It can be useful to determine the MCU part number at runtime (especially if the same firmware runs on multiple versions of the same MCU with different flash, sram sizes, or pin counts).

C implementation: https://github.com/kiibohd/controller/blob/master/Lib/chip_version.h#L170

Should be similar to UART in the simplest implementation.

USART has some additional functionality (probably should only be implemented on an is needed basis):

• Hardware serial pins: SCK, RTS, CTS, DCD, DTR, DSR, RI
• RS485
• ISO7816 (Smart Cardsz)
• IrDA
• SPI Mode
• Loop back mode

This peripheral is useful for encrypting/decrypting using AES.

12-bit ADC with a 16-to-1 mux.

https://docs.rs/embedded-hal/0.2.4/embedded_hal/adc/index.html
https://github.com/atsamd-rs/atsamd/blob/master/hal/src/common/thumbv7em/adc.rs

Should support:

• Free running mode
• Single conversion
• Gain and Offset control
• Temperature sensor

Unclear

• How to setup ADC settings (especially if tuning is needed)
• PDC format (probably should have a separate issued with embedded-dma)
• Supporting differential mode

atsam4s_a, atsam4s_b

• 1 Timer Module (3 Channels)
• 16bit registers
  atsam4s_c
• 2 Timer Modules (2x3 Channels)
• 16bit registers
  atsam4e
• 3 Timer Modules (3x3 Channels)
• 32bit registers

Only basic timer functionality for now.
Out-of-scope features

• Wave mode
• Chaining timer channels
• External clock input

The PWM module on atsam4 is a bit confusing as it has High and Low output pins. I believe these are intentioned for motor controllers as they are inverted pairs.

Effectively there are 4 PWM channels for both atsam4e and atsam4s.

Clock configuration is also a bit confusing.
There are 4 channels, but only 2 fully customizable clocks (see CLKA and CLKB). These clocks can be used on multiple channels (as well as a bunch of peripheral clock divisions). See 39.6.1 (either atsam4s or atsam4e) for more details.

https://docs.rs/embedded-hal/0.2.4/embedded_hal/trait.Pwm.html
https://docs.rs/embedded-hal/0.2.4/embedded_hal/trait.PwmPin.html

This will likely be one of the more difficult modules to write.

Fortunately, we can use this to help a bit: https://github.com/mvirkkunen/usb-device

The atsamd USB port is quite a bit different than atsam4 unfortunately: https://github.com/atsamd-rs/atsamd/tree/master/hal/src/common/thumbv7em/usb

avr is a bit closer but still has difference (but unfortunately doesn't have a usb implementation yet in avr-hal).

USB support won't be needed by all clients of the HAL. Setting up USB (clocks, etc) should be behind a feature flag.

Look for BUGBUG in source.

Needed features:

• Master mode
• Slave mode
• 4 CS
• SPI Modes
• Fixed Peripheral Select Mode
• Variable Peripheral Select Mode

https://docs.rs/embedded-hal/0.2.4/embedded_hal/spi/index.html
https://docs.rs/embedded-hal/0.2.4/embedded_hal/blocking/spi/index.html

Should be similar to atsamd qspi (with only 2 data pins) https://github.com/atsamd-rs/atsamd/blob/master/hal/src/common/thumbv7em/qspi.rs

Later

• PDC
• DMAC
• Multiplexed CS (up to 15 total CS)

Should be fairly straight-forward. atsamd RTC Mode 2 looks similar to atsam4 RTC https://github.com/atsamd-rs/atsamd/blob/master/hal/src/common/rtc.rs

There aren't a lot of examples yet (other than simple ones like this: https://github.com/stm32-rs/stm32f4xx-hal/blob/master/src/dac.rs) for MCU DACs (probably because they aren't a super common hardware feature).

Ideally this should support PDC supplied data clocked in using a TC timer. Which should allow for things such as sounds for a speaker.

Should be similar to #18

Has the same functionality between atsam4s and atsam4e.

Has two different types of interrupts:

• RTTINC (Real-time Timer Increment)
• ALMS (Alarm)

RTTINC can only use SLCK and has a 16-bit prescaler available

ALMS can be set using the 1HZ or SLCK clocks and has a 32-bit counter. When using the SLCK, the 16-bit prescaler can also be used.

The advantage of this timer is that it can handle very long durations (2^32 or about 136 years). I'm interested in using this timer because it frees up TC channels on atsam4s_a and atsam4s_b which only have 3 TC channels.

atsamd Mode 0 looks similar to RTT with the 32-bit counter: https://github.com/atsamd-rs/atsamd/blob/master/hal/src/common/rtc.rs

While not necessary to run code, there are a number of useful features in the EEFC.

• Setting GPNVMx bits (bootloader or main flash on boot)
• Reading Unique Identifier
• Erase flash (all, plane, sector, page)
• Write flash
• Read/Write/Erase user signature
• Handle multiple flash controllers (EFC0 and EFC1 for dual bank MCUs)

Possibly useful

• Lock regions (usually these are set during programming)

Note: There are some oddities with EEFC_FCMD_EWP where not all pages can be automatically erased when writing. This usually has to do with the page size (can't seem to find the datasheet/reference that I saw). My note in the BOSSA commit: kiibohd/BOSSA@599fae1

At minimum we should implement I2C master (atsamd doesn't have an I2C slave implementation afaict).
https://github.com/atsamd-rs/atsamd/blob/master/hal/src/common/thumbv7em/sercom/v1/i2c.rs
https://docs.rs/embedded-hal/0.2.4/embedded_hal/blocking/i2c/index.html

Both atsam4s and atsam4e have two TWI modules.

Ideally with optional support for PDC, but this can get complicated as it's actually less efficient to use PDC for I2C when the transfer sizes are small. So it's probably best to ignore this for now.

The data sheet only document three 4S variants. The missing variants are the SAM4SDx.

We should probably use https://github.com/FluenTech/embedded-time instead of time.rs

atsamd has a similar issue open: atsamd-rs/atsamd#333

This may be easier to work on sooner rather than later. But it will affect any code re-use from atsamd.