(Yet) More on the iPhone – How many ARM cores?
Back on July 6, Peter Clarke at EETimes Europe posed a fun question – how many ARM cores are there in the iPhone? Like many people, I’ve been following the multiple iPhone discussions, and his piece “IPhone teardowns fail to answer the 'ARM question'” caught my attention.
The initial assessment was three – an ARM 1176 in the Samsung applications processor, an ARM9 or 7 in the Marvell 88W8686 WLAN chip, and an ARM926 in the Infineon S-Gold2 baseband controller. There is also speculation that the PowerVR MBX 3D graphics processor is in the app’s processor, also licensed from ARM; and the CSR Bluetooth chip likely has an ARM MCU core in there, bringing the total up to five.
A few days ago I was poking around our teardown of the iPhone, and looking at the touchscreen module, with four chips on it:
iPhone touchscreen module
On the right half of the image, the Apple-branded chip is the Broadcom BCM5973A chip, and on the left half is a Philips (NXP) LPC2221. The NXP one caught my eye, since they have a LPC2220, which is a 16/32-bit ARM7TDMI-S CPU-based microcontroller. Part numbers can be deceptive, so we decapsulated the part, and found this:
Die photo of NXP LPC2221
And lo and behold, with this die marking:
LPC2221 die marking
Which solves that particular mystery – we have another ARM core in the iPhone. Of course that leaves the question, if the NXP chip is the touchscreen controller, what is the Broadcom chip?
During their Q2 call a couple of weeks ago, they specifically referred to the part as a touchscreen controller (my italics);
“On the mobile multimedia front, a decline of our traditional portable device end market revenue was more than offset by initial shipments of the new product with new functions into a recently announced hot new cellular handset. As illustrated by numerous publicly available teardowns, the new touch screen controller demonstrates our ability to create innovative devices for our most cutting edge customers.”
Other teardowns refer to it as an I/O controller. If the touchscreen is a capacitive sensor, then that makes sense – a device is needed to translate the variations in capacity and position into digital data suitable for the LPC2221. That actually ties in with the die photo (below), since it is laid out in the sort of regular array we would expect for an I/O part.
The ‘59’ prefix to the part number is a bit confusing, since the only 59*** parts on their website are power management units (BCM59000 series), and I believe those are fabbed by AMIS. This sort of product would be in the AMIS product range, though, so maybe the ‘59’ means “fabbed by AMIS”. Pure speculation, I know..
There certainly does not seem to be any large logic block on it such as an ARM CPU, anyway. And strangely, the copyright date on the chip is 2004, so either Broadcom has been in the iPhone design loop for a long time, or maybe this is an older part re-engineered to suit Apple’s requirements – another way of keeping costs down (iSuppli estimated its cost at $1.15).
Die photo of Broadcom BCM5973A chip
Copyright mark on BCM5973A
So depending on what you mean by “touchscreen controller”, it’s the Broadcom chip, the NXP chip, or looked at as a whole, the entire module – presumably the other two parts control the power environment for the MCU and the I/O chips.
Anyway, getting back to Peter Clarke’s question – the ARM count is up to six, which with the Wolfson audio codec, gives the UK a good chunk of the IP in the iPhone!
Don't forget to click on the thumbnails to bring up the full images!