---
name: "hm2_spi"
section: "9"
platform: "linux"
package: "linuxcnc-uspace"
version: "1:2.9.4-2+deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/hm2_spi"
---

# hm2\_spi(9)

LinuxCNC HAL driver for the Mesa Electronics SPI Anything IO boards, with HostMot2 firmware.

## NAME

hm2\_spi - LinuxCNC HAL driver for the Mesa Electronics SPI Anything IO boards, with HostMot2 firmware.

## SYNOPSIS

**loadrt hm2\_spi \[config=*"str\[,str...\]"*\] \[spidev\_path=path\[,path...\]\] \[spidev\_rate=*rate\[,rate...\]*\]**

- **config** \[default: ""\]

  HostMot2 config strings, described in the [hostmot2(9)](/hostmot2/9.md) manpage.

- **spidev\_path** \[default: "/dev/spidev1.0"\]

  The path to the spi device node, a character special device in /dev

- **spidev\_rate** \[default: 24000\]

  The desired rate of the SPI clock in kHz.  If the exact specified clock is not available, a lower clock is used.  Due to shortcomings in the spidev API, it is not possible for hal to report the actual clock used.

## DESCRIPTION

hm2\_spi is a device driver that interfaces Mesa's SPI based Anything I/O boards (with the HostMot2 firmware) to the LinuxCNC HAL.

The supported boards are: 7I90HD.

The board must have a compatible firmware loaded on the board by the [mesaflash(1)](/mesaflash/1.md) program.

hm2\_spi is only available when LinuxCNC is configured with "uspace" realtime.

## INTERFACE CONFIGURATION

It is possible for one SPI bus to connect several devices; in this configuration, a master device has several chip select lines.  In order to meet realtime deadlines,  hm2\_spi should be used on a dedicated SPI interface not shared with any other slaves.

## REALTIME PERFORMANCE OF LINUX SPIDEV DRIVERS

As of kernel 3.8, most or all kernel SPI drivers do not achieve the high realtime response rate required for a typical LinuxCNC configuration.  The driver was tested with a modified version of the spi-s3c64xx SPI driver on the Odroid U3 platform.  The patched kernel resides on github ⟨https://github.com/jepler/odroid\\-linux/tree/odroid\\-3.8.13\\-rt⟩.

## SPI CLOCK RATES

The maximum SPI clock of the 7i90 is documented as 50MHz.  Other elements of the data path between HAL and the 7i90 may impose other limitations.

## SEE ALSO

[hostmot2(9)](/hostmot2/9.md)

## LICENSE

GPL