Sanity Check: Considering my first SAM4L project. (And shaking in my boots.)

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Ok, you got me. I'm not wearing any boots.

 

The 1207 page datasheet is about enough to scare me back to xMega.

 

Design Goals :

  • Powered by 2 AA batteries and a TPS60100 regulator.
  • "Turns off" by going to sleep.
  • 320x240 TFT LCD display with quick drawing. The whole reason to consider SAM vs xMega.
  • Resistive touch screen.
  • 2 5 way "navigation" buttons. Use one of these to turn it on.
  • Micro SD card able to turn off by a PFET so it's not sucking amps while not used. It's "sleep" mode seems to be like a quarter milliamp. Used mainly for updating the software. Perhaps I should consider USB instead.
  • SPI flash chip for holding configuration and settings. There may be lots of nonvolatile data.
  • NRF24L01+ counterfeit for communication, 'cause it has to communicate with very cheap gadgets.
  • Measure the battery voltage.

 

Overall Design:

100 pin SAM4LS4CA-AU 'cause I kept running out of pins on the 64 pin xMega. So, what was I using ALL those pins for?

Use the SPI peripheral on PA21 through 24 for RF module and flash card

Use the SPI peripheral on PA27 through 30 for SD card so I can use RF module and Flash while SD card is turned off.

Use the 16 bit Port B for the 16 data lines to the display. 

Maybe use C++ instead of C because I won't need __flash or memx.

 

Misc Questions (things I haven't yet found in TFM):

  1. In power down BACKUP mode, only the EIC lines can wake it up? I only find these on PA function C, so my SPI pins aren't on PA? Perhaps you switch the mux pin by pin?
  2. Can the ADC read voltages up the VCC instead of VCC-0.6 like the xMega? If not, then how 'bout connecting the DAC to the touch screen so I can set the "full scale" voltage. Maybe through a pair of pfets so I can disconnect the pin while measuring it. Can DAC drive enough current? Touch screens seem to be 330 ohms the short way and 660 ohms the long way. Could put an amplifier, but then I'd have to be able to turn THAT off too.
  3. PA2 selects Buck or LDO converter and needs to be high (or low) on reset. I should just connect this pin high and leave it alone? It's not like I have a shortage of pins.
  4. Perhaps some experienced user would say, "na, you want to do it THIS way instead. Save you much grief"?

 

More questions are sure to arise.

 

 

The largest known prime number: 282589933-1

In my humble opinion, I'm always right. 

Last Edited: Thu. Oct 15, 2015 - 11:35 PM
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Just out of interest why SAM4 rather than SAM3? Do you need fast floating point/DSP-like capabilities?

 

Also what is the actual bottle-neck to the LCD anyway? Is it IO speed or speed of generating the pixels in the first place? (or perhaps just lack of addressable RAM for image buffers?)

 

Oh and when I look at 100 pin M3/M4 in Atmel's product selector I see 43 devices but when I add "SD/eMMC" (the 4 bit interface to SD instead of SPI) the number drops to 28 and that does not include SAM4LS4C ?

 

EDIT: think I just answered one of my own questions. If Atmel's selector is to be believed it's only SAM4 not SAM3 that offer Picopower - that seems astonishing if true!

Last Edited: Fri. Jul 17, 2015 - 03:39 PM
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Hmm. Maybe I'll look at SAM 3. Perhaps I could display graphics straight off the sd card.

 

I went to digikey, put in parameters and looked for chips and prices. Had to start somewhere.

 

I think picopower was new with SAM 4.

 

Still can't believe I was using up all 64 pins on the xMega192D3 part and wanted more.

 

 

The largest known prime number: 282589933-1

In my humble opinion, I'm always right. 

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Maybe because I can get SAM 4 in the TQFP pack that I know how to solder.

The largest known prime number: 282589933-1

In my humble opinion, I'm always right.