Feature highlights

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Initially, I wanted to build a split board. However, since I already have a split (crkbd), making a Arteus/Reviuge-like board makes more sense.

The design is using aggressive stagger (same column stagger like my split design), and 15 degree angle of columns.

Other features:

• OLED status display
• RGB underglow
• Audio
• Encoder

Design considerations for STM32

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I’ll be using F411 due to lack of F072 stock.

Tips for setup a stm chip in qmk: https://discord.com/channels/440868230475677696/440870965728116754/839978277489082370

Snippet to find keyboards that uses a certain chip:

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 % git grep 'MCU\s*=\s*STM32F411' keyboards/
 keyboards/handwired/onekey/blackpill_f411/rules.mk:MCU = STM32F411
 keyboards/handwired/onekey/blackpill_f411_tinyuf2/rules.mk:MCU = STM32F411
 keyboards/handwired/pill60/blackpill_f411/rules.mk:MCU = STM32F411
 keyboards/handwired/riblee_f411/rules.mk:MCU = STM32F411
 keyboards/matrix/m20add/rules.mk:MCU = STM32F411
 keyboards/matrix/noah/rules.mk:MCU = STM32F411
 keyboards/tkw/grandiceps/rules.mk:MCU = STM32F411
 keyboards/tkw/stoutgat/v2/f411/rules.mk:MCU = STM32F411
 keyboards/zvecr/zv48/f411/rules.mk:MCU = STM32F411

DMA channels for peripherals

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Peripherals like I2C, SPI and ADC, DAC uses DMA channels. PWM also can use DMA for better performance, for example, for LED dreivers. STM32F072 has 7 DMA channels(details can be found in reference doc). When choosing peripherals, we need to choose carefully so that DMA channels won’t collide.

QMK uses DMA for the following:

• WS2812 LED: pwm driver uses DMA+PWM.
• Audio: DAC driver uses DMA. PWM driver doesn’t use DMA.
• OLED: Uses I2C which uses DMA channels.

F072 DMA details

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F072 only has one DMA controller(DMA1), which has 1 channel, with 7 streams.

• I2C1: uses DMA streams 6/7(or 2/3). (Requires magic boot code to configure.)
• DAC1/2: uses DMA streams 3 and 4.
• SPI1: streams 2/3.
• SPI2: streams 4/5 or 6/7.
• TIM3_CH1: stream 4
• TIM1_CH1: stream 2

F411 DMA details

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F411 has 2 DMA controllers, each has 8 channels and each channel with 8 streams.

Summary of DMA usage in my design:

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Audio Driver

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Two options: DAC and PWM. DAC would occupy one or two DMA channels. PWM doesn’t use DMA.

Audio with DAC

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Using two pins can provides higher voltage amplitude and louder volume.

• Pins(A4/A5). ref, ref2

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// Audio configuration
#define AUDIO_PIN A4
#define AUDIO_PIN_ALT A5
#define AUDIO_PIN_ALT_AS_NEGATIVE
#define A4_AUDIO
#ifndef STARTUP_SONG
#    define STARTUP_SONG SONG(STARTUP_SOUND)
#endif  // STARTUP_SONG

Audio with PWM

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• Use any timer’s PWM to output square wave. This only support single pin mode.

We use TIM3_CH1 as example. (use tim6 for audio state timer)

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//halconf.h:
#define HAL_USE_PWM                 TRUE
#define HAL_USE_PAL                 TRUE
#define HAL_USE_GPT                 TRUE
#include_next <halconf.h>

// mcuconf.h:
#include_next <mcuconf.h>
#undef STM32_PWM_USE_TIM1
#define STM32_PWM_USE_TIM1                  TRUE
#undef STM32_GPT_USE_TIM6
#define STM32_GPT_USE_TIM6                  TRUE

//config.h:
// Use pin C6(TIM3_CH1) PWM
#define AUDIO_PIN A8
#define AUDIO_PWM_PAL_MODE 1
#define AUDIO_PWM_DRIVER PWMD1
#define AUDIO_PWM_CHANNEL 1
#define AUDIO_STATE_TIMER GPTD6

OLED

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I2C: Use I2C1(pins B6/7). ref

Note that, pull up resistors(4.7kOhm) are needed for I2C pins.

Magic fix

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For F072, extra configuration is needed to use I2C1 correctly. For details, see discord, discord2

Example code

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// example config: https://github.com/qmk/qmk_firmware/blob/master/keyboards/xelus/kangaroo/config.h
//set I2C1_SCL_PAL_MODE and I2C1_SDA_PAL_MODE to 1. (PINs B6/7)

#define I2C1_TIMINGR_SCLDEL 3U
#define I2C1_TIMINGR_SDADEL 1U
#define I2C1_TIMINGR_SCLH     3U
#define I2C1_TIMINGR_SCLL   9U

//Copy board_init() from https://github.com/qmk/qmk_firmware/blob/master/keyboards/xelus/kangaroo/kangaroo.c :

void board_init(void) {
  SYSCFG->CFGR1 |= SYSCFG_CFGR1_I2C1_DMA_RMP;
  SYSCFG->CFGR1 &= ~(SYSCFG_CFGR1_SPI2_DMA_RMP);
}

//The problem is that platforms/chibios/GENERIC_STM32_F072XB/configs/mcuconf.h contains:
#define STM32_I2C_I2C1_RX_DMA_STREAM STM32_DMA_STREAM_ID(1, 7)
#define STM32_I2C_I2C1_TX_DMA_STREAM STM32_DMA_STREAM_ID(1, 6)

//But this is actually an alternate configuration for I2C1 DMA streams, and it needs to be enabled by setting the SYSCFG_CFGR1_I2C1_DMA_RMP bit.

//The SYSCFG_CFGR1_SPI2_DMA_RMP clearing part might not actually be needed (the power-on state for this bit should be 0), but you can include it just to be sure.

Backlight RGB:

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• LED: use WS2812S

RGB driver using PWM

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Uses PWM and DMA. Here I’m using TIM3_CH4 on pin B1 as output, and connect it with pull up resistor to 5V. (B1 is a 5v tolerant pin)

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// rules.mk
RGBLIGHT_DRIVER = WS2812
// config.h
#define RGB_DI_PIN B1
#define WS2812_PWM_DRIVER PWMD3
#define WS2812_PWM_CHANNEL 4
#define WS2812_EXTERNAL_PULLUP
// Set B1 to tim3 ch4
#define WS2812_PWM_PAL_MODE 2
// DMA request mapped on this DMA channel only if the corresponding remapping
// bit is cleared in the SYSCFG_CFGR1 register. For more details, please refer
// to Section 9.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1) on page165.
#define WS2812_DMA_STREAM STM32_DMA1_STREAM2
#define WS2812_DMA_CHANNEL 5

If using pin B15(tim15) (F072)

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// rules.mk
RGBLIGHT_DRIVER = WS2812
// config.h
#define RGB_DI_PIN B15
#define WS2812_EXTERNAL_PULLUP
// using TIM15 channel 2
#define WS2812_PWM_DRIVER PWMD15
#define WS2812_PWM_CHANNEL 2
// Set B15 to tim15 ch2
#define WS2812_PWM_PAL_MODE 1
// DMA setup needs to be verified.
#define WS2812_DMA_STREAM STM32_DMA1_STREAM5
//mcuconf.h if using tim15
//#define STM32_TIM15_SUPPRESS_ISR

RGB driver SPI

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Use SPI2(B15). ref spi. This requires other spi pins unused.(miso and sck, e.g. B13 and B14)

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#define WS2812_SPI SPID2
// Pins 15/14/13
#define WS2812_SPI_MOSI_PAL_MODE 0
#define WS2812_SPI_MOSO_PAL_MODE 0
#define WS2812_SPI_SCK_PAL_MODE 0

Note: Extra setup is needed for F072 B15 pin. details

The fix is to define #define WS2812_SPI_USE_CIRCULAR_BUFFER. The flag is only available in develop branch. Anoth

Component choices

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Use this site to search JLCPCB parts for SMD assembly service availability and price.

Summary:

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MCU

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I’m using STM32 MCU, which is more powerful than the atmega on pro micros. The atmega32u4 is 8 bit processor and only has 32K memory size. In comparison, the Arm chips are 32bit, and has more program memory(F072C8 has 64K, F072CB has 128K, F411 has 256K/521K flash and 128K SRAM).

Initially I wanted to use STM32F072CBU6, which is also used in Ferris. However, it became OOS and I had to pick another chip. I found STM32F411 whixh id more powerful.

One caveat is that F4 series doesn’t have built-in eeprom emulator. An external eeprom chip is needed, otherwise some features are not usable, like bootmagic, on-board settings(default layers, for example).

Reset button circuit

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To reset(and enter bootloader), we need to trigger both NRST and BOOT0 pins. This guide suggested 3 variants and I’m using the middle one for simplicity. For this circuit, we need a transistor. I’m not using the prebiased one shown there (50V, 100mA, 2.2kOhm and 47kOhm) since it’s extended part and has $3 extra charge. Instead I’m using a 40V, 200mA NPN transistor and adding external resistors.

Fuse

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Ferris used “Polymeric 15V 1A 100ms 750mΩ 1206 PTC Resettable Fuses RoHS”, however the model is OOS, so I searched on LCSC and found C369167 which has similar spec. For the diode, Ferris used C435473, and I’m using the same.

Schottky Diode

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Ferris used RB060MM-30, which is 30V vr, 490mV vf. I use SS14 which is basic part in JLCPCB. It is “40V 1A 550mV @ 1A” which is pretty close.

Resistors and capacitors

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I’m using all 0603 footprint.

TODO

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Some changes to apply to next design:

• Add 4.7k pull up to i2c pins.
• Use 8Mhz crystal instead of 25MHz. ref