#ifndef _USART_H_
#define _USART_H_
#include <inttypes.h>
#include <util.h>

/* Transmit procedure:
 * 1.  Enable the USART by writing the UE bit in USART_CR1 register to 1.
 *
 * 2.  Program the M bit in USART_CR1 to define the word length.
 *
 * 3.  Program the number of stop bits in USART_CR2.
 *
 * 4.  Select DMA enable (DMAT) in USART_CR3 if Multi buffer Communication is
 *     to take place. Configure the DMA register as explained in multibuffer
 *     communication.
 *
 * 5.  Select the desired baud rate using the USART_BRR register.
 *
 * 6.  Set the TE bit in USART_CR1 to send an idle frame as first transmission.
 *
 * 7.  Write the data to send in the USART_DR register (this clears the TXE
 *     bit). Repeat this for each data to be transmitted in case of single buffer.
 *
 * 8.  After writing the last data into the USART_DR register, wait until TC=1.
 *     This indicates that the transmission of the last frame is complete. This is
 *     required for instance when the USART is disabled or enters the Halt mode to
 *     avoid corrupting the last transmission.
 *
 * Single byte communication
 * Clearing the TXE bit is always performed by a write to the data register.
 *
 * The TXE bit is set by hardware and it indicates:
 * ?   The data has been moved from TDR to the shift register and the data transmission has
 *     started.
 * ?   The TDR register is empty.
 * ?   The next data can be written in the USART_DR register without overwriting the
 *     previous data.
 * This flag generates an interrupt if the TXEIE bit is set.
 *
 * When a transmission is taking place, a write instruction to the USART_DR
 * register stores the data in the TDR register and which is copied in the
 * shift register at the end of the current transmission.
 *
 * When no transmission is taking place, a write instruction to the USART_DR
 * register places the data directly in the shift register, the data
 * transmission starts, and the TXE bit is immediately set.
 *
 * If a frame is transmitted (after the stop bit) and the TXE bit is set, the
 * TC bit goes high. An interrupt is generated if the TCIE bit is set in the
 * USART_CR1 register.  After writing the last data into the USART_DR register,
 * it is mandatory to wait for TC=1 before disabling the USART or causing the
 * microcontroller to enter the low power mode (see Figure 241: TC/TXE behavior
 * when transmitting).
 *
 * Clearing the TC bit is performed by the following software sequence:
 * 1.     A read from the USART_SR register
 * 2.     A write to the USART_DR register
 *
 *
 * For now, use 8N1
 *
 * Baud rate is generated by programming the mantissa and fraction values of
 * USARTDIV
 *
 * baud = fck / 16*USARTDIV
 * Fck = PLK1 for USART2 and USART3 = 36MHz
 * Fck = PCLK2 for USART1 = 72MHz
 *
 * Baud    Actual  USARTDIV_36MHZ  Error     USARTDIV_72MHZ Error
 * 2400    2.400   937.5           0%        1875           0%
 * 9600    9.600   234.375         0%        468.75         0%
 * 19200   19.2    117.1875        0%        234.375        0%
 * 57600   57.6    39.0625         0%        78.125         0.%
 * 115200  115.384 19.5            0.15%     39.0625        0%
 * 230400  230.769 9.75            0.16%     19.5           0.16%
 * 460800  461.538 4.875           0.16%     9.75           0.16%
 * 921600  923.076 2.4375          0.16%     4.875          0.16%
 * 225000  2250    1               0%        2              0%
 *
 * USART_BRR[15:4] = mantissa
 * USART_BRR[3:0] = fraction
 * 111010
 * 0110
 * */
#define NR_USARTS           0x3

//#define USART1_BASE         0x40013800
//#define USART2_BASE         0x40004400
//#define USART3_BASE         0x40004800

#define USART_UE            BIT(13)
#define USART_M             BIT(12)
#define USART_TE            BIT(3)
#define USART_TXE           BIT(7)
#define USART_STOP_BITS_1   BIT_MASK_SHIFT(0b0, 12)
#define USART_STOP_BITS_05  BIT_MASK_SHIFT(0b01, 12)
#define USART_STOP_BITS_2   BIT_MASK_SHIFT(0b02, 12)
#define USART_STOP_BITS_15  BIT_MASK_SHIFT(0b02, 12)

#define USART1_CLK          72000000UL
#define USART2_CLK          36000000UL
#define USART3_CLK          36000000UL

#define B9600_MANTISSA      0xEA
#define B9600_FRACTION      0x06


typedef struct usart_port {
    volatile uint32_t SR;
    volatile uint32_t DR;
    volatile uint32_t BRR;
    volatile uint32_t CR1;
    volatile uint32_t CR2;
    volatile uint32_t CR3;
    volatile uint32_t GTPR;
} usart_port;

#ifdef __cplusplus
extern "C"{
#endif

int32_t usart_init(uint8_t);


#ifdef __cplusplus
} // extern "C"
#endif


#endif