LPC1768 SPI Test Mode

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by ddink on Tue Nov 19 09:21:07 MST 2013

I need a continious SPI clock in master mode (running all the time, even if there's nothing  to send) for testing purposes. I like to generate this by using the SPI test mode. Therefore I added SPTCR to the LP17xx.h Cmsis library:
typedef struct
  __IO uint32_t SPCR;
  __I  uint32_t SPSR;
  __IO uint32_t SPDR;
  __IO uint32_t SPCCR;
  __IO uint32_t SPTCR;
       uint32_t RESERVED0[2];
  __IO uint32_t SPINT;
} LPC_SPI_TypeDef;

then I added

to the runtime code (after the SPI was initialized).
In the disassembly it looks as following:
 23e:f04f 0300 mov.wr3, #0
242:f2c4 0302 movtr3, #16386; 0x4002
246:f04f 02fe mov.wr2, #254; 0xfe
24a:611a      strr2, [r3, #16]

All good so far, but when I run the program and read the SPTCR register, it is empty. There is also no cont. clock on the SPI Clk pin.
Are there any restritions for the testing mode or am I doing anythin wrong?

Thank you very much!