[lm-sensors] i2c device w/o registers

[lm-sensors] i2c device w/o registers

[Randy]

I have an ADC (MCP3424) that doesn't use registers/commands. 

To configure the device, you simply write the configuration to the appropriate 
I2C device address.

To read the sensor data, you simply issue a read to the device, which will 
return the ADC sample and the current control register (3 or 4 bytes total, 
depending on mode).

All the commands in i2c-tools and the i2c drivers, except for the read/write 
byte commands, want to take an additional register parameter.  This extra param 
going over the wire messes up the chip.

Is there any simple way to support devices that don't support registers?  I 
searched the archive, and found some requests for a i2c_smbus_read_word() 
command, but that's about it.

thanks,

Randy


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Re: [lm-sensors] i2c device w/o registers

[Jean Delvare]

Hi Randy,

On Mon, 6 Jun 2011 17:25:10 -0700 (PDT), Randy wrote:
> I have an ADC (MCP3424) that doesn't use registers/commands. 
> 
> To configure the device, you simply write the configuration to the appropriate 
> I2C device address.
> 
> To read the sensor data, you simply issue a read to the device, which will 
> return the ADC sample and the current control register (3 or 4 bytes total, 
> depending on mode).
> 
> All the commands in i2c-tools and the i2c drivers, except for the read/write 
> byte commands, want to take an additional register parameter.  This extra param 
> going over the wire messes up the chip.
> 
> Is there any simple way to support devices that don't support registers?  I 
> searched the archive, and found some requests for a i2c_smbus_read_word() 
> command, but that's about it.

This question would have better been asked on the linux-i2c list,
methinks.

Anyway, the I2C commands you need aren't part of the SMBus command
subset, so you have to use raw I2C messaging. The functions you need
are i2c_master_send() and i2c_master_recv() in kernel space. In
user space, you'd simply call read() and write() on the device node. I
don't think there's any example of this in i2c-tools, but the i2c-dev
driver supports it.

-- 
Jean Delvare

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Re: [lm-sensors] i2c device w/o registers

[Ben Dooks]

On Mon, Jun 06, 2011 at 05:25:10PM -0700, Randy wrote:
> I have an ADC (MCP3424) that doesn't use registers/commands. 
> 
> To configure the device, you simply write the configuration to the appropriate 
> I2C device address.
> 
> To read the sensor data, you simply issue a read to the device, which will 
> return the ADC sample and the current control register (3 or 4 bytes total, 
> depending on mode).
> 
> All the commands in i2c-tools and the i2c drivers, except for the read/write 
> byte commands, want to take an additional register parameter.  This extra param 
> going over the wire messes up the chip.
> 
> Is there any simple way to support devices that don't support registers?  I 
> searched the archive, and found some requests for a i2c_smbus_read_word() 
> command, but that's about it.

you can send direct i2c commands to the device without any register
access by using i2c_transfer with an "struct i2c_msg" to do anything
you like.

-- 
Ben Dooks, ben@fluff.org, http://www.fluff.org/ben/

Large Hadron Colada: A large Pina Colada that makes the universe disappear.


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Re: [lm-sensors] i2c device w/o registers

[Randy]

Thanks.  I did the equivalent of this by modifying i2c_smbus_xfer_emulated() and 
making my own read message, and it works.

Maybe I'll try to call i2c_transfer directly as your recommended, since that 
sounds cleaner.

thanks,

Randy



----- Original Message ----
From: Ben Dooks <ben@trinity.fluff.org>
To: Randy <singularity_2@yahoo.com>
Cc: lm-sensors@lm-sensors.org
Sent: Tue, June 7, 2011 1:18:39 AM
Subject: Re: [lm-sensors] i2c device w/o registers


On Mon, Jun 06, 2011 at 05:25:10PM -0700, Randy wrote:
> I have an ADC (MCP3424) that doesn't use registers/commands. 
> 
> To configure the device, you simply write the configuration to the appropriate 

> I2C device address.
> 
> To read the sensor data, you simply issue a read to the device, which will 
> return the ADC sample and the current control register (3 or 4 bytes total, 
> depending on mode).
> 
> All the commands in i2c-tools and the i2c drivers, except for the read/write 
> byte commands, want to take an additional register parameter.  This extra param 
>
> going over the wire messes up the chip.
> 
> Is there any simple way to support devices that don't support registers?  I 
> searched the archive, and found some requests for a i2c_smbus_read_word() 
> command, but that's about it.

you can send direct i2c commands to the device without any register
access by using i2c_transfer with an "struct i2c_msg" to do anything
you like.

-- 
Ben Dooks, ben@fluff.org, http://www.fluff.org/ben/

Large Hadron Colada: A large Pina Colada that makes the universe disappear.

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Re: [lm-sensors] i2c device w/o registers

[Guenter Roeck]

On Tue, Jun 07, 2011 at 02:57:59PM -0400, Randy wrote:
> Thanks.  I did the equivalent of this by modifying i2c_smbus_xfer_emulated() and 
> making my own read message, and it works.
> 
> Maybe I'll try to call i2c_transfer directly as your recommended, since that 
> sounds cleaner.
> 
Might be a good idea, at least if you plan to submit your driver ;).

Guenter

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Re: [lm-sensors] i2c device w/o registers

[Randy]

read() and write() worked well.  I just had to set the slave address w/ ioctl()

thanks,

Randy



----- Original Message ----
From: Jean Delvare <khali@linux-fr.org>
To: Randy <singularity_2@yahoo.com>
Cc: lm-sensors@lm-sensors.org
Sent: Mon, June 6, 2011 11:48:12 PM
Subject: Re: [lm-sensors] i2c device w/o registers

Hi Randy,

On Mon, 6 Jun 2011 17:25:10 -0700 (PDT), Randy wrote:
> I have an ADC (MCP3424) that doesn't use registers/commands. 
> 
> To configure the device, you simply write the configuration to the appropriate 

> I2C device address.
> 
> To read the sensor data, you simply issue a read to the device, which will 
> return the ADC sample and the current control register (3 or 4 bytes total, 
> depending on mode).
> 
> All the commands in i2c-tools and the i2c drivers, except for the read/write 
> byte commands, want to take an additional register parameter.  This extra param 
>
> going over the wire messes up the chip.
> 
> Is there any simple way to support devices that don't support registers?  I 
> searched the archive, and found some requests for a i2c_smbus_read_word() 
> command, but that's about it.

This question would have better been asked on the linux-i2c list,
methinks.

Anyway, the I2C commands you need aren't part of the SMBus command
subset, so you have to use raw I2C messaging. The functions you need
are i2c_master_send() and i2c_master_recv() in kernel space. In
user space, you'd simply call read() and write() on the device node. I
don't think there's any example of this in i2c-tools, but the i2c-dev
driver supports it.

-- 
Jean Delvare


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Re: [lm-sensors] i2c device w/o registers

[Randy]

Thanks Jean.  The user-space method worked great.

For kernel space access, is there an easy way to get a reference to the i2c 
client (struct i2c_client *client) to pass to i2c_master_recv(), since I can't 
do open() via a kernel module?  I've searched all around, but can't find such an 
example.  I think my system would be cleaner as a kernel module (my I2C devices 
are ADCs, so I'd use a different analog driver over i2c for different chips in 
my system, and they'd all publish common analog read commands...).

Thanks,

Randy



----- Original Message ----
From: Jean Delvare <khali@linux-fr.org>
To: Randy <singularity_2@yahoo.com>
Cc: lm-sensors@lm-sensors.org
Sent: Mon, June 6, 2011 11:48:12 PM
Subject: Re: [lm-sensors] i2c device w/o registers

Hi Randy,

On Mon, 6 Jun 2011 17:25:10 -0700 (PDT), Randy wrote:
> I have an ADC (MCP3424) that doesn't use registers/commands. 
> 
> To configure the device, you simply write the configuration to the appropriate 

> I2C device address.
> 
> To read the sensor data, you simply issue a read to the device, which will 
> return the ADC sample and the current control register (3 or 4 bytes total, 
> depending on mode).
> 
> All the commands in i2c-tools and the i2c drivers, except for the read/write 
> byte commands, want to take an additional register parameter.  This extra param 
>
> going over the wire messes up the chip.
> 
> Is there any simple way to support devices that don't support registers?  I 
> searched the archive, and found some requests for a i2c_smbus_read_word() 
> command, but that's about it.

This question would have better been asked on the linux-i2c list,
methinks.

Anyway, the I2C commands you need aren't part of the SMBus command
subset, so you have to use raw I2C messaging. The functions you need
are i2c_master_send() and i2c_master_recv() in kernel space. In
user space, you'd simply call read() and write() on the device node. I
don't think there's any example of this in i2c-tools, but the i2c-dev
driver supports it.

-- 
Jean Delvare


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Re: [lm-sensors] i2c device w/o registers

[Randy]

I got it working by creating a very basic slave device driver for my ADC 
converter.

For anyone in the same situation, there is a good link here: 
http://www.embedded-bits.co.uk/?s=i2c

But you're right, this was probably more appropriate for the linux i2c list.

Thanks.



----- Original Message ----
From: Jean Delvare <khali@linux-fr.org>
To: Randy <singularity_2@yahoo.com>
Cc: lm-sensors@lm-sensors.org
Sent: Mon, June 6, 2011 11:48:12 PM
Subject: Re: [lm-sensors] i2c device w/o registers

Hi Randy,

On Mon, 6 Jun 2011 17:25:10 -0700 (PDT), Randy wrote:
> I have an ADC (MCP3424) that doesn't use registers/commands. 
> 
> To configure the device, you simply write the configuration to the appropriate 

> I2C device address.
> 
> To read the sensor data, you simply issue a read to the device, which will 
> return the ADC sample and the current control register (3 or 4 bytes total, 
> depending on mode).
> 
> All the commands in i2c-tools and the i2c drivers, except for the read/write 
> byte commands, want to take an additional register parameter.  This extra param 
>
> going over the wire messes up the chip.
> 
> Is there any simple way to support devices that don't support registers?  I 
> searched the archive, and found some requests for a i2c_smbus_read_word() 
> command, but that's about it.

This question would have better been asked on the linux-i2c list,
methinks.

Anyway, the I2C commands you need aren't part of the SMBus command
subset, so you have to use raw I2C messaging. The functions you need
are i2c_master_send() and i2c_master_recv() in kernel space. In
user space, you'd simply call read() and write() on the device node. I
don't think there's any example of this in i2c-tools, but the i2c-dev
driver supports it.

-- 
Jean Delvare


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