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Bug in SPI setup for dsPIC?

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icefield

Joined: 09 May 2005
Posts: 20
Location: Canada

Bug in SPI setup for dsPIC?

Posted: Tue Sep 07, 2010 4:39 pm

Is it my imagination, or is there a bug in the compiler (4.112)? The snippet below compiles as shown below...

Code:

#include <33FJ256GP506.h>

#use delay(clock=20000000)

void main()
{
setup_spi(SPI_SLAVE | SPI_H_TO_L | SPI_SS_DISABLED);
setup_spi(SPI_SLAVE | SPI_H_TO_L | SPI_SS_ENABLED);
setup_spi(SPI_SLAVE | SPI_SS_ENABLED);
setup_spi(SPI_SLAVE | SPI_SS_DISABLED);

}

Bit 7 of SPI1CON1 is the SSEN bit, but the compiler seems to be inverting the sense of the bit. The relevant defines in 33FJ256GP506.h are correct, but the compiler is not simply OR'ing the flags together and loading the value into SPI1CON1 (as I would expect).

Note also that bit 8 (CKE) is getting set when all I asked for was bit 6 (CKP) to be set. CKP=1 with CKE=0 is a valid SPI mode, but there does not seem to be a way to achieve this because the compiler is "thinking"

Code:

From 33FJ256GP506.h:
#define SPI_SS_ENABLED 0x0080
#define SPI_SS_DISABLED 0x0000
#define SPI_SCK_IDLE_HIGH 0x0040
#define SPI_H_TO_L SPI_SCK_IDLE_HIGH

Resultant ASM:
.................... setup_spi(SPI_SLAVE | SPI_H_TO_L | SPI_SS_DISABLED);
00212: BCLR.B 240.6
00214: MOV #1C0,W4 <- bit 7 set (SSEN enabled, not disabled) - also bit 8 set???
00216: MOV W4,242
00218: BSET.B 241.7
.................... setup_spi(SPI_SLAVE | SPI_H_TO_L | SPI_SS_ENABLED);
0021A: BCLR.B 240.6
0021C: MOV #140,W4 <- bit 7 clear (SSEN disabled, not enabled) - also bit 8 set???
0021E: MOV W4,242
00220: BSET.B 241.7
.................... setup_spi(SPI_SLAVE | SPI_SS_ENABLED);
00222: BCLR.B 240.6
00224: CLR 242 <- bit 7 clear (SSEN disabled, not enabled)
00226: BSET.B 241.7
.................... setup_spi(SPI_SLAVE | SPI_SS_DISABLED);
00228: BCLR.B 241.7

icefield

Joined: 09 May 2005
Posts: 20
Location: Canada

Posted: Tue Sep 07, 2010 4:52 pm

Oh, I forgot. The last line:

Code:

setup_spi(SPI_SLAVE | SPI_SS_DISABLED);

actually disables the SPI, which is NOT what I asked for. It is possible to use the SPI bus in slave mode without SS (synchronization can come from some other hardware source). But there is no #define for SPI_DISABLE. Again, the compiler is "thinking" - if the user asks for a 0x0000 setup word, they must want the SPI disabled. Hmmm.

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