Revision as of 12:18, 3 February 2009

Introduction

The MAX1027 is an 8 channels 10 bits analog-to-digital converter (ADC) with an internal reference and an internal temperature sensor. It is mounted (in option) on the APF9328 boards. To know if you have one on your board, take a look at the connectors side:

figure 1 - MAX1027 localisation

If you don't have one and are a good electrician, you can order a sample at Maxim's website and solder it directly on your board (footprint is available).

Hardware interface

Warning: The 8 inputs voltage range is [0 - 3,3V]. Don't try to put higher voltage on ADC inputs.

By default internal reference voltage is used (2,5V), so if you apply analog values > 2,5V, they will be truncated. The i.MXL SPI_1 interface is used to communicate with the device.

figure 2 - MAX1027 connections

If you want to use the MAX1027 then you will have to connect #EOC pin (End Of Conversion) and #CNVST pin (conversion start) to two i.MXL GPIOs. By default the driver is using:

• PA13 (CSI_HSYNC) for #EOC
• and PA14 (CSI_PIXCLK) for #CNVST

So for example on the APF9328DevFull board you will have to connect:

• pin 11 of ADC connector (right of the Ethernet one) to pin 12 of CSI connector (below RS232 one)
• and pin 10 of the ADC connector to pin 14 of the CSI connector

Driver

Depending on your needs (ie sampling slow or fast signals) there are 2 ways to use the max1027 Linux driver:

• for slow signals (temperature or battery level monitoring), the driver can be strictly controlled from its /sys interface: /sys/bus/spi/devices/spiN.0/ (N depending on the number of SPI devices declared for your target). Moreover, if needed (lm-sensors & Co), you can add it a Linux Hardware Monitoring API (hwmon) compatible/standardized interface: /sys/class/hwmon/hwmonN/device/ (N depending on the ID given by hwmon). This interface mimics the /sys/bus/spi/devices/ one.
• for "fast" signals, the driver has a /dev interface which can be configured through /sys/bus/spi/devices/spiX.0/.

Installation

Note: Max1027 driver is now by default installed on standard rootfs so following instructions are only given as reference.

• From the armadeus/ top directory:

 $ make linux26-menuconfig

• Then select in

 Device Drivers  ---> 
    [*] SPI support  ---> 
        <M>   Freescale iMX SPI controller

• If you want to have the hwmon compatible interface, select in

 Device Drivers  ---> 
    <M> Hardware Monitoring support (Module)

• and then choose MAX1027 driver in

 Device Drivers  
    ---> Armadeus specific drivers  
        <M>   Armadeus Max1027 ADC driver (fast version)

• Once the new configuration saved, rebuild your system:

 $ make

and copy hwmon.ko and max1027.ko driver to your target or reflash your rootfs.

Usage

On the target, the driver can be started like this:

 # modprobe spi_imx
 # modprobe max1027
 max1027 v0.3 successfully probed !

"Slow" & configuration interface

Several interfaces in /sys/bus/spi/devices/spi... are created in order to:

• read the 8 analog inputs values: inx_input (in mV)
• read the temperature: temp1_input (in m°C)
• modify the max1027 registers: conversion, setup & averaging

 # ls /sys/bus/spi/devices/spi1.0/
 averaging    driver       in2_input    in5_input    modalias     temp1_input
 bus          in0_input    in3_input    in6_input    setup        uevent
 conversion   in1_input    in4_input    in7_input    subsystem

An input can be read like that:

 # cat /sys/bus/spi/devices/spi1.0/in0_input

The temperature can be read like that:

 # cat /sys/bus/spi/devices/spi1.0/temp1_input

Warning: These values are only updated each time you launch a conversion, ie accessing the Max1027 conversion register, after having configured setup register accordingly. So this interface is only suitable to measure slow evolving greats. Example: # let set=0x62; echo $set > /sys/bus/spi/devices/spi1.0/setup # let conv=0x87; echo $conv > /sys/bus/spi/devices/spi1.0/conversion (launch 1 conversion of temp & AN0) # cat /sys/bus/spi/devices/spi1.0/temp1_input 32750 (m°C) # cat /sys/bus/spi/devices/spi1.0/in0_input 1135 (mV)

"Fast" interface (frequencies > 10Hz)

CNVST pin is used to start the conversion, so you "only" have 7 analog inputs. In that case you can use /dev interface (using blocking read to wait end of conversion). To create /dev nodes you can use the loadmax.sh script located in armadeus/target/linux/modules/max1027. As driver MAJOR number is dynamically allocated, you may need to update /dev depending on the drivers loaded on you system.

• first, the conversion mode has to be chosen (channel 0->6 and temp):

 # let set=0xb1; echo $set > /sys/bus/spi/devices/spi1.0/conversion

• and eventually the averaging and setup registers as well (refer to the max1027 documentation for more details):

 # let set=0x48; echo $set > /sys/bus/spi/devices/spi1.0/setup
 # let set=0x20; echo $set > /sys/bus/spi/devices/spi1.0/averaging

• repeatedly read value of analog input 0 (variable sampling rate = depends on system load):

 # cat /dev/max1027/AIN0

• read analog input 0 once:

 # time dd if=/dev/max1027/AIN0 bs=2 count=1 > tmp.bin
 # hexdump tmp.bin

This mode is activated by default in the Max1027 driver. If you switched to "slow" mode you can activate "fast" mode again with:

 # let set=0x48; echo $set > /sys/bus/spi/devices/spi1.0/setup

Chip registers configuration

Independent of the mode, /sys interfaces allow direct access to the corresponding register in the MAX1027:

 # let conv=0xb1; echo $conv > /sys/bus/spi/devices/spi1.0/conversion

You can also get current (hexadecimal) values of conversion, averaging and setup registers with (for example):

 # cat /sys/bus/spi/devices/spi1.0/setup
 0x62

For more details on how to use these registers, take a look at the datasheet.

Shell examples

• Get channel 0 and temperature values:

 # let conv=0x87; echo $conv > /sys/bus/spi/devices/spi1.0/conversion
 # cat /sys/class/hwmon/hwmon0/device/temp1_input
 # cat /sys/class/hwmon/hwmon0/device/in0_input

• Get channels [0-6] and temperature values:

 # let conv=0xb1; echo $conv > /sys/bus/spi/devices/spi1.0/conversion

• Get 4 average values (of 32 conversions) for channel 0:

 # let avg=0x3c; echo $avg > /sys/bus/spi/devices/spi1.0/averaging
 # let conv=0x84; echo $conv > /sys/bus/spi/devices/spi1.0/conversion

Links

• MAX1027 datasheet on Maxim website
• hwmon documentation