AT91 Basic Boot project for AT91RM9200DK

 
 
 

 

Introduction

The goal of this demonstration project is to supply a simple solution to realize properly with efficiency a basic boot for your future application on the AT91RM9200.  Mainly, it initialises the power management controller, the SDRAM and the AT49BV1614 Flash, the different stacks, the exception vectors and finally C variables. This program also invokes the AT91 library V3.

Running the application

This application is linked in order to be loaded and run:

·         Either totally in SRAM:  Code and Data linked in 0x200000 for a debug use.

·          Or for your future boot program in ROM or Flash: Code linked in 0x0 and data in 0x200000.

This very small application (lower than 5 kb) sends through the DBGU serial port (115.2Kbps, 8 data bits, no parity, 1 stop bit, no flux control), messages corresponding to the correct execution of the code but be careful, not necessarily a good initialisation of the Power Management Controller, SDRAM or Flash memory (cf. Description).

Description

The program is simple: it just writes AT91F_LowLevelInit() Complete! and BasicBoot successful:  Enter main() through the DBGU serial port after the basic initialisations completed. This is the start-point to write a more complex application running on an AT91RM9200 but with a correct behaviour of the Power Management, Flash memory and SDRAM.

The start-up of this application is divided in two files: one in assembly (cstartup_xxx.s) and one in C (init_xxx.c). Assembly code tends to be as small as possible and thus calls C functions as soon as possible.

cstartup_xxx.s

init.c

The initialisation sequence is:

  • Definition of the Area Stack
  • Definition of the exception vectors
  • Enable the main oscillator Step 1.
  • Initialise stacks
  • Call AT91F_LowLevelInit()

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

·         Configure Coprocessor Register cp15.

·         Initialise C variables

·          Branch on the function main(): send a second string “BasicBoot successful:  Enter main() ” on the DBGU: AT91F_DBGU_Printk used.

 

 

 

 

 

AT91F_LowLevelInit():

  • Check the Main Oscillator Frequency (optional) Step 2.  AT91F_WaitForMainClockFrequency used.
  • Launch AT91F_InitFlash:
    • Initialise EBI for Static Memory Controller on Chip Select 0.
    • Flash configuration.
  • Launch AT91F_InitClocks (Step 3. to 5.).
    • Check if Input & Output Frequencies are in the correct PLL ranges (optional): AT91F_CheckPLL_FrequencyRange used.
    • Set PLLA and Divider A Step 3.
    • Set PLLB and Divider B Step 4.
    • Select Master Clock (and Processor Clock in consequence thanks to Master Clock Division MDIV field in MCKR) : Step 5.
  • Launch AT91F_Init SDRAM:
    • Configure PIOC as peripheral for D16 to D31.
    • Initialise EBI for SDRAM Controller on Chip Select 1.
    • SDRAM Initialisation procedure.  

(Following can be done later in the main application)

  • Open PIO for DBGU: AT91F_DBGU_CfgPIO used.
  • Configure DBGU: AT91F_US_Configure used.
  • Enable Transmitter: AT91F_US_EnableTx used.
  • Send a first string “AT91F_LowLevelInit() Complete!” on the DBGU: AT91F_DBGU_Printk used.

 

 

 

In a debug use:

·         The display on the DGBU of the two sentences indicates only a good execution of the code, but not necessarily a correct initialisation of the Power Management. Indeed, for example, if a frequency out of the PLL range is written, the AT91F_CheckPLL_FrequencyRange function will abort the AT91F_InitClocks execution and so the PLL and Master/Processor Clock chosen will not be programmed. So, this test should be deleted in case of a boot program execution on ROM.

·         After a reset, Slow Clock is normally selected. But in case of a boot already started (so in a full SRAM execution) and in order to be in a “reset situation”, Slow Clock is selected. This operation is effectuated in two steps because of constraints on the Master Clock selection sequence. (Cf. cstartup_ads.s Step 0a.). Finally, PLLs are turned off: Step 0b. (same situation for Step5 in init_ram.c)

Stacks are defined in cstartup_xxx.s. Stacks’ size corresponds to predefines set in the project. Cstartup_xxx.s must be placed at the beginning of the image.

Source files

./init_xxx.c

Includes low level functions definitions

./main.c

This is the application

./bin_xxx/cstartup_xxx.s

Cstartup

Related Documents

External Bus Interface Datasheet: 1759B.pdf

Static Memory Controller 2 Datasheet: 1783A.pdf

SDRAM Controller Datasheet: 1758B.pdf

Advanced Power Management Controller Datasheet: 2637A.pdf

Synchronous DRAM Micron: 128MSDRAM_E.pdf

ATMEL 16-megabit Flash Memory AT49BV1614: doc1411.pdf