RGBtoHDMI/src/rpi-aux.c

#include <stdio.h>
#include "rpi-aux.h"
#include "rpi-base.h"
#include "rpi-gpio.h"
#include "info.h"
#include "startup.h"
#include "stdlib.h"

/* Define the system clock frequency in MHz for the baud rate calculation.
   This is clearly defined on the BCM2835 datasheet errata page:
   http://elinux.org/BCM2835_datasheet_errata */
#define FALLBACK_SYS_FREQ    250000000

// #define USE_IRQ

#define TX_BUFFER_SIZE 65536  // Must be a power of 2

static aux_t* auxillary;

aux_t* RPI_GetAux(void)
{
   auxillary = (aux_t*) AUX_BASE;
   return auxillary;
}

#if defined(USE_IRQ)

#include "rpi-interrupts.h"

// Note, at the point the MiniUART is initialized, low vectors are in use
#define IRQ_VECTOR 0x38

static char *tx_buffer;
static volatile int tx_head;
static volatile int tx_tail;

static void __attribute__((interrupt("IRQ"))) RPI_AuxMiniUartIRQHandler() {
   auxillary = (aux_t*) AUX_BASE;
   while (1) {

      int iir = auxillary->MU_IIR;

      if (iir & AUX_MUIIR_INT_NOT_PENDING) {
         /* No more interrupts */
         break;
      }

      /* Handle RxReady interrupt */
      if (iir & AUX_MUIIR_INT_IS_RX) {
         /* Just echo characters */
         RPI_AuxMiniUartWrite(auxillary->MU_IO & 0xFF);
      }

      /* Handle TxEmpty interrupt */
      if (iir & AUX_MUIIR_INT_IS_TX) {
         if (tx_tail != tx_head) {
            /* Transmit the character */
            tx_tail = (tx_tail + 1) & (TX_BUFFER_SIZE - 1);
            auxillary->MU_IO = tx_buffer[tx_tail];
         } else {
            /* Disable TxEmpty interrupt */
            auxillary->MU_IER &= ~AUX_MUIER_TX_INT;
         }
      }
   }
}
#endif


void RPI_AuxMiniUartInit_With_Freq(int baud, int bits, int sys_freq)
{
   auxillary = (aux_t*) AUX_BASE;
   volatile int i;

   /* As this is a mini uart the configuration is complete! Now just
      enable the uart. Note from the documentation in section 2.1.1 of
      the ARM peripherals manual:

      If the enable bits are clear you will have no access to a
      peripheral. You can not even read or write the registers */
   auxillary->ENABLES = AUX_ENA_MINIUART;

   /* Disable flow control,enable transmitter and receiver! */
   auxillary->MU_CNTL = 0;

   /* Decide between seven or eight-bit mode */
   if (bits == 8)
      auxillary->MU_LCR = AUX_MULCR_8BIT_MODE;
   else
      auxillary->MU_LCR = 0;

   auxillary->MU_MCR = 0;

   /* Disable all interrupts from MU and clear the fifos */
   auxillary->MU_IER = 0;
   auxillary->MU_IIR = 0xC6;

   /* Transposed calculation from Section 2.2.1 of the ARM peripherals manual */
   auxillary->MU_BAUD = ( sys_freq / (8 * baud)) - 1;

#ifdef USE_IRQ
   tx_buffer = malloc(TX_BUFFER_SIZE);
   tx_head = tx_tail = 0;
   *((uint32_t *) IRQ_VECTOR) = (uint32_t) RPI_AuxMiniUartIRQHandler;
   RPI_GetIrqController()->Enable_IRQs_1 = (1 << 29);
   auxillary->MU_IER |= AUX_MUIER_RX_INT;
#endif

   /* Setup GPIO 14 and 15 as alternative function 5 which is
      UART 1 TXD/RXD. These need to be set before enabling the UART */
   RPI_SetGpioPinFunction(RPI_GPIO14, FS_ALT5);
   RPI_SetGpioPinFunction(RPI_GPIO15, FS_ALT5);

   // Enable weak pullups
   RPI_GpioBase->GPPUD = 2;
   // Note: the delay values are important, with 150 the receiver did not work!
   for (i = 0; i < 1000; i++)
   {
   }
   RPI_GpioBase->GPPUDCLK0 = (1 << 14) | (1 << 15);
   // Note: the delay values are important, with 150 the receiver did not work!
   for (i = 0; i < 1000; i++)
   {
   }
   RPI_GpioBase->GPPUDCLK0 = 0;

   /* Disable flow control,enable transmitter and receiver! */
   auxillary->MU_CNTL = AUX_MUCNTL_TX_ENABLE | AUX_MUCNTL_RX_ENABLE;
}

void RPI_AuxMiniUartInit(int baud, int bits)
{
   int sys_freq = get_clock_rate(CORE_CLK_ID);

   if (!sys_freq) {
      sys_freq = FALLBACK_SYS_FREQ;
   }
   RPI_AuxMiniUartInit_With_Freq(baud, bits, sys_freq);
};

void RPI_AuxMiniUartWrite(char c)
{
   auxillary = (aux_t*) AUX_BASE;
#ifdef USE_IRQ
   int tmp_head = (tx_head + 1) & (TX_BUFFER_SIZE - 1);

   /* Test if the buffer is full */
   if (tmp_head == tx_tail) {
      int cpsr = _get_cpsr();
      if (cpsr & 0x80) {
         /* IRQ disabled: drop the character to avoid deadlock */
         return;
      } else {
         /* IRQ enabled: wait for space in buffer */
         while (tmp_head == tx_tail) {
         }
      }
   }
   /* Buffer the character */
   tx_buffer[tmp_head] = c;
   tx_head = tmp_head;

   /* Enable TxEmpty interrupt */
   auxillary->MU_IER |= AUX_MUIER_TX_INT;
#else
   /* Wait until the UART has an empty space in the FIFO */
   while ((auxillary->MU_LSR & AUX_MULSR_TX_EMPTY) == 0)
   {
   }
   /* Write the character to the FIFO for transmission */
   auxillary->MU_IO = c;
#endif
}

void RPI_AuxMiniUartFlush() {
   auxillary = (aux_t*) AUX_BASE;
#ifdef USE_IRQ
   while (tx_tail != tx_head); // Currently untested!
#else
   /* Wait until the UART is Idle */
   while ((auxillary->MU_LSR & AUX_MULSR_TX_IDLE) == 0)
   {
   }
#endif
}