Libmc1322x developers guide

Development to reduce RAM usage

Here is some ram usage information from the nvm_read program:

12272 nvm_read
10224 nvm_read without rom calls (2048 bytes)
8060  nmv_read without printf (2164)
3036  without uart_init (and all the uart related buffers etc.) (5024 bytes)

Eliminating or minimizing ROM_VARS space

There is currently a 1.7kB space reserved for the rom_vars. This area of RAM is allowed to be used by the various routines in the ROM. The space is reserved in the start.S:

.org 0x120
ROM_var_start: .word 0
.org 0x7ff
ROM_var_end: .word 0
#endif /*USE_ROM_VARS*/

Currently, the only critical functions performed by ROM calls are the nvm_* routines and there isn't a particular reason why these have to be ROM calls. get_lqi in maca.c is also a ROM call.

There are two approaches here:

• Isolate the RAM locations necessary for the ROM calls used and only reserve them.
• Re-implement the rom calls.

Neither option is particularly difficult. The largest RAM gains would probably come from isolating the rom_vars currently used (unless the ROM code is doing something bad like allocating big buffers).

Upgrading to the latest GCC

####Compiler link

https://sourcery.mentor.com/GNUToolchain/package11442/public/arm-none-eabi/arm-2013.05-23-arm-none-eabi-i686-pc-linux-gnu.tar.bz2

####From Tyler:

I think it works just fine.  Download the latest code sorcery compiler... turn off all the 'interworking'
 stuff in the makefile (interworking is default now)... leave the '-mthumb' thingy (ROM calls are thumb I 
guess)... and apply the 'Mar Fix' to start.S (to get into Thumb) and you are all set.

I have only experimented on an econotag.  I wrote a program (a libmc1322x test program) to play with the 
nvm_* routines.  I was able to detect/read/write/erase nvm.  I was able to get rftest-rx/tx to talk to one 
another.  Also, I was able to compile the backpack code and get it to boot up on an econotag.  I just 
haven't run anything on my own hardware.

####The "mar fix" to start.S:

The jump to main in start.S needs to become:

        ldr ip, main_addr
        bx ip

main_addr:
        .word main

Not sure if this code will still work on the old compiler (but I think it will).

There are various places where there are unused variables (e.g. i2c and maca). These need:

__attribute__((unused))

Then pwm.c has an error with the assembly unless the following is used:

-fno-strict-volatile-bitfields