Writing to MCU flash

So we've got this custom product that includes a voltage-controlled 
amplifier.

VCA chips as used in ultrasound and so on have nice low noise at the 
highest gains, but at low gain they stink on ice.  The same is true of 
all transconductance-based VCAs unless you use a zillion stages.

Sooo, we're faking it with a dpot, an op amp with a mux-controlled 
resistor ladder, and an LPC804 Cortex M0+.

The resistor ladder is made out of standard-value Susumu 25-ppm 
resistors, so it's better than the dpot except that the switchable gains 
aren't exactly powers of two.

The simple way of handling this is to have the thing self-calibrate. 
That could be done at power-up and the cal table kept in RAM, or at test 
time with the table in flash.

There's some lore on the net that having the firmware write to the MCU 
flash is a bad idea.

Experiences? Opinions?

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Thu, 24 Jan 2019 10:25:08 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>So we've got this custom product that includes a voltage-controlled 
>amplifier.
>
>VCA chips as used in ultrasound and so on have nice low noise at the 
>highest gains, but at low gain they stink on ice.  The same is true of 
>all transconductance-based VCAs unless you use a zillion stages.
>
>Sooo, we're faking it with a dpot, an op amp with a mux-controlled 
>resistor ladder, and an LPC804 Cortex M0+.
>
>The resistor ladder is made out of standard-value Susumu 25-ppm 
>resistors, so it's better than the dpot except that the switchable gains 
>aren't exactly powers of two.
>
>The simple way of handling this is to have the thing self-calibrate. 
>That could be done at power-up and the cal table kept in RAM, or at test 
>time with the table in flash.
>
>There's some lore on the net that having the firmware write to the MCU 
>flash is a bad idea.
>
>Experiences? Opinions?
>
>Cheers
>
>Phil Hobbs

We have a serial flash cal table on most of our products, written by
the onboard ARM, with a checksum. That works fine.

We have a default cal table in the program, which gets loaded at first
powerup or if the flash table is corrupted. Users are informed of we
are running the default.

The cal table also includes cal table type ID, model number, dash
number, serial number, and cal date.

The cal table resides in a separate soldered-down flash chip from the
program/FPGA code, so we can mail a new plug-in code chip to a
customer without trashing the calibrations. 

We sometimes self-cal some things every powerup, like ADC gains and
offsets, and keep those in ram. But with Susumus, you could cal at
test time. You probably need some nonvolatile cals.





-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

On 1/24/19 10:42 AM, John Larkin wrote:
> On Thu, 24 Jan 2019 10:25:08 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> So we've got this custom product that includes a voltage-controlled
>> amplifier.
>>
>> VCA chips as used in ultrasound and so on have nice low noise at the
>> highest gains, but at low gain they stink on ice.  The same is true of
>> all transconductance-based VCAs unless you use a zillion stages.
>>
>> Sooo, we're faking it with a dpot, an op amp with a mux-controlled
>> resistor ladder, and an LPC804 Cortex M0+.
>>
>> The resistor ladder is made out of standard-value Susumu 25-ppm
>> resistors, so it's better than the dpot except that the switchable gains
>> aren't exactly powers of two.
>>
>> The simple way of handling this is to have the thing self-calibrate.
>> That could be done at power-up and the cal table kept in RAM, or at test
>> time with the table in flash.
>>
>> There's some lore on the net that having the firmware write to the MCU
>> flash is a bad idea.
>>
>> Experiences? Opinions?
>>
>> Cheers
>>
>> Phil Hobbs
> 
> We have a serial flash cal table on most of our products, written by
> the onboard ARM, with a checksum. That works fine.
> 
> We have a default cal table in the program, which gets loaded at first
> powerup or if the flash table is corrupted. Users are informed of we
> are running the default.
> 
> The cal table also includes cal table type ID, model number, dash
> number, serial number, and cal date.
> 
> The cal table resides in a separate soldered-down flash chip from the
> program/FPGA code, so we can mail a new plug-in code chip to a
> customer without trashing the calibrations.
> 
> We sometimes self-cal some things every powerup, like ADC gains and
> offsets, and keep those in ram. But with Susumus, you could cal at
> test time. You probably need some nonvolatile cals.

So you don't ever have firmware write stuff to MCU flash?

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Thursday, January 24, 2019 at 10:25:20 AM UTC-5, Phil Hobbs wrote:
> So we've got this custom product that includes a voltage-controlled 
> amplifier.
> 
> VCA chips as used in ultrasound and so on have nice low noise at the 
> highest gains, but at low gain they stink on ice.  The same is true of 
> all transconductance-based VCAs unless you use a zillion stages.
> 
> Sooo, we're faking it with a dpot, an op amp with a mux-controlled 
> resistor ladder, and an LPC804 Cortex M0+.
> 
> The resistor ladder is made out of standard-value Susumu 25-ppm 
> resistors, so it's better than the dpot except that the switchable gains 
> aren't exactly powers of two.
> 
> The simple way of handling this is to have the thing self-calibrate. 
> That could be done at power-up and the cal table kept in RAM, or at test 
> time with the table in flash.
> 
> There's some lore on the net that having the firmware write to the MCU 
> flash is a bad idea.
> 
> Experiences? Opinions?

Is there anything behind the lore?  Or is it just random mutterings on the idle packets streaming the Internet?  

Many products, many MANY products have the ability to update their firmware.  To do that requires they write to their own flash.  How bad can it be? 

  Rick C.

  - Get 6 months of free supercharging
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On Thu, 24 Jan 2019 11:25:23 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 1/24/19 10:42 AM, John Larkin wrote:
>> On Thu, 24 Jan 2019 10:25:08 -0500, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>> 
>>> So we've got this custom product that includes a voltage-controlled
>>> amplifier.
>>>
>>> VCA chips as used in ultrasound and so on have nice low noise at the
>>> highest gains, but at low gain they stink on ice.  The same is true of
>>> all transconductance-based VCAs unless you use a zillion stages.
>>>
>>> Sooo, we're faking it with a dpot, an op amp with a mux-controlled
>>> resistor ladder, and an LPC804 Cortex M0+.
>>>
>>> The resistor ladder is made out of standard-value Susumu 25-ppm
>>> resistors, so it's better than the dpot except that the switchable gains
>>> aren't exactly powers of two.
>>>
>>> The simple way of handling this is to have the thing self-calibrate.
>>> That could be done at power-up and the cal table kept in RAM, or at test
>>> time with the table in flash.
>>>
>>> There's some lore on the net that having the firmware write to the MCU
>>> flash is a bad idea.
>>>
>>> Experiences? Opinions?
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>> 
>> We have a serial flash cal table on most of our products, written by
>> the onboard ARM, with a checksum. That works fine.
>> 
>> We have a default cal table in the program, which gets loaded at first
>> powerup or if the flash table is corrupted. Users are informed of we
>> are running the default.
>> 
>> The cal table also includes cal table type ID, model number, dash
>> number, serial number, and cal date.
>> 
>> The cal table resides in a separate soldered-down flash chip from the
>> program/FPGA code, so we can mail a new plug-in code chip to a
>> customer without trashing the calibrations.
>> 
>> We sometimes self-cal some things every powerup, like ADC gains and
>> offsets, and keep those in ram. But with Susumus, you could cal at
>> test time. You probably need some nonvolatile cals.
>
>So you don't ever have firmware write stuff to MCU flash?
>
>Cheers
>
>Phil Hobbs

Users can do soft upgrades to the runtime code, but it's often easier
and safer to mail them a chip rather than have them upgrade over
ethernet or USB. There's a lot less to explain.

(Some people just take the box home and plug in the chip there, rather
than dealing with their IT Prevention Department. These people also
take their laptop to Starbucks to get files from us.)

We have two program images in each box, "factory" and "upgrade." A
user can run software (sometimes just a browser) to flash the upgrade
image.

At powerup, a boot loader checks for a valid upgrade image, and runs
it if it looks OK. Otherwise it runs the factory image. If we mail the
user a plugin flash chip, it has only a factory image. RMAs get
reflashed with just the appropriate factory code.

With a hundred or two products having revs and dash numbers and ECOs,
and multiple code revs, and corresponding cal tables, and factory cal
software, we have a nontrivial configuration management problem. It's
important that a user can tell us exactly what is the state of his
box.

We made our own plugin DIP8 adapter for surface-mount serial flash
chips, with room for a label.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

torsdag den 24. januar 2019 kl. 17.30.32 UTC+1 skrev gnuarm.del...@gmail.com:
> On Thursday, January 24, 2019 at 10:25:20 AM UTC-5, Phil Hobbs wrote:
> > So we've got this custom product that includes a voltage-controlled 
> > amplifier.
> > 
> > VCA chips as used in ultrasound and so on have nice low noise at the 
> > highest gains, but at low gain they stink on ice.  The same is true of 
> > all transconductance-based VCAs unless you use a zillion stages.
> > 
> > Sooo, we're faking it with a dpot, an op amp with a mux-controlled 
> > resistor ladder, and an LPC804 Cortex M0+.
> > 
> > The resistor ladder is made out of standard-value Susumu 25-ppm 
> > resistors, so it's better than the dpot except that the switchable gains 
> > aren't exactly powers of two.
> > 
> > The simple way of handling this is to have the thing self-calibrate. 
> > That could be done at power-up and the cal table kept in RAM, or at test 
> > time with the table in flash.
> > 
> > There's some lore on the net that having the firmware write to the MCU 
> > flash is a bad idea.
> > 
> > Experiences? Opinions?
> 
> Is there anything behind the lore?  Or is it just random mutterings on the idle packets streaming the Internet?  
> 
> Many products, many MANY products have the ability to update their firmware.  To do that requires they write to their own flash.  How bad can it be? 
> 

the update procedure does in some cases involve the host 
loading a flash programmer into RAM, so if you are the belt and suspenders 
type you avoid the small risk of having flash programming code in the product 
that could be triggered by accident

torsdag den 24. januar 2019 kl. 16.25.20 UTC+1 skrev Phil Hobbs:
> So we've got this custom product that includes a voltage-controlled 
> amplifier.
> 
> VCA chips as used in ultrasound and so on have nice low noise at the 
> highest gains, but at low gain they stink on ice.  The same is true of 
> all transconductance-based VCAs unless you use a zillion stages.
> 
> Sooo, we're faking it with a dpot, an op amp with a mux-controlled 
> resistor ladder, and an LPC804 Cortex M0+.
> 
> The resistor ladder is made out of standard-value Susumu 25-ppm 
> resistors, so it's better than the dpot except that the switchable gains 
> aren't exactly powers of two.
> 
> The simple way of handling this is to have the thing self-calibrate. 
> That could be done at power-up and the cal table kept in RAM, or at test 
> time with the table in flash.
> 
> There's some lore on the net that having the firmware write to the MCU 
> flash is a bad idea.
> 
> Experiences? Opinions?
> 

I do it on an STM, but there is the small risk of having code in the MCU that 
can program flash possibly being triggered by some cosmic event, 
supply glitch etc.

On Thu, 24 Jan 2019 09:40:56 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>torsdag den 24. januar 2019 kl. 17.30.32 UTC+1 skrev gnuarm.del...@gmail.com:
>> On Thursday, January 24, 2019 at 10:25:20 AM UTC-5, Phil Hobbs wrote:
>> > So we've got this custom product that includes a voltage-controlled 
>> > amplifier.
>> > 
>> > VCA chips as used in ultrasound and so on have nice low noise at the 
>> > highest gains, but at low gain they stink on ice.  The same is true of 
>> > all transconductance-based VCAs unless you use a zillion stages.
>> > 
>> > Sooo, we're faking it with a dpot, an op amp with a mux-controlled 
>> > resistor ladder, and an LPC804 Cortex M0+.
>> > 
>> > The resistor ladder is made out of standard-value Susumu 25-ppm 
>> > resistors, so it's better than the dpot except that the switchable gains 
>> > aren't exactly powers of two.
>> > 
>> > The simple way of handling this is to have the thing self-calibrate. 
>> > That could be done at power-up and the cal table kept in RAM, or at test 
>> > time with the table in flash.
>> > 
>> > There's some lore on the net that having the firmware write to the MCU 
>> > flash is a bad idea.
>> > 
>> > Experiences? Opinions?
>> 
>> Is there anything behind the lore?  Or is it just random mutterings on the idle packets streaming the Internet?  
>> 
>> Many products, many MANY products have the ability to update their firmware.  To do that requires they write to their own flash.  How bad can it be? 
>> 
>
>the update procedure does in some cases involve the host 
>loading a flash programmer into RAM, so if you are the belt and suspenders 
>type you avoid the small risk of having flash programming code in the product 
>that could be triggered by accident
>

Our presumably bug-free boot loader resides in the same flash as the
runtime code images. In the improbable event that the loader gets
trashed, we can send them a new plugin flash or they can send the box
back.

Some simpler products use a single-chip approach, no outboard flash.
They may not be field upgradable.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

On Thu, 24 Jan 2019 10:25:08 -0500, Phil Hobbs wrote:

> So we've got this custom product that includes a voltage-controlled
> amplifier.
> 
> VCA chips as used in ultrasound and so on have nice low noise at the
> highest gains, but at low gain they stink on ice.  The same is true of
> all transconductance-based VCAs unless you use a zillion stages.
> 
> Sooo, we're faking it with a dpot, an op amp with a mux-controlled
> resistor ladder, and an LPC804 Cortex M0+.
> 
> The resistor ladder is made out of standard-value Susumu 25-ppm
> resistors, so it's better than the dpot except that the switchable gains
> aren't exactly powers of two.
> 
> The simple way of handling this is to have the thing self-calibrate.
> That could be done at power-up and the cal table kept in RAM, or at test
> time with the table in flash.
> 
> There's some lore on the net that having the firmware write to the MCU
> flash is a bad idea.
> 
> Experiences? Opinions?
> 
> Cheers
> 
> Phil Hobbs

I did not go through the 804 data sheet but on other LPC I've used:
1 - minimum size is going to be 4K blocks
2 - everything is going to stall while the flash operation is in
progress, no interrupts, no nothing.
If you are going to do some type of self cal you need to run the cal,
gather the data and then do the write (well, erase and write).

If you are going to be updating the calibration table many many
times I think it's best to have a SPI or I2C eeprom or flash.


-- 
Chisolm
Republic of Texas

On 01/24/2019 10:25 AM, Phil Hobbs wrote:
> So we've got this custom product that includes a voltage-controlled 
> amplifier.
> 
> VCA chips as used in ultrasound and so on have nice low noise at the 
> highest gains, but at low gain they stink on ice.  The same is true of 
> all transconductance-based VCAs unless you use a zillion stages.
> 
> Sooo, we're faking it with a dpot, an op amp with a mux-controlled 
> resistor ladder, and an LPC804 Cortex M0+.
> 
> The resistor ladder is made out of standard-value Susumu 25-ppm 
> resistors, so it's better than the dpot except that the switchable gains 
> aren't exactly powers of two.
> 
> The simple way of handling this is to have the thing self-calibrate. 
> That could be done at power-up and the cal table kept in RAM, or at test 
> time with the table in flash.
> 
> There's some lore on the net that having the firmware write to the MCU 
> flash is a bad idea.
> 
> Experiences? Opinions?
> 
> Cheers
> 
> Phil Hobbs
> 
> 

No on-board EEPROM on those parts? Maybe 8 bit has a life after all. 
Even the 50 cent ATTiny85 has 512 bytes of 100k-cycle EEPROM on die it 
can come in very handy