UMCPMIO(4)

NAME
umcpmio - Microchip Technologies MCP2210, MCP2221/MCP2221A multi-io bridge

SYNOPSIS
umcpmio* at uhidev? reportid ?
gpio* at gpiobus?
spi* at umcpmio?
iic* at umcpmio? # or
iic* at i2cbus?

DESCRIPTION
The umcpmio driver provides support for the MCP2210 and MCP2221/MCP2221A multi-io bridge chips. The MCP2210 provides 9 simple gpio pins with multiple functions that attach as a gpio(4) device and the ability to do SPI via the spi(4) framework. The pins function as gpio(4) pins or as chip select for the spi(4) function. The MCP2221 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 on the MCP2210
There are 9 basic gpio pins available with the following functions:

Pin | GPIO | ALT0 | ALT3 | ALT4 | ALT5 | ALT6
GP0 | I/O | CS | - | - | - | -
GP1 | I/O | CS | - | - | - | -
GP2 | I/O | CS | SSPND | - | - | -
GP3 | I/O | CS | SPI activity | - | - | -
GP4 | I/O | CS | LOWPWR | - | - | -
GP5 | I/O | CS | USBCFG | - | - | -
GP6 | I/O | CS | Falling edge | Rising edge | Low pulse | High pulse
GP7 | I/O | CS | Release ACK | - | - | -
GP8 | I | - | Release REQ | - | - | -

The IRQ counter on GP6 can be read with a sysctl(8). The manor in which the GP6 IRQ counter detects the event is configured by setting it to ALT3 to ALT6. GP8 is only an input pin when configured for gpio purposes. The chip select, CS, function will be enabled automatically if a request to use the spi(4) framework is performed that requests the use of the associated chip select pin.

  SPI
The MCP2210 supports a basic SPI engine via the spi(4) framework. Various SPI delays are configured with umcpmioctl(8).

The SPI engine on the MCP2210 only functions in full duplex mode. That is, it is not possible to just send bytes without also receiving them. The driver will queue up any received bytes that might have come though on a transaction and present them to the upstream layer from the queue when asked. This queue will be cleared out for a particular slave address when a configuration call is made against a particular slave device.

Upon making a configuration call to the umcpmio driver, the driver will set the pin associated with the requested slave address to ALT0. Since the spi(4) framework does not support the notion of a session, this pin will never be reset by the umcpmio driver. Further, it is entirely possible to use gpioctl(8) to change the pin assignment in such a way that SPI no longer works as it is also not possible to know if a pin is in use at any moment in time.

  EEPROM
The MCP2210 has 256 bytes of EEPROM available via the /dev/umcpmio0EEP device. Random reads and writes may be performed against this device, but there can only one one opener at a time.

  GPIO on the MCP2221
There are 4 basic gpio pins available with the following functions:

Pin | GPIO | ALT0 | ALT1 | ALT2 | ALT3
GP0 | I/O | UART RX | - | - | SSPND
GP1 | I/O | ADC1 | UART TX | IRQ | Clock output
GP2 | I/O | ADC2 | DAC1 | - | USBCFG
GP3 | I/O | ADC3 | DAC2 | - | 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 MCP2221/MCP2221A 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 on the MCP2221/MCP2221A 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.

  MCP2210
hw.umcpmio0.spi.verbose
    Enable or disable verbose connection reset messages when there are errors.

hw.umcpmio0.spi.busy_delay
    When the MCP2210 is busy, use busy_delay number of ms to wait before trying the operation again. The default is 0 as there usually will not be any reason is wait.

hw.umcpmio0.spi.retry_busy_chipdrain
hw.umcpmio0.spi.retry_busy_transfer
    The number of times to retry either a chipdrain or transfer operation. A chipdrain is used when the chip has sent back data, but the upstream is not ready for it yet. A transfer is a normal SPI transfer.

hw.umcpmio0.gpio.counter
hw.umcpmio0.gpio.reset_counter
    When the GP6 pin is set to ALT3 to ALT6, this sysctl reads back the counter. To reset the counter write 1 to the reset_counter sysctl. The counter will also be reset if any pin changes from a input or output pin to one of the ALT functions or vise versa. The trigger for this could be the use of gpioctl(8) or if the pin is changed to become a CS from a general I/O pin for the spi(4) infrastructure.

  MCP2221/MCP2221A
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 on the MCP2221/MCP2221A.

/dev/umcpmio0EEP
    Device file that interacts with the EEPROM on the MCP2210.

SEE ALSO
gpio(4), iic(4), spi(4), sysctl(8), umcpmioctl(8)

HISTORY
The umcpmio driver first appeared in NetBSD 11.0. Support for the MCP2210 was added in NetBSD 12.0.

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

BUGS
The gpio pins on the these two chips 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 of the MCP2221/MCP2221A 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, 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.

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 umcpmio.

Please note that the umcpmio 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.

On the MCP2210, changing any pin from INPUT or OUTPUT to ALTx or vise versa has to rewrite some of the setting for all pins. A consequence of doing this is that for a very brief time, the default direction and values will be set on all pins. This has the biggest impact on OUTPUT pins which might generate a small pulse. This behavior really can't be avoided as there is no way with the MCP2210 to write the configuration of just one pin at a time. For this same reason, the IRQ event counter will be reset if any pin switches from INPUT or OUTPUT to ALTx or vise versa.

The MCP2210 supports active high or active low CS signals per CS. However, the spi(4) framework does not have any way to specify the direction of the CS signal, so the only SPI CS signal supported is the usual active low signal.