ATmegaxxM1-C1: Arduino Core for ATmegaxxM1/C1 CPUs

Atmel offers a line of CPUs compatible with the CPUs commonly used in Arduino boards. Some have additional features, such as the ATmega32M1 which includes built in CAN (Control Area Network) hardware.

ATmegaxxM1-C1 is an extension to the Arduino IDE environment enabling several of these CAN containing CPUs.

• Currently supported CPUs include:
  • ATmega64M1
  • ATmega32M1
  • ATmega16M1

Future:

• Inclusion of ATmega32C1, ATmega64C1

Enhancements

The ATmegaxxM1/C1 CPUs have some additional features which have allowed for the API to be extended. Additions over the 'standard' Arduino are:

• Enhancement to ANALOG-READ() --> Additional ADC inputs

  • A9 will return the internal AVR temperature sensor. Caution: The ADC reference MUST first be set to 2.56v via: analogReference(INTERNAL);
  • A10 will return Vcc/4
  • ADO will return results of built in differential amp AMP0 using: (D9 - D8) * GAIN
  • AD1 will return results of built in differential amp AMP1 using: (A4 - A3) * GAIN
  • AD2 will return results of built in differential amp AMP2 using: (D10 - A6) * GAIN
  • analogRead() of Differential amps returns a SIGNED + or - (+511 .. - 511) value depending on the relative voltages of the +&- inputs.
  • When the internal differential amps have been enabled, the existing analog port can still be read individually, however the Digital ports are disables to reduce noise.

• Enhancement to PIN-MODE() --> Setting up of built in differential amps AMP0..AMP2

  • 1st parameter selected the differential amp to enable. Use: AD0, AD1, or AD2
  • 2nd parameter specific gain to use. Use: GAIN5, GAIN10, GAIN20, GAIN40
  • Example to use ADO (Ports D9 - D8): pinMode(AD0, GAIN20);
  • To disable a differential amp and restore ports to their original use, call pinMode() with the port you wish to use normally
  • Example to restore D9 (and D8), AD0 will be turned off: pinMode(D9, INPUT);

• Enhancement to ANALOG-WRITE() --> Access to DAC (Digital to Analog Converter)

  • A DAC is optional routed to port 10, use predefined DAC_PORT
  • writing an along value to DAC_PORT will cause the DAC to be enabled and the value used to create a analog voltage
  • DC is 10bits (just like the ADCs). Valid values are from 0..1023
  • the DAC uses the same reference as the ADCs. See analogReferance();
  • Example to set the DAC to 1/2 voltage: analogWrite(DAC_PORT, 512);

• Change in ANALOG-REFERENCE()

  • When called using INTERNAL, a 2.56v reference is selected vs. the 1.1v on the ATmega328p
  • This is due to the hardware.

• CAN - See: https://github.com/thomasonw/avr_can for Arduino compatible library

Summary of new Keywords: GAIN5, GAIN10, GAIN20, GAIN40, DAC_PORT

Notes

There are some small hardware differences between the ATmegaxxM1/C1 CPUs and the ATmega328 (used in the Uno). Mostly this will not be an issue, but one should be aware of them, including:

• The ATmegaxxM1/C1 CPUs only have two timers, TIMER0 and TIMER1. The function TONE uses the 'last timer', in this case TIMER1 (as opposed to TIMER2 in the ATmega328 / Uno)
• The internal reference voltage is 2.56v, as opposed to 1.1v

Special note concerning PSC ports at power-on. The ATmegaxxM1 CPUs contains a high speed PSC (Power Stage Controller) subsystem. Targeted for high-speed PWM, most commonly in a push-pull configuration. There are three channels for a total of 6 ports. A special feature of the ATmegaxxM1 CPU is the ability to hold those ports at a pre-determined value at initial power-on and/or reset, to prevent unintended actions until such time as the startup code is able to execute.

Fuse PSCRB has been set by default causing all 6 PSC ports to be held LOW until such time as when they are used or reconfigured to a different purpose. Care should be taken in hardware design NOT to tie these pins to a value other then GND. If there is a need to do so, make sure to use a current limiting resistor. The ports affected are: PB0, PB1, PB6, PB7, PC0, PD0 (Arduino ports: D5, D6, A7, A8, D12 & D11)

Though the ATmegaxxC1 does not contain a PSC subsystem, fuse PSCRB is still set - refer to Atmel users document to confirm the behavior of the ATmegaxxC1 CPU with this fuse set.

Port Mapping

Installation

This is designed for Arduino 1.6.7+

Option 1) Arduino Board Package Manager:

1. Start Arduino
2. Open menu File/Preferences
3. Click the 'window box' to the right of the 'Additional Boards manager URLs:' entry window.
   • This will allow you to add more than one entry
4. Copy the following URL into the box.
   • https://thomasonw.github.io/ATmegaxxM1-C1/package_thomasonw_ATmegaxxM1-C1_index.json
5. Press OK button to close the data entry window
6. Press OK button to close the Preferences menu.
7. Open the Tools/Boards menu and select Boards Manager
8. Scroll down and click on the 'ATmegaxxM1-C1 by thomasonw version x.x.x' entry
9. press the Install button

Option 2) Manual Install:

1. Copy down the ZIP file to your local computer.
2. Open the Zip File, and copy the entire content to your users local hardware subdirectory.
   • in Windows, this is: "Libraries/Documents/Arduno/Hardware"
3. Restart the Arduino IDE

After either is used to install the support files, you can select the new CPUs from the tools/boards menu.

Support for IDE versions released prior to 1.6.7 may be found at: http://smartmppt.blogspot.com/search/label/xxM1-IDE

Versions

v1.0.3 --> Original porting using rather old CORE files. Does NOT implement analogWrite() for DAC. analogRead() of differential ports are not corrected for +/- values (raw ADC count is returned)

v1.0.4 --> Reported to new CORE files from Arduino 1.6.8. Added DAC support. analogRead() of differential ports are not corrected for +/- values (raw ADC count is returned)

v1.0.5 --> pinMode(DAC_PORT,xxx) disconnects DAC from port (is connected by analogWrite(DAC_PORT, xx). analogRead() differential ports corrected for +/- values.

v1.0.6 --> Enabled TONE capability (note, interfers with PWM as it uses the same timer..), corrected SerialWrite IRQ race bug.

v1.0.7 --> Initialize VREF at 1st usage of DAC, restructured to Arduino menu selections, added menu options for PWM initial state (Thank you Geraldjust).

V1.0.8 --> Added support for dedicated 64m1 with Arduino footprint https://www.tindie.com/products/15615/ (By GeraldJust)

V1.0.9 --> Added support for ATmega16M1

CORE files

A major effort for this porting effort is the modification of the CORE include files used by Arduino. There is a separate GitHib repository which contains the edits I have made to enable the ATmegaM1/C1 CPUs: https://github.com/thomasonw/Arduino---CORE-files-for-ATmegaM1-C1-port/tree/master/hardware/arduino/avr/cores/arduino

It is forked from the master Arduino files to allow updating from them as well.