Saturday, August 7, 2010

Arduino/AVR vs Cypress/PSOC

I've recently been working on a simple PSOC ( project using the CY8C64315 USB chip and can't help but compare it to the popular Arduino platform since it is pretty similar to the AVR 328P. These are my observations:

Feature Comparison

Cypress/PSOC 9, Arduino/AVR 5

Initially I chose PSOC because it has some great features packed into a tiny 16 pin QFN part at a cheap price. In particular it provides a full-speed USB device with very few external components -- not even a crystal! It runs at 24Mhz instead of the AVR's 20mhz and contains SPI, I2C, a bunch of IOs and so forth.

One issue is that it does not contain a serial UART (but other, bigger PSOC parts do), but I'm hoping to do a soft-serial implementation.

Perhaps its kind of silly but I didn't want my USB controller to be larger, more expensive, and have more pins than an embedded CPU itself (but when you get right down to it, it is in fact on par or more powerful than the 328p)! So the tiny part size combined with good features was the clincher for me.


Cypress/PSOC 3, Arduino/AVR 10

The Cypress Application Note search tool is totally impossible to use. And their community site is better but not "alive" like the Arduino or even avrfreaks. Its too tightly coupled with Cypress I think.

And none of this stuff comes up in google searches.

Note to Cypress -- you are NOT a SEARCH company! Just post all your App Notes in HTML form on a public site and let Google do the job. It will do it much better and you'll save some money.

One wild/good thing; I posted an issue bringing the chip up and actually got an essentially unsolicited telephone call from a real human being engineer the next day to help me (but had already figured it out). So that can make up for a lot of doc issues, but of course its pretty expensive for Cypress...

Hardware Design

Cypress 2, AVR 10

2. Application Schematic? It seems that Cypress didn't bother to put one in the datasheet. In fact I had to glean portions of the full "typical application schematic" from a bunch of "Application Notes" -- USB from here, ISSP from there. And of course those schematics were not necessarily for the chip variant I chose so there was lots of uncertainty in this process.

In contrast the Arduino project and all its variants are open hardware, so there are lots of circuit examples to choose from.

PSOC Designer vs Arduino IDE

Cypress 5, Arduno 5

PSOC is supposed to be some reconfigurable hardware "magic" that requires a fancy windows-only IDE. Not in my chip. Everything is just registers AFAIK. But still you can use a GUI to configure things and then it generates the code to write these registers for you. Now, this might seem cool, but actually it just gets in the way. It gives Cypress and excuse to not supply an API like the Arduino's "pinMode" and not to supply good docs. So what if you want to CHANGE the behavior of a pin while your program runs -- you've got to delve into the registers...

The rest of the IDE is everything you'd expect from a programmer's IDE. Good job Cypress! You are just as good as the free Eclipse :-).

However I do have one or 2 beefs. It:
1. Only runs on windows *sigh*
2. Pops up an irritiating "Programming" dialog box. This should be done in a small side-docked pane so the programmer can continue to WORK while the chip gets programmed...

Build Toolchain

Cypress/PSOC 5, Arduino/AVR 5

G++, GCC???

For some reason, instead of adding a gcc backend for the PSOC CPU, Cypress decided to go with some commercial C compiler. So no C++.

The result is a bit more like "Kiel" C then gcc and in particular has irritatingly difficult tranlation between a string stored in "flash" vs one in "ram". In fact, you have to define 2 functions one to handle "__flash" strings and one to handle normal "char *". *sigh*

But of course Arduino has this strange thing called "processing" with is actually C++ with some "try to help me but actually get in the way" thrown in so really average marks on both.

How to "Blink" (Basic programs/sketches)

Cypress/PSOC 7, Arduino/AVR 10

Its pretty INSANELY hard to figure out how to do simple things like configure a digital input (you use the GUI to graphically set the pin as CPU open-drain, then in code write the bit HIGH). Also standard C functions like "printf" are there but don't work... better that they not be there if they don't work.

Yet at the same time, it can be very EASY to do an entire USB HID device. So it just depends on how many Cypress libraries you can use.

Software Layers

Cypress/PSOC 9, Arduino/AVR 9

Ok, I've got to give cred to Cypress for being the 1st hardware company (AFAIK) to realise that we don't want to program at the register level. Yes, the GUI has "user modules" and you just pull them into your project to get massive functionality like a USB endpoint.

One nasty issue the use of lots of assembly??!!? All the Cypress libraries AFAIK are written in assembly. This makes reading the code hard :-). And also you can't ignore it; installing things like interrupt handlers requires you to get down in there and call out to your C. And this is NOT easy; to make the C compiler correctly save state, you have to basically trick the CPU into calling your C routine as if it was an interrupt even though you are already IN an interrupt. There's an entire App Note about how to do it :-(.

The advantage is probably smaller code sizes. But the cost is essentially that if you need to modify the library or add a feature, you have to either rewrite the whole thing yourself in C, or learn PSOC assembly which of course ties you and your work inseparably to this processor.


Its a neat little device with lots of potential. Great hardware, great software/support philosophy but not so good implementation. But its a pretty steep learning curve...

Now, Arduino/AVR generally relies on the community to provide great programming libraries, examples, tutorials and general help. And we do.

Cypress seems to be doing all/most of the work on its own. It seems to be caught attempting to implement a modern philosophy with a traditional unidirectional information-flow structure.

So while I give cred to Cypress for the tremendous effort I'm amazed at its total disregard for the open source movement -- in compilers, in IDE, in software libraries.

And I'm surprised at its inability to truly capitalize on internet resources and community.