Experiment with i2c Multibus and SSD1306 OLED

Insanity · Joined: 25 Apr 2021 Posts: 8

Hello,
I'm not getting any further at the moment.
I am trying to operate several OLEDs on an Atmega 328p.
It works individually with the normal i2c declaration.
Individually with i2c Multibus, no reaction from the display.

The normal declaration with Config SDA = always works, but only one bus.
But I need 3 buses.
and the declaration with
Config I2cbus = 0, Scl = PortD.6, Sda = PortD.5
i2cbus = 0
it does not work.
The program always remains
Config Graphlcd = Custom, Cols = 128, Rows = 64, Lcdname = "SSD1306"
hang.

' Insanity
' Versuch mit i2c Multibus und OLED

$Regfile="M328pdef.dat"
$Crystal=8000000
$hwstack=64
$swstack=64
$framesize=64

'Display Config
$lib "glcdSSD1306-I2C.lib"
Config Graphlcd = Custom , Cols = 128 , Rows = 64 , Lcdname = "SSD1306"
Config I2CDelay = 5

Config I2cbus = 5 , Scl = PortD.6 , Sda = Portd.5
i2cbus=5

'Config Scl=PORTD.6
'Config Sda=PORTD.5

I2cInit
waitms 60

cls
Setfont My6_8
Lcdat 1 , 1 , "Test 1"
Lcdat 2 , 1 , "Test 2"
Lcdat 3 , 1 , "Test 3"
Lcdat 4 , 1 , "Test 4"
Lcdat 5 , 1 , "Test 5"
Lcdat 6 , 1 , "Test 6"
Lcdat 7 , 1 , "Test 7"
Lcdat 8 , 1 , "Test 8"

Do
Loop
End
$include "My6_8.font"

Is there a solution for the problem?

(BASCOM-AVR version : 2.0.8.3 )

enniom · Joined: 20 Oct 2009 Posts: 537

I2C address or CS (chip select)?

E

Insanity · Joined: 25 Apr 2021 Posts: 8

I do not understand your question

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

with i2c a device often can have multiple addresses. in that case you can use one bus and use different addresses to address the device.
but in case of an lcd it often has a fixed address. so one solution is to use the multibus option.

but there is also to point of the driver. in this case there is no provision to use it multiple times.
but it is simple :

use the multibus to set up 3 buses.
for each connected device, use INITLCD when the bus is selected.
this will initialize the lcd.

Insanity · Joined: 25 Apr 2021 Posts: 8

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

the lcd lib was not written with multiple lcd in mind so it might need some changes.
your code looks good.
Also, for lcd speed is an issue so i assume that the hardware i2c is used.

i had a quick peek and the problem seems to be that the Z pointer is used by both the graphical lib and the multibus lib.
when you have a look inside the lcd lib you find and the begin:

[_GLCD]
$EXTERNAL _LPMBYTE, _GLOCATE
_Init_lcd:
_LCD_INIT:
_SET_DISPLAY:
#IF _XMEGA
rcall _XM_i2c_start ; send start to access the bus
#ELSE
call _i2c_start ; send start to access the bus
#ENDIF

this was to make the lib work for XMega. And xmega also uses Z pointer.

under the data table you find this code which is only for xmega:

#IF _XMEGA
_XM_i2c_start:
push r24
push r25
push r30
push r31
loadadr TWIC_CTRL,Z
ldi r25,1 ; TWIC
call _i2c_start
rjmp _xmi2c_exit

_XM_i2c_write:
push r24
push r25
push r30
push r31
loadadr TWIC_CTRL,Z
ldi r25,1 ; TWIC
call _i2c_write ; write data in r17
rjmp _xmi2c_exit

_xm_i2c_stop:
push r24
push r25
push r30
push r31
loadadr TWIC_CTRL,Z
ldi r25,1 ; TWIC
call _i2c_stop
; no code here !!

_xmi2c_exit:
pop r31
pop r30
pop r25
pop r24
Ret
#ENDIF

here you see that registers are saved, then function is called , and the regs are restored.
A similar construction is needed.
#IF _USE_MULTIBUS
_XMulti_i2c_start:
push r24
push r25
push r30
push r31
;;;;;; loadadr TWIC_CTRL,Z this can be removed
;;;;;;; ldi r25,1 ; TWIC this can be removed
call _i2c_start
rjmp _xmultii2c_exit

etc.
#ENDIF

and the other code :
#IF _XMEGA
rcall _XM_i2c_start ; send start to access the bus
#ELSE
call _i2c_start ; send start to access the bus
#ENDIF

would become:

#IF _XMEGA
rcall _XM_i2c_start ; send start to access the bus
#ELSEIF _USE_MULTIBUS
call _XMulti_i2c_start ; send start
#ELSE
call _i2c_start ; send start to access the bus
#ENDIF

when you add the rest in a similar way it should work.

a simpler way would be when you can alter the lcd hardware address.
that way they can be on the same bus and then the changes to the lib would be minimal.

O-Family · Joined: 23 May 2010 Posts: 320 Location: Japan

Since "i2c-multibus.lib" uses many registers other than the Z pointer (R30, R31), many libraries that control the LCD with I2C will not work.

This countermeasure requires an improvement to save many registers in each LCD library.

Therefore, I think it is better to save the register used by "i2c-multibus.lib".

Insanity · Joined: 25 Apr 2021 Posts: 8

I changed the lib as suggested.
The program remains at the config Graphlcd = Custom, Cols = 128, Rows = 64, Lcdname = "SSD1306"
Hang line.

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

that is an option too. but under normal conditions there is no need for the multibus lib to save registers. the whole idea of all high level commands is that they may trash all registers.
only when you call high level statements from inside asm you get this problem.
so under normal conditions it is a waste of code.
I always prefer to change the lib that requires the save/restore.

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

ok, well done.
there seem to be some more regs that need to be saved.
For the init procedrue this is R21

this code ;

ldi r21,26 ; 26 bytes
_lcd_init_lp:
call _lpmbyte ; get double command first byte
mov r17,r0

#IF _XMEGA
rcall _xm_i2c_write ; write
#ELSEIF _USE_MULTIBUS
PUSH R21
rcall _xMulti_i2c_write ; write
POP R21
#ELSE
call _i2c_write ; write
#ENDIF

dec r21
brne _Lcd_init_lp

would fix it. See the bold part

Insanity · Joined: 25 Apr 2021 Posts: 8

A small success!
The display shows something.
They are just confused signs and they keep going through.
even if nothing is written.
Assembler is not my world.
Laughing

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

ok, that means the init works.
i will check the rest.

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

ok, since the following registers are used by the i2c driver they need to be saved as well :

R20
R21
R22
R23

so when you save/restore these, it should work.

Insanity · Joined: 25 Apr 2021 Posts: 8

Mark, thank you very much.
It runs. Test with 2 displays. Super