I feel like I missed the first day of class when some basic idea was taught that makes the world make sense. I just spent an entire day troubleshooting my UART code. When my project initializes the UART connection, it starts with no parity, then sends the +ICF command to change the modem's UART to an ODD parity. Then my UART quickly reconfigures to ODD parity and off we go, saving the world and whatnot. However, I was loosing all communications as soon as I told the modem to switch to ODD parity. It turned out to be a problem with how I was reconfiguring my UART to ODD parity. Here's how I was trying to do it:
UART_WriteControlRegister( (UART_ReadControlRegister() & ~UART_CNTRL_PARITY_TYPE_MASK) | UART__B_UART__ODD_REVB );
It never occurred to me that I might need to modify the ODD_REVB constant to set the correct bits. Finally, I noticed with debugging that the wrong bits were being set by this command so I looked up the #define for these constants in the header file. Here are the #defines:
/* Control Register definitions */
...
#define UART_CTRL_PARITY_TYPE0_SHIFT (0x03u) /* Defines the type of parity implemented */
#define UART_CTRL_PARITY_TYPE1_SHIFT (0x04u) /* Defines the type of parity implemented */
...
#define UART_CTRL_PARITY_TYPE_MASK (0x03u << UART_CTRL_PARITY_TYPE0_SHIFT)
...
/***************************************
* Enumerated Types and Parameters*
**************************************/
...
#define UART__B_UART__NONE_REVB 0
#define UART__B_UART__EVEN_REVB 1
#define UART__B_UART__ODD_REVB 2
#define UART__B_UART__MARK_SPACE_REVB 3
...
As you can see, the parity constant values are relative to the mask, whereas I expected them to be shifted to the correct position in the byte. So, after making the change below, everything works a whole lot better:
UART_WriteControlRegister( (UART_ReadControlRegister() & ~UART_CTRL_PARITY_TYPE_MASK) | (UART__B_UART__ODD_REVB << UART_CTRL_PARITY_TYPE0_SHIFT) );
I am not a classically trained programmer. When I define constants for addressing bits in a bitfield, I will "pre-shift" them in the #define. Is it more standard practice to do it the way this UART API is written? Hopefully, this will help anyone else who missed the first day of class to save themselves a concussion from beating their heads on their keyboards like I did.
