Flash Programming; How Does Flash Programming Via J-Link / J-Trace Work; Data Download To Ram; Data Download Via Dcc - Segger J-Link User Manual

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11.4 Flash programming

J-Link / J-Trace comes with a DLL, which allows - amongst other functionalities -
reading and writing RAM, CPU registers, starting and stopping the CPU, and setting
breakpoints. The standard DLL does not have API functions for flash programming.
However, the functionality offered can be used to program the flash. In that case, a
flashloader is required.

11.4.1 How does flash programming via J-Link / J-Trace work?

This requires extra code. This extra code typically downloads a program into the RAM
of the target system, which is able to erase and program the flash. This program is
called RAM code and "knows" how to program the flash; it contains an implementa-
tion of the flash programming algorithm for the particular flash. Different flash chips
have different programming algorithms; the programming algorithm also depends on
other things such as endianess of the target system and organization of the flash
memory (for example 1 * 8 bits, 1 * 16 bits, 2 * 16 bits or 32 bits). The RAM code
requires data to be programmed into the flash memory. There are 2 ways of supply-
ing this data: Data download to RAM or data download via DCC.

11.4.2 Data download to RAM

The data (or part of it) is downloaded to an other part of the RAM of the target sys-
tem. The Instruction pointer (R15) of the CPU is then set to the start address of the
Ram code, the CPU is started, executing the RAM code. The RAM code, which con-
tains the programming algorithm for the flash chip, copies the data into the flash
chip. The CPU is stopped after this. This process may have to be repeated until the
entire data is programmed into the flash.

11.4.3 Data download via DCC

In this case, the RAM code is started as described above before downloading any
data. The RAM code then communicates with the host computer (via DCC, JTAG and
J-Link / J-Trace), transferring data to the target. The RAM code then programs the
data into flash and waits for new data from the host. The WriteMemory functions of J-
Link / J-Trace are used to transfer the RAM code only, but not to transfer the data.
The CPU is started and stopped only once. Using DCC for communication is typically
faster than using WriteMemory for RAM download because the overhead is lower.

11.4.4 Available options for flash programming

There are different solutions available to program internal or external flashes con-
nected to ARM cores using J-Link / J-Trace. The different solutions have different
fields of application, but of course also some overlap.
11.4.4.1 J-Flash - Complete flash programming solution
J-Flash is a stand-alone Windows application, which can read / write data files and
program the flash in almost any ARM system. J-Flash requires an extra license from
SEGGER.
11.4.4.2 RDI flash loader: Allows flash download from any RDI-compliant
tool chain
RDI, (Remote debug interface) is a standard for "debug transfer agents" such as J-
Link. It allows using J-Link from any RDI compliant debugger. RDI by itself does not
include download to flash. To debug in flash, you need to somehow program your
application program (debuggee) into the flash. You can use J-Flash for this purpose,
use the flash loader supplied by the debugger company (if they supply a matching
flash loader) or use the flash loader integrated in the J-Link RDI software. The RDI
software as well as the RDI flash loader require licenses from SEGGER.
J-Link / J-Trace (UM08001)
CHAPTER 11
© 2004-2013 SEGGER Microcontroller GmbH & Co. KG
Background information