project sd-card with ccs c compiler

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SD-Card with CCS C CompilerDescriptionHardwareSoftwareLinks

Description

This project shows how to use a SD-Card with FAT16 file system. It is based on the example MMC/SD-Card driver

(mmcsd.c) and FAT file system driver (fat.c) delivered with the CCS C compiler.

Unfortunately, the example didn't work properly for me. So I searched the web and found some required changes to

make it work. All modifications are described in the following article.

Hardware

SD-cards can be interfaced to a microcontroller via SPI-Bus, hence only 4 I/O pins (SDI, SDO, SCK, CS) are required to

connect the SD-card to the PIC.

SD-cards operate at 2.7V .. 3.6V while the 18F PICs usually operate at 5V. Hence a voltage level translation is required

for the SD-card inpus (SDI, SCK, CS). There are a lot of examples available in the web where a voltage divider with

resistors is used to translate the 5V signals to 3.3V. This will work, but at higher SPI speeds this might cause problems.

Due to that, I used a 74AC125 buffer to do the level translation which works more reliable than the voltage divider.

SD-Card Module

Here the schematic of the SD-Card module with the voltage level translation. The pins on the connector SV1 need to be

connected to the microcontroller pins.

Important: SDO and SDI are the pin names from the SD-card point of view, i.e. SDO needs to be connected to SDI on

the microcontroller and SDI needs to be connected to SDO in the microcontroller!

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picprojects.net | SD-Card with CCS C Compiler http://www.picprojects.net/sdcard_demo/index.html

1 of 4 3/17/2015 4:07 PM

Here some pictures of the SD-card module which I have build on a breadboard and the experimental setup. I used the

PIC1618Exp-28d experiment board assembled with a PIC18F2620 for the experimental setup.

Software

As mentioned in the description for this article, I used the ex_fat.c example which is delivered with the CCS C compiler.

Unforunately, when I run the demo and created some files with the demo, I was not able to see the files when I pluged

the SD-card into my PC. After some investigations I found a solution for this problem in the CCS forum which I will

summarize here.

Modifications in mmcsd.c

Search for

uint32_t g_mmcsdBufferAddress;and add under it:

uint32_t g_mmcsdPartitionOffset;Next, just before the "mmcsd_init" function add a new function:

void mmcsd_check_part(uint16_t off){if (g_mmcsd_buffer[off + 0] == 0x80){// active partition


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uint8_t t;t = g_mmcsd_buffer[off + 4];if (t == 0x04 || t == 0x06 || t == 0x0B){// FAT16 or FAT32 partition g_mmcsdPartitionOffset = make32(g_mmcsd_buffer[off + 11], g_mmcsd_buffer[off + 10],g_mmcsd_buffer[off + 9], g_mmcsd_buffer[off + 8]) * MMCSD_MAX_BLOCK_SIZE;}}}

In the "mmcsd_init" function, right after the line:

r1 = mmcsd_load_buffer();Add the lines:

g_mmcsdPartitionOffset = 0;mmcsd_check_part(0x1EE);mmcsd_check_part(0x1DE);mmcsd_check_part(0x1CE);mmcsd_check_part(0x1BE);

Finally, in the function "mmcsd_move_buffer", after the line:

new_block = new_addr - (new_addr % MMCSD_MAX_BLOCK_SIZE);Add the line:

new_block += g_mmcsdPartitionOffset;

Modifications in mmcsd.c

The CCS "fat.c" functions "get_next_addr" and "get_prev_addr" do not correctly handle cluster transitions. The following

are corrected functions, so replace the function with the following code:

signed int get_next_addr(int32* my_addr){int32 temp;#ifdef FAT32int32 c;#elseint16 c;#endif// check to make sure that the next iteration will give us a contiguous address temp = *my_addr + 1;if((temp > Data_Start) && ((temp - Data_Start) % Bytes_Per_Cluster == 0)){// convert the current address into the address of where information about // the address is stored in the FAT, and put this value into the current address c = addr_to_cluster(temp - 1);if(get_next_cluster(&c) == EOF)return EOF;if (c >=#ifdef FAT320x0FFFFFF8#else0xFFF8#endif)return EOF;temp = cluster_to_addr(c);}*my_addr = temp;return GOODEC;}

Further, get_prev_addr() needs to be updated:

signed int8 get_prev_addr(int32* my_addr){int32 temp;#ifdef FAT32int32 c;#elseint16 c;#endiftemp = *my_addr;// if we're trying to go backwards one entry from the beginning of the root, // we won't be able to... if(temp = Data_Start) && ((temp - Data_Start) % Bytes_Per_Cluster == 0)){c = addr_to_cluster(temp);if(get_prev_cluster(&c) == EOF)return EOF;temp = cluster_to_addr(c) + Bytes_Per_Cluster;}*my_addr = temp - 1;return GOODEC;}


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In fat_init() function search for the following lines

#ifdef FAT32Data_Start = Bytes_Per_Cluster + Root_Dir;#else // FAT16

and replace it with the following code (i.e. remove "Bytes_Per_Cluster +"):

#ifdef FAT32Data_Start = Root_Dir;#else // FAT16

And finally, get_short_file_name() needs to be replaced with the following code:

signed int get_short_file_name(int32 file_entry_addr, char sname[], int8 type){intbuf,i,j = 0;// one short file name has, at the most, 11 characters for(i = 0; i < 11; ++i){// read in a character if(mmcsd_read_data(i + file_entry_addr, 1, &buf) != GOODEC)return EOF;// convert the character if(buf != ' '){if (i == 8 && type != 0x10) sname[j++] = '.';sname[j++] = tolower(buf);}}if (sname[j - 1] == '.') --j;sname[j] = '\0';return GOODEC;}

With this modifications everything worked fine. But currently, the changes have only been verifed with FAT16 enabled,

i.e. I have enabled FAT16 support and disabled FAT32 in fat.c:

/// Define your FAT type here ///#define FAT16//#define FAT32

Links

Here some usefull links:

http://www.ccsinfo.com/forum/viewtopic.php?t=43402: CCS SD/MMC driver MBR supporthttp://www.ccsinfo.com/forum/viewtopic.php?t=43417: CCS FAT driver bugfix!

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project sd-card with ccs c compiler

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