stm32f103rct6 with more ram then expected

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Some time ago, I boght a cheap devboard from a  well known Chinese  
webshop with a STM32F103RCT6 chip on it.

According to the datasheets, that chip has 48 KB of RAM and 256 KB of  

However, when using the linux arm-gdb and the st-util and st-info, they  
say that the chip actually has 64 KB of RAM (so more then exptected).

Using gdb (writing to memory and reading back from it), it does look at  
there is indeed 64 KB of RAM in the chip, ... but I do not find any  
reference to that chip with 64 KB of RAM.

Anybody any idea what is going on here?

The datasheet does mention this:
1. 64 KB RAM for 256 KB Flash are available on devices delivered in CSP  
packages only.

but the "T6" (at the end of full name) indicates that it is a  
LQFP64-package, no WLCSP64. (and, indeed, it is a LQFP chip).

Or does "CSP" mean something else? (Customer Special ???)

2/ Or could it be that this chip was originally intended as a ..."RD" or  
"RE" chip (384 or 512 KB of flash, 64 KB of RAM) where that the  
post-production quality-check showed that the upper half of the flash is  
bad, ...  so instead of just trowing it away, it is sold as a "RC" chip  
(256 KB of flash)?

3/ Or is this a counterfeit?

Did somebody already have simular experience?
Any ideas?

Cheerio! Kr. Bonne.

Re: stm32f103rct6 with more ram then expected
luni, 26 iunie 2017, 02:42:02 UTC+3, kristoff a scris:
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It might be a "GD" device.
Google "GD STM32" if you want to know more. I don't know details.

Re: stm32f103rct6 with more ram then expected
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It is clear that ST produces much less chip variants than they sell. However
you don't know what you get beside that what is promised by the original
data sheets. Are add-ons
- still availabe on the next chip you buy?
- where add-ons tested bad during production?
- where add-ons tested at all?

For a check F103xB vs F103xE, check for the presence of the additional
devices, like ADC3, FSMC, SDIO, TIM5, SPI2, UART4/5 etc.

Uwe Bonnes       

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
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Re: stm32f103rct6 with more ram then expected
Uwe Bonnes wrote on 6/26/2017 8:09 AM:
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I've wondered how MCU makers handle the *huge* proliferation of feature  
combinations.   The FPGA guys used to claim that was why they couldn't offer  
FPGAs with CPUs, the huge proliferation of part numbers (combos of FPGA  
size, memory size, CPU speed...) making all parts more expensive.  So how do  
the MCU guys do it?  Well, I guess that's how, they don't produce separate  
dies for each PN, they just test them for the features they are selling...  
just like the FPGA guys.


Rick C

Re: stm32f103rct6 with more ram then expected
Den mandag den 26. juni 2017 kl. 16.47.01 UTC+2 skrev rickman:
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many years ago I worked at place that was bitten by that,  
Someone had made an error and used a part of ram that was only there because  
the part were the same die as a bigger part.  

eventually volume got so big the manufacturer made a new smaller die,  
resulting in the code failing and production halting  


Re: stm32f103rct6 with more ram then expected
On Mon, 26 Jun 2017 10:46:59 -0400, rickman wrote:

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As an example of what the FPGA guys do, Xilinx's Zynq 7 family has ten  
members.  I'm fairly sure there are only six unique dies though.  I base  
this on things like features, configuration bitstream size, DC specs, etc.

XC7Z007S & XC7Z010 are the same
XC7Z012S & XC7Z015 are the same
XC7Z014S & XC7Z020 are the same
XC7Z035 & XC7Z045 are the same

The 'S' suffix parts have only one ARM core, which means one of the two  
ARM cores on the die has been disabled.  The parts already have  
(polysilicon?) efuses used for other purposes, so I assume they use a  
hidden set of fuses to disable features.
There would be no cost saving in removing an ARM core (as the die size  
would not change - it's a small area in the corner of the FPGA), but  
there could be a cost saving in not testing one of them.

The user guide says the FPGA fabric size is different, too (e.g. the '007  
supposedly has about 70% of the fabric of the '010) but this is merely a  
software limitation - if it knows the target device is a '007, it won't  
allow it to achieve more than 70% utilisation.


Re: stm32f103rct6 with more ram then expected
Allan Herriman wrote on 6/27/2017 7:23 AM:
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Certainly the smaller number of chip designs is an advantage when it costs  
millions of dollars to produce a new chip.  The costs the Xilinx guy was  
talking about was mostly the cost of dealing with a large proliferation of  
part numbers which is not addressed by using the same die for multiple  
device part numbers.

Part of the reason I think they have starting including CPUs on FPGAs today  
is that the CPUs are higher end types like the ones used in cell phones  
rather than lower end devices like common MCUs.  With MCUs you expect the  
memory to be on die or at lease in the package.  So that alone is a two or  
three or even four factor for part numbers.  The higher end CPUs are  
typically used with external memory relieving the FPGA maker of dealing with  
a range of memory sizes.


Rick C

Re: stm32f103rct6 with more ram then expected
Hi Kristoff,

yes, this is known:

Sometimes they come with more memory, and the additional memory should be fine,
at least in the cases I know of.

Same holds true for Lattice FPGAs:

iCE40 HX1K and HX8K are the dies, the HX4K is just an error free HX8K die within
a smaller package. Using Icestorm/Yosys/Arachne, you get the full HX8K capabilities.


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