (wN for example w5)
Ignore this byte on input, this is a special IGNORE token, that tells Ctrlr not to use this byte when comparing incoming MIDI data, it will considered always a “match”
”

[dnaldoog]

07/10/2018 Note: see the end of this post for a better formula. This formula returns an incorrect value for numbers adding up to over 256 (although maybe a sysex sent message never adds up to that much?)

The following function calculates and returns a Roland checksum. Pass parameters to it as in:
local cs=myCheckSum(0x06,0x30,0x00,0x4F,0x64) for example
cs = 23 (or 0x17)

myCheckSum=function(...)
    --1. Convert the hex values to decimal. (function parameters are automatically converted)
    --2. Add the values together, but if the answer to any sum exceeds 127 then subtract 128.
    --3. Subtract the final answer from 128.
    --4. Convert the resulting value back to hex and use as the checksum.
    local total=0
    local result=0
    for i,v in ipairs(arg) do
        total=total+v --add up all the numbers
        if(total > 127) then
            total=total - 128
        end
    end

    result=128-total
	if result== 128 then result = 0 end -- If the result is 128 then substitute a value of 0
    return tonumber(result,10)

end --function
---------------------------------------------------------

• This reply was modified 5 years, 2 months ago by dnaldoog. Reason: correction if result == 128 then return 0 as checksum
• This reply was modified 4 years, 8 months ago by dnaldoog. Reason: formula may return a wrong value for numbers over 256

[human fly]

thanks! will check that out, am going to need to
construct the sysex message at some point, instead of
using the built-in sysex message entry box.

[dnaldoog]

You’re welcome Human Fly! – took me a while to work out, so I thought I would pass it on. As you can see from the commented code, I too used that web page as a reference.

[dnaldoog]

Hi Human Fly!

human fly wrote:

If the sum of the values comes to 128 then I’m sure it is clear that
the checksum is 128! Look at the arithmetic:
x + y = 128 ( 128 > 127 so…)
128 – 128 = 0
128 – 0 = 128 (The checksum is 128)

I think this is actually incorrect. If the result = 128, the checksum should be 0.

There’s a good explanation here:
https://www.bome.com/forums/viewtopic.php?t=11986
in Lua, something like:

 
myCheckSum=function(...) -- Roland Checksum
local sum=0
local result=0
for _,v in ipairs(arg) do
sum=sum+v
end
--// calculate the remainder of sum/128
local remainder=sum % 0x80
--// subtract the remainder from 128
result=0x80 - remainder
if result==0x80 then result=0 end 
return result
end --function
---------------------------------------------------------

…or

myCheckSum=function(sum)
local result=bit.band(sum,0x7f)
if result * 1 ~=0 then
result= 0x80-result
end
return result 
end

[human fly]

hi dnaldoog !

i was quoting eddie lotter there 😉
will test your new method – have not been doing
much Ctrlr lately. stuck on latest projet (ran
out of ideas temporarily)

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