UMCPMIO(4)

UMCPMIO(4) | Device Drivers Manual | UMCPMIO(4)

# NAME

`umcpmio` — Driver for Microchip Technologies MCP2221 / MCP2221A multi-io bridge.

# SYNOPSIS

`umcpmio* at uhidev? reportid ?`
`gpio* at gpiobus?`
`iic* at umcpmio? or`
`iic* at i2cbus?`

# DESCRIPTION

The `umcpmio` driver provides support for the MCP2221 / MCP2221A multi-io bridge chip. The chip provides 4 simple gpio pins with multiple functions that attach as a gpio(4) device, an I2C port that attaches as an iic(4) device and a UART serial port that attaches using umodem(4) as a normal ucom(4) ttyU* device. The UART is presented as one USB function, while the GPIO and I2C pins are presented as a second HID USB function.

## GPIO

There are 4 basic gpio pins available with the following functions:

Assignment | GP0 | GP1 | GP2 | GP3
GPIO | GPIO | GPIO | GPIO | GPIO
ALT0 | UART RX | ADC1 | ADC2 | ADC3
ALT1 | - | UART TX | DAC1 | DAC2
ALT2 | - | IRQ | - | -
ALT3 | SSPND | Clock output | USBCFG | I2C activity

ADC1, ADC2 and ADC3 are independent of each other and each 10 bits in length. To utilize one of the ADC pins, an open(2) is performed against /dev/umcpmio0GP1, /dev/umcpmio0GP2 or /dev/umcpmio0GP3 with only the `O_RDONLY` flag set. Reads against the open file descriptor will produce uint16_t values.

There is actually only one DAC present in the chip, but it is mirrored to GP2 and GP3 if the pin is set to ALT1. The DAC is 5 bits in length, and to use it, an open(2) is performed against /dev/umcpmio0GP2 or /dev/umcpmio0GP3 with only the `O_WRONLY` flag set. Writes of uint8_t bytes to the file descriptor will result in an analog signal being created on the output pin.

The clock output is derived from the USB clock of 48MHz. The duty cycle and clock divider can be adjusted with sysctl(8) variables. To utilize GP1 as the clock output, the ALT3 function can be set with gpioctl(8) command.

## I2C

The chip supports a hardware I2C port with a simple scripting engine. When the driver attaches, the I2C speed is set to 100Kb/s. The ability to perform an I2C READ without a STOP is not supported by the MCP2221 / MCP2221A engine and the driver turns a READ without STOP into a READ with STOP. This behavior is just an attempt to allow a device to function, and it may not work for any particular device. In particular, it is known that the ds2482ow(4) device will not work as expected.

The MCP2221 / MCP2221A chip will automatically detect and deal with a device that uses I2C clock stretching.

## UART

The UART utilizes the umodem(4) driver. The UART function of the chip only supports 8-N-1 communications.

# SYSCTL VARIABLES

The following sysctl(3) variables are provided:

`hw.umcpmio0.debug`
`hw.umcpmio0.dump_buffers`
  If `UMCPMIO_DEBUG` is defined, additional debugging output can be enabled.

`hw.umcpmio0.response_wait`
`hw.umcpmio0.response_errcnt`
  This is how long the driver will wait for a HID response to come back from the chip. This variable is in microseconds and defaults to 2500. The driver will only allow `response_errcnt` number of errors when waiting for a response from a HID report. This includes timeouts due to exceeding `response_wait`.

`hw.umcpmio0.i2c.reportreadnostop`
  Report on the console if a driver attempts to use an I2C READ without STOP. A READ without STOP is not supported by the MCP2221 / MCP2221A I2C engine and will be turned into a READ with STOP by the driver.

`hw.umcpmio0.i2c.busy_delay`
  The driver checks in a number of cases if the I2C engine is busy and will wait for `busy_delay` microseconds before checking again.

`hw.umcpmio0.i2c.retry_busy_read`
  The number of times to try to do an I2C READ when the engine is busy.

`hw.umcpmio0.i2c.retry_busy_write`
  The number of times to try to do an I2C WRITE when the engine is busy.

`hw.umcpmio0.gpio.clock_duty_cycle`
`hw.umcpmio0.gpio.clock_divider`
  When GP1 is configured to use function ALT3, it will output a clock pulse. The valid values for `clock_duty_cycle` are ‘`75%`’, ‘`50%`’, ‘`25%`’, and ‘`0%`’. That is, 75% of the time a high and 25% of the time a low will be present on the GP1 pin. The valid values for `clock_divider` are ‘`375kHz`’, ‘`750kHz`’, ‘`1.5MHz`’, ‘`3MHz`’, ‘`6MHz`’, ‘`12MHz`’, and ‘`24MHz`’.

`hw.umcpmio0.dac.vref`
`hw.umcpmio0.adc.vref`
  Sets the VREF value for the DAC or ADC. The valid values are ‘`4.096V`’, ‘`2.048V`’, ‘`1.024V`’, ‘`OFF`’, and ‘`VDD`’.

# FILES

/dev/umcpmio0ctl
  A control device for the chip instance that allows for a number of IOCTLs.

/dev/umcpmio0GP1
/dev/umcpmio0GP2
/dev/umcpmio0GP3
  Device files that allow access to the ADC or DAC functions of the associated gpio pin.

# SEE ALSO

gpio(4), iic(4), sysctl(8), umcpmioctl(8)

# HISTORY

The `umcpmio` driver first appeared in NetBSD 11.0.

# AUTHORS

The `umcpmio` driver was written by Brad Spencer <brad@anduin.eldar.org>.

# BUGS

The gpio pins on the MCP2221 / MCP2221A are very slow and one should not expect to be able to rapidly change their state. Even if the problem mentioned below did not exist, one should not expect to be able to use any of the gpio bit banger drivers such as gpioiic(4) or gpioow(4).

The interrupt function on GP1 cannot currently be used because it is currently not possible to attach through the driver. There may be two possible problems going on:

- The gpio(4) framework runs at `IPL_VM` with a spin lock and when it attempts to establish an interrupt that uses the gpio from umcpmio(4), calls are made into the USB stack that will want to wait in a way that is not allowed while holding a spin lock.
- autoconf(9) runs with `KERNEL_LOCK` and during the attachment, this lock is held when calls are made into the USB stack that will cause a wait that is not allowed while holding `KERNEL_LOCK`.

Either or both of these may be going on, but the end result is that the kernel will panic while attempting to perform a USB transfer while another driver is attempting to attach through umcpmio(4).

Likewise, a ‘`gpioctl gpio1 attach ...`’ type call will also panic for the same reason.

The end result is that gpioirq(4), gpiopps(4) and gpioow(4) will not work with the gpio from umcpio(4).

Please note that the umcpmio(4) driver itself can use the USB stack during attachment and there does not appear to be any problems using the GPIO pins or setting GPIO pin configurations. It is only when the driver is a target during another driver's attachment that there is a problem.

The ability to set or change values in most of the chip's FLASH memory is not supported. This includes changing the configuration protection password. Likewise, support for entering the configuration protection password does not exist, should a particular chip have password protection enabled.

December 16, 2024 | NetBSD 11.0