`bitbangio` – Digital protocols implemented by the CPU

The bitbangio module contains classes to provide digital bus protocol support regardless of whether the underlying hardware exists to use the protocol.

First try to use busio module instead which may utilize peripheral hardware to implement the protocols. Native implementations will be faster than bitbanged versions and have more capabilities.

All classes change hardware state and should be deinitialized when they are no longer needed if the program continues after use. To do so, either call deinit() or use a context manager. See Lifetime and ContextManagers for more info.

For example:

import bitbangio
from board import *

i2c = bitbangio.I2C(SCL, SDA)
print(i2c.scan())
i2c.deinit()

This example will initialize the the device, run scan() and then deinit() the hardware. The last step is optional because CircuitPython automatically resets hardware after a program finishes.

Available on these boards

01Space 0.42 OLED ESP32C3
0xCB Helios
42. Keebs Frood
8086 USB Interposer
AITHinker ESP32-C3S_Kit
AITHinker ESP32-C3S_Kit_2M
ARAMCON Badge 2019
ARAMCON2 Badge
ATMegaZero ESP32-S2
Adafruit CLUE nRF52840 Express
Adafruit Camera
Adafruit Circuit Playground Bluefruit
Adafruit Circuit Playground Express 4-H
Adafruit CircuitPlayground Express
Adafruit EdgeBadge
Adafruit Feather Bluefruit Sense
Adafruit Feather ESP32 V2
Adafruit Feather ESP32-C6 4MB Flash No PSRAM
Adafruit Feather ESP32-S2 Reverse TFT
Adafruit Feather ESP32-S2 TFT
Adafruit Feather ESP32-S3 Reverse TFT
Adafruit Feather ESP32-S3 TFT
Adafruit Feather ESP32S2
Adafruit Feather ESP32S3 4MB Flash 2MB PSRAM
Adafruit Feather ESP32S3 No PSRAM
Adafruit Feather HUZZAH32
Adafruit Feather M4 CAN
Adafruit Feather M4 Express
Adafruit Feather MIMXRT1011
Adafruit Feather RP2040
Adafruit Feather RP2040 Adalogger
Adafruit Feather RP2040 CAN
Adafruit Feather RP2040 DVI
Adafruit Feather RP2040 Prop-Maker
Adafruit Feather RP2040 RFM
Adafruit Feather RP2040 Scorpio
Adafruit Feather RP2040 ThinkInk
Adafruit Feather RP2040 USB Host
Adafruit Feather RP2350
Adafruit Feather STM32F405 Express
Adafruit Feather nRF52840 Express
Adafruit Floppsy RP2040
Adafruit FunHouse
Adafruit Grand Central M4 Express
Adafruit HUZZAH32 Breakout
Adafruit Hallowing M4 Express
Adafruit ItsyBitsy ESP32
Adafruit ItsyBitsy M4 Express
Adafruit ItsyBitsy RP2040
Adafruit ItsyBitsy nRF52840 Express
Adafruit KB2040
Adafruit LED Glasses Driver nRF52840
Adafruit Macropad RP2040
Adafruit MagTag
Adafruit Matrix Portal M4
Adafruit MatrixPortal S3
Adafruit Metro ESP32S2
Adafruit Metro ESP32S3
Adafruit Metro M4 Airlift Lite
Adafruit Metro M4 Express
Adafruit Metro RP2040
Adafruit Metro RP2350
Adafruit Metro nRF52840 Express
Adafruit Monster M4SK
Adafruit PyGamer
Adafruit PyPortal
Adafruit PyPortal Pynt
Adafruit PyPortal Titano
Adafruit Pybadge
Adafruit QT Py ESP32 PICO
Adafruit QT Py ESP32-S3 4MB Flash 2MB PSRAM
Adafruit QT Py ESP32-S3 no psram
Adafruit QT Py ESP32C3
Adafruit QT Py ESP32S2
Adafruit QT Py RP2040
Adafruit QT2040 Trinkey
Adafruit Trellis M4 Express
Adafruit Vindie S2
Adafruit-Qualia-S3-RGB666
Ai Thinker ESP32-CAM
AloriumTech Evo M51
Archi RP2040
Arduino Nano 33 BLE
Arduino Nano 33 BLE Rev2
Arduino Nano ESP32
Arduino Nano RP2040 Connect
Artisense Reference Design RD00
AtelierDuMaker nRF52840 Breakout
AutosportLabs-ESP32-CAN-X2
BARDUINO 4.0.2
BBQ20KBD
BDMICRO VINA-D51
BLE-SS dev board Multi Sensor
BLING!
BLOK
BPI-Bit-S2
BPI-Leaf-S3
BPI-PicoW-S3
BastBLE
BastWiFi
Bee-Data-Logger
Bee-Motion-S3
Bee-S3
BlizzardS3
BlueMicro840
Bradán Lane STUDIO Explorer Badge
COSMO-Pico
CP32-M4
CRCibernetica IdeaBoard
Challenger NB RP2040 WiFi
Challenger RP2040 LTE
Challenger RP2040 LoRa
Challenger RP2040 SD/RTC
Challenger RP2040 SubGHz
Challenger RP2040 WiFi
Challenger RP2040 WiFi/BLE
Challenger+ RP2350 BConnect
Challenger+ RP2350 WiFi6/BLE5
Circuit Playground Express Digi-Key PyCon 2019
CircuitART Zero S3
CircuitBrains Deluxe
ColumbiaDSL-Sensor-Board-V1
CrumpS2
Cytron EDU PICO W
Cytron IRIV IO Controller
Cytron MOTION 2350 Pro
Cytron Maker Feather AIoT S3
Cytron Maker Nano RP2040
Cytron Maker Pi RP2040
Cytron Maker Uno RP2040
DFRobot Beetle ESP32-C3
DFRobot FireBeetle 2 ESP32-S3
Datanoise PicoADK
Datanoise PicoADK V2
Deneyap Kart
Deneyap Kart 1A
Deneyap Kart 1A v2
Deneyap Kart G
Deneyap Mini
Deneyap Mini v2
Diodes Delight Piunora
DynOSSAT-EDU-OBC
E-Fidget
ELECFREAKS PICO:ED
ES3ink
ESP 12k NodeMCU
ESP32 Devkit V1
ESP32-C3-DevKitM-1
ESP32-C6-DevKitC-1-N8
ESP32-C6-DevKitM-1
ESP32-H2-DevKitM-1
ESP32-P4-Function-EV
ESP32-S2-DevKitC-1-N4
ESP32-S2-DevKitC-1-N4R2
ESP32-S2-DevKitC-1-N8R2
ESP32-S3-Box-2.5
ESP32-S3-Box-Lite
ESP32-S3-DevKitC-1-N16
ESP32-S3-DevKitC-1-N32R8
ESP32-S3-DevKitC-1-N8
ESP32-S3-DevKitC-1-N8R2
ESP32-S3-DevKitC-1-N8R8
ESP32-S3-DevKitC-1-N8R8-with-HACKTABLET
ESP32-S3-DevKitM-1-N8
ESP32-S3-EYE
ESP32-S3-USB-OTG-N8
ESP8684-DevKitC-02-N4
Electrolama minik
Electronut Labs Blip
Electronut Labs Papyr
EncoderPad RP2040
Espressif ESP32 DevKitc V4 WROOM-32E
Espressif ESP32 DevKitc V4 WROVER
Espressif ESP32 TTGO T8 v1.7
Espressif ESP32-EYE
Espressif ESP32-LyraT
Espressif-ESP32-S3-LCD-EV-Board
Espressif-ESP32-S3-LCD-EV-Board_v1.5
Espruino Bangle.js 2
Espruino Pico
Espruino Wifi
Feather MIMXRT1011
Feather MIMXRT1062
FeatherS2
FeatherS2 Neo
FeatherS2 PreRelease
FeatherS3
FeatherS3 Neo
Fig Pi
Flipper Zero Wi-Fi Dev
Franzininho WIFI w/Wroom
Franzininho WIFI w/Wrover
Freenove ESP32-WROVER-DEV-CAM
Gravitech Cucumber M
Gravitech Cucumber MS
Gravitech Cucumber R
Gravitech Cucumber RS
HEIA-FR Picomo V2
HMI-DevKit-1.1
Hack Club Sprig
Hardkernel Odroid Go
Heltec ESP32-S3-WIFI-LoRa-V3
HexKyS2
HiiBot BlueFi
IMXRT1010-EVK
IMXRT1015-EVK
IkigaiSense Vita nRF52840
IoTs2
Kaluga 1
LILYGO T-DECK
LILYGO T-DISPLAY
LILYGO T-DISPLAY S3 v1.2
LILYGO T-Display S3 Pro
LILYGO T-Watch-S3
LILYGO TEMBED ESP32S3
LILYGO TTGO T-01C3
LILYGO TTGO T-DISPLAY v1.1
LILYGO TTGO T-DISPLAY v1.1 4M
LILYGO TTGO T-OI PLUS
LILYGO TTGO T8 ESP32-S2
LILYGO TTGO T8 ESP32-S2 w/Display
LOLIN S3 16MB Flash 8MB PSRAM
LOLIN S3 MINI 4MB Flash 2MB PSRAM
LOLIN S3 PRO 16MB Flash 8MB PSRAM
Lilygo T-watch 2020 V3
Luatos Core-ESP32C3
M5STACK STAMP-C3
M5Stack Atom Echo
M5Stack Atom Lite
M5Stack Atom Matrix
M5Stack Atom U
M5Stack AtomS3
M5Stack AtomS3 Lite
M5Stack AtomS3U
M5Stack Cardputer
M5Stack Core Basic
M5Stack Core Fire
M5Stack Core2
M5Stack CoreS3
M5Stack Dial
M5Stack M5Paper
M5Stack Stick C
M5Stack Stick C Plus
M5Stack Timer Camera X
MDBT50Q-DB-40
MDBT50Q-RX Dongle
MEOWBIT
MORPHEANS MorphESP-240
MagiClick S3 N4R2
Maker Go ESP32C3 Supermini
Maker Go ESP32C6 Supermini
Maker badge by Czech maker
MakerDiary nRF52840 MDK
MakerDiary nRF52840 MDK USB Dongle
MakerFabs-ESP32-S3-Parallel-TFT-With-Touch-7inch
Makerdiary M60 Keyboard
Makerdiary Pitaya Go
Makerdiary nRF52840 Connect Kit
Makerdiary nRF52840 M.2 Developer Kit
Maple Computing Elite-Pi
Melopero Shake RP2040
Metro MIMXRT1011
MicroDev microC3
MicroDev microS2
Mini SAM M4
MixGo CE
NUCLEO STM32F746
NUCLEO STM32F767
NUCLEO STM32H743
NanoS3
Neuron
NodeMcu-ESP32-C2
OMGS3
OPENMV-H7 R1
Oak Dev Tech BREAD2040
Oak Dev Tech Cast-Away RP2040
Oak Dev Tech PixelWing ESP32S2
Oak Dev Tech RPGA Feather
Open Hardware Summit 2020 Badge
Oxocard Artwork
Oxocard Connect
Oxocard Galaxy
Oxocard Science
P1AM-200
PCA10056 nRF52840-DK
PCA10059 nRF52840 Dongle
PYB LR Nano V2
Pajenicko PicoPad
Particle Argon
Particle Boron
Particle Xenon
PillBug
Pimoroni Badger 2040
Pimoroni Badger 2040 W
Pimoroni Inky Frame 5.7
Pimoroni Inky Frame 7.3
Pimoroni Interstate 75
Pimoroni Keybow 2040
Pimoroni Motor 2040
Pimoroni PGA2040
Pimoroni PGA2350
Pimoroni Pico DV Base W
Pimoroni Pico LiPo (16MB)
Pimoroni Pico LiPo (4MB)
Pimoroni Pico Plus 2
Pimoroni Pico dv Base
Pimoroni PicoSystem
Pimoroni Plasma 2040
Pimoroni Plasma 2040W
Pimoroni Plasma 2350
Pimoroni Servo 2040
Pimoroni Tiny 2040 (2MB)
Pimoroni Tiny 2040 (8MB)
Pimoroni Tiny 2350
Pimoroni Tiny FX
ProS3
PyCubedv04
PyCubedv04-MRAM
PyCubedv05
PyCubedv05-MRAM
PyKey 18 Numpad
PyKey 44 Ergo
PyKey 60
PyKey 87 TKL
PyboardV1_1
RF.Guru RP2040
RGBTouch Mini
RP2.65-F
RP2040 Stamp
RP2350 Stamp
RP2350 Stamp XL
Raspberry Breadstick
Raspberry Pi 4B
Raspberry Pi Compute Module 4
Raspberry Pi Compute Module 4 IO Board
Raspberry Pi Pico
Raspberry Pi Pico 2
Raspberry Pi Pico W
Raspberry Pi Zero
Raspberry Pi Zero 2W
Raspberry Pi Zero W
Robo HAT MM1 M4
S2Mini
S2Pico
SAM E54 Xplained Pro
SAM32v26
SPRESENSE
SQFMI Watchy
SSCI ISP1807 Dev Board
SSCI ISP1807 Micro Board
ST STM32F746G Discovery
STM32F411E_DISCO
STM32F412G_DISCO
STM32F4_DISCO
Saola 1 w/Wroom
Saola 1 w/Wrover
Seeed Studio XIAO ESP32C3
Seeed XIAO nRF52840 Sense
Seeed Xiao ESP32-C6 4MB Flash 512KB SRAM
Seeed Xiao ESP32-S3 Sense
Seeeduino Wio Terminal
Seeeduino XIAO RP2040
Seeeduino XIAO RP2350
Silicognition LLC M4-Shim
Silicognition LLC RP2040-Shim
SparkFun MicroMod RP2040 Processor
SparkFun MicroMod SAMD51 Processor
SparkFun MicroMod nRF52840 Processor
SparkFun Pro Micro RP2040
SparkFun Pro Micro RP2350
SparkFun Pro nRF52840 Mini
SparkFun STM32 MicroMod Processor
SparkFun Teensy MicroMod Processor
SparkFun Thing Plus - RP2040
SparkFun Thing Plus - SAMD51
SparkFun Thing Plus - STM32
Spotpear ESP32C3 LCD 1.44
Sprite_v2b
Sunton ESP32-2424S012
Sunton-ESP32-8048S050
Sunton-ESP32-8048S070
SuperMini NRF52840
Swan R5
TG-Boards' Datalore IP M4
TG-Watch
THUNDERPACK_v11
THUNDERPACK_v12
TTGO T8 ESP32-S2-WROOM
Targett Module Clip w/Wroom
Targett Module Clip w/Wrover
Teensy 4.0
Teensy 4.1
Teknikio Bluebird
The Open Book Feather
ThingPulse Pendrive S3
TinkeringTech ScoutMakes Azul
TinyC6
TinyPICO
TinyPICO Nano
TinyS2
TinyS3
TinyWATCH S3
UARTLogger II
VCC-GND Studio YD RP2040
VCC-GND YD-ESP32-S3 (N16R8)
VCC-GND YD-ESP32-S3 (N8R8)
VIDI X V1.1
W5100S-EVB-Pico
W5500-EVB-Pico
WK-50 Trackball Keyboard
WSC-1450
WarmBit BluePixel nRF52840
Waveshare ESP32-S2-Pico
Waveshare ESP32-S2-Pico-LCD
Waveshare ESP32-S3-GEEK
Waveshare ESP32-S3-Pico
Waveshare ESP32-S3-Tiny
Waveshare ESP32-S3-Zero
Waveshare ESP32S3 LCD 1.28
Waveshare RP2040-GEEK
Waveshare RP2040-LCD-0.96
Waveshare RP2040-LCD-1.28
Waveshare RP2040-One
Waveshare RP2040-PiZero
Waveshare RP2040-Plus (16MB)
Waveshare RP2040-Plus (4MB)
Waveshare RP2040-TOUCH-LCD-1.28
Waveshare RP2040-Tiny
Waveshare RP2040-Zero
WeAct ESP32-C6 (4MB)
WeAct ESP32-C6 (8MB)
WeAct Studio Pico
WeAct Studio Pico 16MB
WeMos LOLIN32 Lite
Wemos Lolin C3 Mini
Wemos Lolin C3 Pico
Winterbloom Sol
WisdPi Ardu2040M
WisdPi Tiny RP2040
iLabs Challenger 840
iMX RT 1020 EVK
iMX RT 1040 EVK
iMX RT 1050 EVKB
iMX RT 1060 EVK
iMX RT 1060 EVKB
iMX RT1011 Nano Kit
nanoESP32-S2 w/Wrover
nanoESP32-S2 w/Wroom
nice!nano
nullbits Bit-C PRO
senseBox MCU-S2 ESP32S2
splitkb.com Liatris
stm32f411ce-blackpill
stm32f411ce-blackpill-with-flash
sunton_esp32_2432S028
sunton_esp32_2432S032C
takayoshiotake Octave RP2040
uGame22

class bitbangio.I2C(scl: microcontroller.Pin, sda: microcontroller.Pin, *, frequency: int = 400000, timeout: int = 255)

Two wire serial protocol

I2C is a two-wire protocol for communicating between devices. At the physical level it consists of 2 wires: SCL and SDA, the clock and data lines respectively.

See also

Using this class directly requires careful lock management. Instead, use I2CDevice to manage locks.

See also

Using this class to directly read registers requires manual bit unpacking. Instead, use an existing driver or make one with Register data descriptors.

Parameters:

scl (Pin) – The clock pin
sda (Pin) – The data pin
frequency (int) – The clock frequency of the bus
timeout (int) – The maximum clock stretching timeout in microseconds

deinit() → None: Releases control of the underlying hardware so other classes can use it.

__enter__() → I2C: No-op used in Context Managers.

__exit__() → None: Automatically deinitializes the hardware on context exit. See Lifetime and ContextManagers for more info.

probe(address: int) → List[int]

Check if a device at the specified address responds.

Parameters:: address (int) – 7-bit device address
Returns:: True if a device at address responds; False otherwise
Return type:: bool

scan() → List[int]: Scan all I2C addresses between 0x08 and 0x77 inclusive and return a list of those that respond. A device responds if it pulls the SDA line low after its address (including a read bit) is sent on the bus.

try_lock() → bool: Attempts to grab the I2C lock. Returns True on success.

unlock() → None: Releases the I2C lock.

readfrom_into(address: int, buffer: circuitpython_typing.WriteableBuffer, *, start: int = 0, end: int = sys.maxsize) → None

Read into buffer from the device selected by address. The number of bytes read will be the length of buffer. At least one byte must be read.

If start or end is provided, then the buffer will be sliced as if buffer[start:end]. This will not cause an allocation like buf[start:end] will so it saves memory.

Parameters:

address (int) – 7-bit device address
buffer (WriteableBuffer) – buffer to write into
start (int) – Index to start writing at
end (int) – Index to write up to but not include

writeto(address: int, buffer: circuitpython_typing.ReadableBuffer, *, start: int = 0, end: int = sys.maxsize) → None

Write the bytes from buffer to the device selected by address and then transmits a stop bit. Use writeto_then_readfrom when needing a write, no stop and repeated start before a read.

If start or end is provided, then the buffer will be sliced as if buffer[start:end] were passed, but without copying the data. The number of bytes written will be the length of buffer[start:end].

Writing a buffer or slice of length zero is permitted, as it can be used to poll for the existence of a device.

Parameters:

address (int) – 7-bit device address
buffer (ReadableBuffer) – buffer containing the bytes to write
start (int) – beginning of buffer slice
end (int) – end of buffer slice; if not specified, use len(buffer)

writeto_then_readfrom(address: int, out_buffer: circuitpython_typing.ReadableBuffer, in_buffer: circuitpython_typing.ReadableBuffer, *, out_start: int = 0, out_end: int = sys.maxsize, in_start: int = 0, in_end: int = sys.maxsize) → None

Write the bytes from out_buffer to the device selected by address, generate no stop bit, generate a repeated start and read into in_buffer. out_buffer and in_buffer can be the same buffer because they are used sequentially.

If out_start or out_end is provided, then the buffer will be sliced as if out_buffer[out_start:out_end] were passed, but without copying the data. The number of bytes written will be the length of out_buffer[start:end].

If in_start or in_end is provided, then the input buffer will be sliced as if in_buffer[in_start:in_end] were passed, The number of bytes read will be the length of out_buffer[in_start:in_end].

Parameters:

address (int) – 7-bit device address
out_buffer (ReadableBuffer) – buffer containing the bytes to write
in_buffer (WriteableBuffer) – buffer to write into
out_start (int) – beginning of out_buffer slice
out_end (int) – end of out_buffer slice; if not specified, use len(out_buffer)
in_start (int) – beginning of in_buffer slice
in_end (int) – end of in_buffer slice; if not specified, use len(in_buffer)

class bitbangio.SPI(clock: microcontroller.Pin, MOSI: microcontroller.Pin | None = None, MISO: microcontroller.Pin | None = None)

A 3-4 wire serial protocol

SPI is a serial protocol that has exclusive pins for data in and out of the main device. It is typically faster than I2C because a separate pin is used to select a device rather than a transmitted address. This class only manages three of the four SPI lines: clock, MOSI, MISO. Its up to the client to manage the appropriate select line, often abbreviated CS or SS. (This is common because multiple secondaries can share the clock, MOSI and MISO lines and therefore the hardware.)

Construct an SPI object on the given pins.

See also

Using this class directly requires careful lock management. Instead, use SPIDevice to manage locks.

See also

Using this class to directly read registers requires manual bit unpacking. Instead, use an existing driver or make one with Register data descriptors.

Parameters:

clock (Pin) – the pin to use for the clock.
MOSI (Pin) – the Main Out Selected In pin.
MISO (Pin) – the Main In Selected Out pin.

deinit() → None: Turn off the SPI bus.

__enter__() → SPI: No-op used by Context Managers.

__exit__() → None: Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.

configure(*, baudrate: int = 100000, polarity: int = 0, phase: int = 0, bits: int = 8) → None

Configures the SPI bus. Only valid when locked.

Parameters:

baudrate (int) – the clock rate in Hertz
polarity (int) – the base state of the clock line (0 or 1)
phase (int) – the edge of the clock that data is captured. First (0) or second (1). Rising or falling depends on clock polarity.
bits (int) – the number of bits per word

try_lock() → bool

Attempts to grab the SPI lock. Returns True on success.

Returns:: True when lock has been grabbed
Return type:: bool

unlock() → None: Releases the SPI lock.

write(buf: circuitpython_typing.ReadableBuffer, *, start: int = 0, end: int = sys.maxsize) → None

Write the data contained in buf. Requires the SPI being locked. If the buffer is empty, nothing happens.

If start or end is provided, then the buffer will be sliced as if buffer[start:end] were passed, but without copying the data. The number of bytes written will be the length of buffer[start:end].

Parameters:

buffer (ReadableBuffer) – buffer containing the bytes to write
start (int) – beginning of buffer slice
end (int) – end of buffer slice; if not specified, use len(buffer)

readinto(buffer: circuitpython_typing.WriteableBuffer, *, start: int = 0, end: int = sys.maxsize, write_value: int = 0) → None

Read into buffer while writing write_value for each byte read. The SPI object must be locked. If the number of bytes to read is 0, nothing happens.

If start or end is provided, then the buffer will be sliced as if buffer[start:end] were passed. The number of bytes read will be the length of buffer[start:end].

Parameters:

buffer (WriteableBuffer) – read bytes into this buffer
start (int) – beginning of buffer slice
end (int) – end of buffer slice; if not specified, use len(buffer)
write_value (int) – value to write while reading

write_readinto(out_buffer: circuitpython_typing.ReadableBuffer, in_buffer: circuitpython_typing.WriteableBuffer, *, out_start: int = 0, out_end: int = sys.maxsize, in_start: int = 0, in_end: int = sys.maxsize) → None

Write out the data in out_buffer while simultaneously reading data into in_buffer. The SPI object must be locked.

If out_start or out_end is provided, then the buffer will be sliced as if out_buffer[out_start:out_end] were passed, but without copying the data. The number of bytes written will be the length of out_buffer[out_start:out_end].

If in_start or in_end is provided, then the input buffer will be sliced as if in_buffer[in_start:in_end] were passed, The number of bytes read will be the length of out_buffer[in_start:in_end].

The lengths of the slices defined by out_buffer[out_start:out_end] and in_buffer[in_start:in_end] must be equal. If buffer slice lengths are both 0, nothing happens.

Parameters:

out_buffer (ReadableBuffer) – write out bytes from this buffer
in_buffer (WriteableBuffer) – read bytes into this buffer
out_start (int) – beginning of out_buffer slice
out_end (int) – end of out_buffer slice; if not specified, use len(out_buffer)
in_start (int) – beginning of in_buffer slice
in_end (int) – end of in_buffer slice; if not specified, use len(in_buffer)

bitbangio – Digital protocols implemented by the CPU

`bitbangio` – Digital protocols implemented by the CPU