External Memory (SRAM)

Macros
#define	XMEM_3KB   0
#define	MEM_OFFSET   0x1800u
#define	XMEM_SIZE   0x0800u

Functions
int	xmem_init (void)
	Initializes external SRAM (2KB or 3KB depending on XMEM_3KB).
int	SRAM_test (void)
	Tests external SRAM and prints a report.

Detailed Description

Macro Definition Documentation

MEM_OFFSET

#define MEM_OFFSET   0x1800u

#include <xmem.h>

Base address for external SRAM

Definition at line 26 of file xmem.h.

Referenced by SRAM_test().

XMEM_3KB

#define XMEM_3KB   0

#include <xmem.h>

Set to 1 if using 3KB memory instead of 2KB

Definition at line 15 of file xmem.h.

XMEM_SIZE

#define XMEM_SIZE   0x0800u

#include <xmem.h>

Size of external SRAM: 2KB

Definition at line 27 of file xmem.h.

Referenced by SRAM_test().

Function Documentation

SRAM_test()

int SRAM_test

(

void

)

#include <xmem.h>

Tests external SRAM and prints a report.

Returns

0 if memory is OK

-1 if write phase failed

-2 if retrieval phase failed

Definition at line 43 of file xmem.c.

                    {
  int status = 0;
 
  volatile uint8_t *ext_ram = (uint8_t *)MEM_OFFSET; // Start adress for SRAM
  const uint16_t ext_ram_size = XMEM_SIZE;
 
  uint16_t write_errors = 0;
  uint16_t retrieval_errors = 0;
 
  LOG_INF("Starting SRAM test...");
 
  // rand() stores internal state; use it once to vary the seed each run
  uint16_t seed = (uint16_t)rand();
 
  // Write phase: write and verify immediately
  srand(seed);
  for (uint16_t i = 0; i < ext_ram_size; i++) {
    uint8_t value = (uint8_t)rand();
    ext_ram[i] = value;
    uint8_t retrieved = ext_ram[i];
    if (retrieved != value) {
      // printf("Write phase error: ext_ram[%4u] = 0x%02X (should be
      // 0x%02X)\n\r",
      //        i, (unsigned)retrieved, (unsigned)value);
      write_errors++;
    }
  }
 
  // Retrieval phase: ensure values didn't change after writes
  srand(seed); // reset PRNG to same sequence
  for (uint16_t i = 0; i < ext_ram_size; i++) {
    uint8_t value = (uint8_t)rand();
    uint8_t retrieved = ext_ram[i];
    if (retrieved != value) {
      // printf(
      //     "Retrieval phase error: ext_ram[%4u] = 0x%02X (should be
      //     0x%02X)\n\r", i, (unsigned)retrieved, (unsigned)value);
      retrieval_errors++;
    }
  }
 
  LOG_INF("SRAM test completed");
 
  // printf(
  //     "SRAM test completed with\n\r%4u errors in write phase and\n\r%4u
  //     errors " "in retrieval phase\n\r\n\r", write_errors, retrieval_errors);
 
  if (write_errors) {
    return -1;
  }
  if (retrieval_errors) {
    return -2;
  }
 
  return 0;
}

Referenced by main().

xmem_init()

int xmem_init

(

void

)

#include <xmem.h>

Initializes external SRAM (2KB or 3KB depending on XMEM_3KB).

Returns

0 on success, non-zero on error

Definition at line 12 of file xmem.c.

                    {
  // SpecialFunction IO Register
  // Enable external memory interface, datasheet ATmega162 pg18 & 26
  MCUCR |= (1 << SRE);
 
  // Release pins used for JTAG
  // The pins in range PC7-PC4 is reserved for JTAG, and XMBK to stop pins from
  // floating see pg32 datasheet
  // SFIOR =
  //     (SFIOR & ~((1 << XMM1) | (1 << XMM0))) | ((1 << XMM2) /* | (1 <<
  //     XMBK)*/);
  SFIOR |= (1 << XMM2);
 
  // Extended MCU Control Register pg30 datasheet
  // Setting SRL2-SRL0 as 1 gives the sectors lower sector= 0x1100-0xDFFF & high
  // sector =0xE000-=xFFFF Setting SRW01 & SRW00 as 1 gives waitstate 2 cycles
  // before writing and 1 cycle before sending new address, see pg 31
  // EMCUCR =
  //     (1 << SRW01) | (1 << SRW00) & ~(1 << SRL2) & ~(1 << SRL1)6(1 << SRL0);
 
  // EMCUCR = (1 << SRW11 | 1 << SRW10) & ~(SRL0) & ~(SRL1) & ~(SRL2);
  // EMCUCR = 0;
 
  // MCU Control Register pg30
  // Same as EMCUCR but for upper sector, set to wait 1 cycle for read & write,
  // see table at pg31
  // MCUCR = (MCUCR & ~(1 << SRW11)) | (1 << SRW10);
  return 0;
}

Referenced by main().