MIDI I/O with NXP LPC43xx micro controller (ARM Cortex M4 MCU)

MIDI_IO_LPC43xx.cpp

#define CMSIS_BITPOSITIONS
#include <__cross_studio_io.h>
#include "lpc43xx.h"


//
// Configure LPC43xx ARM Cortex M4 microcontroller to 204 MHz using 12 MHz crystal
// 

void Configure_Main_Clock_And_Busses()
{
    // Enable crystal oscillator
    LPC_CGU->XTAL_OSC_CTRL = 0;
    for (volatile uint32_t i = 0; i < 1000000; ++i);
 
    // Set the PLL to 204 MHz
    uint32_t control_register = LPC_CGU->PLL1_CTRL;
 
    control_register &= ~(CGU_PLL1_CTRL_MSEL_Msk | CGU_PLL1_CTRL_CLK_SEL_Msk | CGU_PLL1_CTRL_PD_Msk);
    control_register |= 16 << CGU_PLL1_CTRL_MSEL_Pos;                   // Feedback-divider division ratio = 17 ---> 17 * 12 MHz = 204 MHz
    control_register |= 6  << CGU_PLL1_CTRL_CLK_SEL_Pos;                // Clock source = crystal oscillator

    LPC_CGU->PLL1_CTRL = control_register;
    while (!(LPC_CGU->PLL1_STAT & CGU_PLL1_STAT_LOCK_Msk));

    // Set M4 clock to PLL1
    LPC_CGU->BASE_M4_CLK = 9 << CGU_BASE_M4_CLK_CLK_SEL_Pos |           // Clock source = PLL1
                           1 << CGU_BASE_M4_CLK_AUTOBLOCK_Pos;          // Block clock automatically during frequency change

    // Set PERIPH clock to PLL1
    LPC_CGU->BASE_PERIPH_CLK = 9 << CGU_BASE_PERIPH_CLK_CLK_SEL_Pos |   // Clock source = PLL1
                               1 << CGU_BASE_PERIPH_CLK_AUTOBLOCK_Pos;  // Block clock automatically during frequency change

    // Set APB1 clock to PLL1
    LPC_CGU->BASE_APB1_CLK = 9 << CGU_BASE_APB1_CLK_CLK_SEL_Pos |       // Clock source = PLL1
                             1 << CGU_BASE_APB1_CLK_AUTOBLOCK_Pos;      // Block clock automatically during frequency change

    // Set APB3 clock to PLL1
    LPC_CGU->BASE_APB3_CLK = 9 << CGU_BASE_APB3_CLK_CLK_SEL_Pos |       // Clock source = PLL1
                             1 << CGU_BASE_APB3_CLK_AUTOBLOCK_Pos;      // Block clock automatically during frequency change
}


/*
    Use UART1 input & output for MIDI.
    Pin P1_13 = MIDI output
    Pin P1_14 = MIDI input

    ------------

    Crystal        = 12 MHz
    MIDI baud rate = 31250
    12 MHz / 31250 = 384 cycles per baud

    UART is always 16x oversampling.
*/

void Configure_MIDI_IO()
{
    // Set UART1 clock to crystal
    LPC_CGU->BASE_UART1_CLK |= 6 << CGU_BASE_UART1_CLK_CLK_SEL_Pos |        // UART1 clock source = Crystal
                               1 << CGU_BASE_UART1_CLK_AUTOBLOCK_Pos;       // Block clock automatically during frequency change

    // MIDI format = 31250 baud, 1 start bit, 8 data, no parity, 1 stop bit
    LPC_UART1->LCR |= 3 << UART1_LCR_WLS_Pos |                              // 8bit character length
                      UART1_LCR_DLAB_Msk;                                   // Enable Divisor Latch Access

    LPC_UART1->DLL &= ~UART1_DLL_DLLSB_Msk;
    LPC_UART1->DLL |= 24 << UART1_DLL_DLLSB_Pos;                            // 12MHz clock, 31250 baud, 16x oversampling ---> 12MHz / (16 * 31250) = 24
    LPC_UART1->LCR &= ~UART1_LCR_DLAB_Msk;                                  // Disable Divisor Latch Access

    LPC_UART1->FCR |= UART1_FCR_FIFOEN_Msk;                                 // Enable FIFO

    // Set pin functionalities
    LPC_SCU->SFSP1_13 |= 1 << SCU_SFSP1_13_MODE_Pos;                        // P1_13 = FUNC1 = UART1 TXD = MIDI-OUT-1
    LPC_SCU->SFSP1_14 |= 1 << SCU_SFSP1_14_MODE_Pos;                        // P1_14 = FUNC1 = UART1 RXD = MIDI-IN-1
    LPC_SCU->SFSP1_14 |= SCU_SFSP1_14_EZI_Msk;                              // P1_14 = Enable input buffer

}


void Send_MIDI_Message(uint32_t message_24bit)
{
    while (!(LPC_UART1->LSR & UART1_LSR_THRE_Msk));         // Wait until UART1 THR is empty
    LPC_UART1->THR = (message_24bit >> 16) & 0xFF;

    while (!(LPC_UART1->LSR & UART1_LSR_THRE_Msk));
    LPC_UART1->THR = (message_24bit >> 8) & 0xFF;

    while (!(LPC_UART1->LSR & UART1_LSR_THRE_Msk));
    LPC_UART1->THR = message_24bit & 0xFF;
}


void main(void)
{
    Configure_Main_Clock_And_Busses();
    Configure_MIDI_IO();

    // MIDI input test
    while (1)
    {
        if (LPC_UART1->LSR & UART1_LSR_RDR_Msk)
            debug_printf("%x ", LPC_UART1->RBR & 0xFF);
    }
/*
    // MIDI output test
    while (1)
    {
        Send_MIDI_Message(0x0090017F);      // Note on
        for (volatile uint32_t i = 0; i < 4000000; ++i);

        Send_MIDI_Message(0x00900100);      // Note off
        for (volatile uint32_t i = 0; i < 8000000; ++i);
    }
*/
}

This example uses NXP LPC4330FBD144 microcontroller.
It's should be usable with other LPC43xx microcontrollers with minimal changes.