ATTiny co-processor on CM Panel POE

This article explains in detail the functions performed by the Microchip ATTiny88 co-processor present on the CM-Panel POE

Microchip ATTiny88 in an AVR RISC-based CMOS 8-bit microcontroller with:

8 KB ISP Flash memory
6 4B EEPROM
512B SRAM
28 general purpose I/O lines

More info are available on the Microchip ATTiny88 page at https://www.microchip.com/en-us/product/attiny88.

This processor is programmed in-factory to perform the following functions:

Measure each 1s the on-board voltages and display a report on the serial debug port
Manage the correct shutdown in case of power failure to avoid the microSD curruption
Indicate the state of charge of the supercap using the RGB led
Manage the state of display power supply circuits
Send a signal via a GPIO line to shutdown Linux

The firmware used is this:

pwr.ino

This article explains how to compile it and flash the ATTiny with your own version.

Signals wired to the co-processor

These are the GPIO lines used by the ATTiny and their respective purposes:

PIN	DIR	NAME	USE	ACTIVE	CMx GPIO
PA0	ADC	MeasBacklit
PA1	ADC	MeasVSC
PA2		Main5V
PA3		Flag4
PB0		Flag1	N.C.
PB1		Flag2	N.C.
PB2		Flag3	N.C.
PB3		MOSI
PB4		MISO
PB5		SCK
PB6	OUT	Disp On	Display ON	High	27
PB7	OUT	KB	RGB led blue	Low
PC0	ADC	Meas1V8
PC1	ADC	Meas3V3
PC2	ADC	Meas5VExt
PC3	ADC	Meas5VInt
PC4		micro_SDA
PC5		micro_SCL
PC6		NRST
PC7	IN	Touch_INT		Low
PD0	OUT	GOSHDN	Shutdown command to CMx module	Low	25
PD1	IN	SHDNDONE	Shutdown done by CMx module	High	26
PD2	IN	INT1#	Interrupt from RTC	Low
PD3	IN	Pushbutton	P2 Button (Start/stop)	Low
PD4	OUT	KG	RGB led green	Low
PD5	OUT	KR	RGB led red	Low
PD6	OUT	Txdata	Debug port TX
PD7	IN	Rxdata	Debug port RX

Install the Arduino IDE to program the ATTiny88 co-processor

Download and install the Arduino IDE from the official Arduino website. We used Legacy IDE 1.8.19 to write this article.

https://www.arduino.cc/en/software

add the ATtiny support to the Arduino IDE ny navigating to Arduino > Preferences... > Additional Board Manager URLs: and add the following URL for the ATtiny core by Spence Konde (DrAzzy):

http://drazzy.com/package_drazzy.com_index.json

Click "OK" to close the Preferences window.

Open the Board Manager by navigating to Tools > Board > Boards Manager....

In the Boards Manager window search for ATtiny and select ATTinyCode by Spence Konde then press then .

Now navigate to Tools > Boards > ATTinyCore > ATtiny48/88 (Optiboot)

Configure the processor settings

Tools > Chip > ATTiny88
Tools > Clock Source > 4MHz (Internal)

Copy inside the editor this sketch:

pwr.ino

then select the menu Sketch > Verify/Compile

Sketch uses 4342 bytes (53%) of program storage space. Maximum is 8192 bytes.
Global variables use 292 bytes (57%) of dynamic memory, leaving 220 bytes for local variables. Maximum is 512 bytes.

then Sketch > Export compiled Binary.

then Sketch > Show sketch folder and check that the file pwr.ino.hex exist.

If you have a Tiny USB programmer you code inject the code directly by hardware to the co-processor using the J4 Prog port on CM-Panel POE.

If not transfer the file pwr.ino.hex to the CM-Panel POE microSH using SSH and program the co-processor using avrdude.

How to inject the code inside the ATTiny88 co-processor

There are some ways to transfer the binary code inside the ATTiny flash memory:

Using the Tiny USB cheap ISP programmer and Arduino IDE
Using the Tiny USB cheap ISP programmer and the CM-Panel itself
Using an USB to serial converter and the Arduino IDE
Using an USB to serial converter and the CM-Panel itself

Methods 3 and 4 are possible because the ATTiny become already programmed with the ATTiny firmware + Optiboot loader
Methods 1 and 2 works also with a fully blank ATTiny

In case of ISP using the CM-Panel itself install avrdude by typing:

$ sudo apt update
$ sudo apt install avrdude

Download the avrdude configuration file from our site by typing:

$ wget https://www.acmesystems.it/www/cmpanel-poe_attiny/avrdude.conf

Download the ATTiny firmware from our site by typing:

$ wget https://www.acmesystems.it/www/cmpanel-poe_attiny/pwr.ino.hex

Insert the Tiny USB programmer between one of the USB port of CM-Panel and the J4 PROG port and type:

$ sudo avrdude -Cavrdude.conf -v -pattiny88 -cusbtiny -e -Uefuse:w:0xfe:m -Uhfuse:w:0b11010111:m -Ulfuse:w:0xE2:m -Uflash:w:pwr.ino.hex:i

or insert an USB to serial adapted between an USB port on CM-Panel POE and the ATTiny debug port available on EXP2 header, open the PROG BYPASS jumper, then type:

$ sudo avrdude -Cavrdude.conf -v -pattiny88 -carduino -P/dev/ttyUSB0 -b19200 -D -Uflash:w:pwr.ino.hex:i

and reset the ATTiny by pressing the reset button near the supercap (Jumpers, headers and push buttons on CM-Panel POE).

ATTiny debug port

The coprocessor has a debug serial port whose signals are exposed on the EXP2 connector as shown in the figure.
These signals are at 3.3 volts with the following serial parameters: 19200 baud,N,8,1 no flow control.

Notes

Get the stand alone optiboot binary file:

$ wget https://www.acmesystems.it/www/cmpanel-poe_attiny/optiboot_attiny88_8000000L.hex

Programming just the Optiboot bootloader width Atmel ICE

$ sudo avrdude -Cavrdude.conf -v -pattiny88 -catmelice_isp -Pusb -e -Uefuse:w:0xfe:m -Uhfuse:w:0b11010111:m -Ulfuse:w:0xE2:m -Uflash:w:optiboot_attiny88_8000000L.hex:i

Programming just the bootloader with USBTiny

$ sudo avrdude -Cavrdude.conf -v -pattiny88 -cusbtiny -e -Uefuse:w:0xfe:m -Uhfuse:w:0b11010111:m -Ulfuse:w:0xE2:m -Uflash:w:optiboot_attiny88_8000000L.hex:i