// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/*
Architecture:

We can initialize a SPI driver, but we don't talk to the SPI driver itself, we address a device. A device essentially
is a combination of SPI port and CS pin, plus some information about the specifics of communication to the device
(timing, command/address length etc)

The essence of the interface to a device is a set of queues; one per device. The idea is that to send something to a SPI
device, you allocate a transaction descriptor. It contains some information about the transfer like the lenghth, address,
command etc, plus pointers to transmit and receive buffer. The address of this block gets pushed into the transmit queue. 
The SPI driver does its magic, and sends and retrieves the data eventually. The data gets written to the receive buffers, 
if needed the transaction descriptor is modified to indicate returned parameters and the entire thing goes into the return
queue, where whatever software initiated the transaction can retrieve it.

The entire thing is run from the SPI interrupt handler. If SPI is done transmitting/receiving but nothing is in the queue, 
it will not clear the SPI interrupt but just disable it. This way, when a new thing is sent, pushing the packet into the send 
queue and re-enabling the interrupt will trigger the interrupt again, which can then take care of the sending.
*/



#include <string.h>
#include "driver/spi_master.h"
#include "soc/gpio_sig_map.h"
#include "soc/spi_reg.h"
#include "soc/dport_reg.h"
#include "soc/spi_struct.h"
#include "soc/rtc_cntl_reg.h"
#include "rom/ets_sys.h"
#include "esp_types.h"
#include "esp_attr.h"
#include "esp_intr.h"
#include "esp_intr_alloc.h"
#include "esp_log.h"
#include "esp_err.h"
#include "freertos/FreeRTOS.h"
#include "freertos/semphr.h"
#include "freertos/xtensa_api.h"
#include "freertos/task.h"
#include "freertos/ringbuf.h"
#include "soc/soc.h"
#include "soc/dport_reg.h"
#include "soc/uart_struct.h"
#include "rom/lldesc.h"
#include "driver/uart.h"
#include "driver/gpio.h"
#include "driver/periph_ctrl.h"
#include "esp_heap_alloc_caps.h"

typedef struct spi_device_t spi_device_t;

#define NO_CS 3     //Number of CS pins per SPI host

typedef struct {
    spi_device_t *device[NO_CS];
    intr_handle_t intr;
    spi_dev_t *hw;
    spi_transaction_t *cur_trans;
    int cur_cs;
    lldesc_t dmadesc_tx, dmadesc_rx;
    bool no_gpio_matrix;
} spi_host_t;

struct spi_device_t {
    QueueHandle_t trans_queue;
    QueueHandle_t ret_queue;
    spi_device_interface_config_t cfg;
    spi_host_t *host;
};

static spi_host_t *spihost[3];


static const char *SPI_TAG = "spi_master";
#define SPI_CHECK(a, str, ret_val) \
    if (!(a)) { \
        ESP_LOGE(SPI_TAG,"%s(%d): %s", __FUNCTION__, __LINE__, str); \
        return (ret_val); \
    }

/*
 Stores a bunch of per-spi-peripheral data.
*/
typedef struct {
    const uint8_t spiclk_out;       //GPIO mux output signals
    const uint8_t spid_out;
    const uint8_t spiq_out;
    const uint8_t spiwp_out;
    const uint8_t spihd_out;
    const uint8_t spid_in;          //GPIO mux input signals
    const uint8_t spiq_in;
    const uint8_t spiwp_in;
    const uint8_t spihd_in;
    const uint8_t spics_out[3];     // /CS GPIO output mux signals
    const uint8_t spiclk_native;    //IO pins of IO_MUX muxed signals
    const uint8_t spid_native;
    const uint8_t spiq_native;
    const uint8_t spiwp_native;
    const uint8_t spihd_native;
    const uint8_t spics0_native;
    const uint8_t irq;              //irq source for interrupt mux
    const uint8_t irq_dma;          //dma irq source for interrupt mux
    const periph_module_t module;   //peripheral module, for enabling clock etc
    spi_dev_t *hw;              //Pointer to the hardware registers
} spi_signal_conn_t;

/*
 Bunch of constants for every SPI peripheral: GPIO signals, irqs, hw addr of registers etc
*/
static const spi_signal_conn_t io_signal[3]={
    {
        .spiclk_out=SPICLK_OUT_IDX,
        .spid_out=SPID_OUT_IDX,
        .spiq_out=SPIQ_OUT_IDX,
        .spiwp_out=SPIWP_OUT_IDX,
        .spihd_out=SPIHD_OUT_IDX,
        .spid_in=SPID_IN_IDX,
        .spiq_in=SPIQ_IN_IDX,
        .spiwp_in=SPIWP_IN_IDX,
        .spihd_in=SPIHD_IN_IDX,
        .spics_out={SPICS0_OUT_IDX, SPICS1_OUT_IDX, SPICS2_OUT_IDX},
        .spiclk_native=6,
        .spid_native=8,
        .spiq_native=7,
        .spiwp_native=10,
        .spihd_native=9,
        .spics0_native=11,
        .irq=ETS_SPI1_INTR_SOURCE,
        .irq_dma=ETS_SPI1_DMA_INTR_SOURCE,
        .module=PERIPH_SPI_MODULE,
        .hw=&SPI1
    }, {
        .spiclk_out=HSPICLK_OUT_IDX,
        .spid_out=HSPID_OUT_IDX,
        .spiq_out=HSPIQ_OUT_IDX,
        .spiwp_out=HSPIWP_OUT_IDX,
        .spihd_out=HSPIHD_OUT_IDX,
        .spid_in=HSPID_IN_IDX,
        .spiq_in=HSPIQ_IN_IDX,
        .spiwp_in=HSPIWP_IN_IDX,
        .spihd_in=HSPIHD_IN_IDX,
        .spics_out={HSPICS0_OUT_IDX, HSPICS1_OUT_IDX, HSPICS2_OUT_IDX},
        .spiclk_native=14,
        .spid_native=13,
        .spiq_native=12,
        .spiwp_native=2,
        .spihd_native=4,
        .spics0_native=15,
        .irq=ETS_SPI2_INTR_SOURCE,
        .irq_dma=ETS_SPI2_DMA_INTR_SOURCE,
        .module=PERIPH_HSPI_MODULE,
        .hw=&SPI2
    }, {
        .spiclk_out=VSPICLK_OUT_IDX,
        .spid_out=VSPID_OUT_IDX,
        .spiq_out=VSPIQ_OUT_IDX,
        .spiwp_out=VSPIWP_OUT_IDX,
        .spihd_out=VSPIHD_OUT_IDX,
        .spid_in=VSPID_IN_IDX,
        .spiq_in=VSPIQ_IN_IDX,
        .spiwp_in=VSPIWP_IN_IDX,
        .spihd_in=VSPIHD_IN_IDX,
        .spics_out={VSPICS0_OUT_IDX, VSPICS1_OUT_IDX, VSPICS2_OUT_IDX},
        .spiclk_native=18,
        .spid_native=23,
        .spiq_native=19,
        .spiwp_native=22,
        .spihd_native=21,
        .spics0_native=5,
        .irq=ETS_SPI3_INTR_SOURCE,
        .irq_dma=ETS_SPI3_DMA_INTR_SOURCE,
        .module=PERIPH_VSPI_MODULE,
        .hw=&SPI3
    }
};

static void spi_intr(void *arg);


esp_err_t spi_bus_initialize(spi_host_device_t host, spi_bus_config_t *bus_config, int dma_chan)
{
    bool native=true;
    /* ToDo: remove this when we have flash operations cooperating with this */
    SPI_CHECK(host!=SPI_HOST, "SPI1 is not supported", ESP_ERR_NOT_SUPPORTED);

    SPI_CHECK(host>=SPI_HOST && host<=VSPI_HOST, "invalid host", ESP_ERR_INVALID_ARG);
    SPI_CHECK(spihost[host]==NULL, "host already in use", ESP_ERR_INVALID_STATE);
    
    SPI_CHECK(bus_config->mosi_io_num<0 || GPIO_IS_VALID_OUTPUT_GPIO(bus_config->mosi_io_num), "spid pin invalid", ESP_ERR_INVALID_ARG);
    SPI_CHECK(bus_config->sclk_io_num<0 || GPIO_IS_VALID_OUTPUT_GPIO(bus_config->sclk_io_num), "spiclk pin invalid", ESP_ERR_INVALID_ARG);
    SPI_CHECK(bus_config->miso_io_num<0 || GPIO_IS_VALID_GPIO(bus_config->miso_io_num), "spiq pin invalid", ESP_ERR_INVALID_ARG);
    SPI_CHECK(bus_config->quadwp_io_num<0 || GPIO_IS_VALID_OUTPUT_GPIO(bus_config->quadwp_io_num), "spiwp pin invalid", ESP_ERR_INVALID_ARG);
    SPI_CHECK(bus_config->quadhd_io_num<0 || GPIO_IS_VALID_OUTPUT_GPIO(bus_config->quadhd_io_num), "spihd pin invalid", ESP_ERR_INVALID_ARG);

    //The host struct contains two dma descriptors, so we need DMA'able memory for this.
    spihost[host]=pvPortMallocCaps(sizeof(spi_host_t), MALLOC_CAP_DMA);
    if (spihost[host]==NULL) return ESP_ERR_NO_MEM;
    memset(spihost[host], 0, sizeof(spi_host_t));
    
    //Check if the selected pins correspond to the native pins of the peripheral
    if (bus_config->mosi_io_num >= 0 && bus_config->mosi_io_num!=io_signal[host].spid_native) native=false;
    if (bus_config->miso_io_num >= 0 && bus_config->miso_io_num!=io_signal[host].spiq_native) native=false;
    if (bus_config->sclk_io_num >= 0 && bus_config->sclk_io_num!=io_signal[host].spiclk_native) native=false;
    if (bus_config->quadwp_io_num >= 0 && bus_config->quadwp_io_num!=io_signal[host].spiwp_native) native=false;
    if (bus_config->quadhd_io_num >= 0 && bus_config->quadhd_io_num!=io_signal[host].spihd_native) native=false;
    
    spihost[host]->no_gpio_matrix=native;
    if (native) {
        //All SPI native pin selections resolve to 1, so we put that here instead of trying to figure
        //out which FUNC_GPIOx_xSPIxx to grab; they all are defined to 1 anyway.
        if (bus_config->mosi_io_num > 0) PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->mosi_io_num], 1);
        if (bus_config->miso_io_num > 0) PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->miso_io_num], 1);
        if (bus_config->quadwp_io_num > 0) PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->quadwp_io_num], 1);
        if (bus_config->quadhd_io_num > 0) PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->quadhd_io_num], 1);
        if (bus_config->sclk_io_num > 0) PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->sclk_io_num], 1);
    } else {
        //Use GPIO 
        if (bus_config->mosi_io_num>0) {
            PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->mosi_io_num], PIN_FUNC_GPIO);
            gpio_set_direction(bus_config->mosi_io_num, GPIO_MODE_OUTPUT);
            gpio_matrix_out(bus_config->mosi_io_num, io_signal[host].spid_out, false, false);
            gpio_matrix_in(bus_config->mosi_io_num, io_signal[host].spid_in, false);
        }
        if (bus_config->miso_io_num>0) {
            PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->miso_io_num], PIN_FUNC_GPIO);
            gpio_set_direction(bus_config->miso_io_num, GPIO_MODE_INPUT);
            gpio_matrix_out(bus_config->miso_io_num, io_signal[host].spiq_out, false, false);
            gpio_matrix_in(bus_config->miso_io_num, io_signal[host].spiq_in, false);
        }
        if (bus_config->quadwp_io_num>0) {
            PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->quadwp_io_num], PIN_FUNC_GPIO);
            gpio_set_direction(bus_config->quadwp_io_num, GPIO_MODE_OUTPUT);
            gpio_matrix_out(bus_config->quadwp_io_num, io_signal[host].spiwp_out, false, false);
            gpio_matrix_in(bus_config->quadwp_io_num, io_signal[host].spiwp_in, false);
        }
        if (bus_config->quadhd_io_num>0) {
            PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->quadhd_io_num], PIN_FUNC_GPIO);
            gpio_set_direction(bus_config->quadhd_io_num, GPIO_MODE_OUTPUT);
            gpio_matrix_out(bus_config->quadhd_io_num, io_signal[host].spihd_out, false, false);
            gpio_matrix_in(bus_config->quadhd_io_num, io_signal[host].spihd_in, false);
        }
        if (bus_config->sclk_io_num>0) {
            PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[bus_config->sclk_io_num], PIN_FUNC_GPIO);
            gpio_set_direction(bus_config->sclk_io_num, GPIO_MODE_OUTPUT);
            gpio_matrix_out(bus_config->sclk_io_num, io_signal[host].spiclk_out, false, false);
        }
    }
    periph_module_enable(io_signal[host].module);
    esp_intr_alloc(io_signal[host].irq, ESP_INTR_FLAG_INTRDISABLED, spi_intr, (void*)spihost[host], &spihost[host]->intr);
    spihost[host]->hw=io_signal[host].hw;

    //Reset DMA
    spihost[host]->hw->dma_conf.val|=SPI_OUT_RST|SPI_AHBM_RST|SPI_AHBM_FIFO_RST;
    spihost[host]->hw->dma_out_link.start=0;
    spihost[host]->hw->dma_in_link.start=0;
    spihost[host]->hw->dma_conf.val&=~(SPI_OUT_RST|SPI_AHBM_RST|SPI_AHBM_FIFO_RST);
    //Reset timing
    spihost[host]->hw->ctrl2.val=0;

    //Disable unneeded ints
    spihost[host]->hw->slave.rd_buf_done=0;
    spihost[host]->hw->slave.wr_buf_done=0;
    spihost[host]->hw->slave.rd_sta_done=0;
    spihost[host]->hw->slave.wr_sta_done=0;
    spihost[host]->hw->slave.rd_buf_inten=0;
    spihost[host]->hw->slave.wr_buf_inten=0;
    spihost[host]->hw->slave.rd_sta_inten=0;
    spihost[host]->hw->slave.wr_sta_inten=0;

    //Force a transaction done interrupt. This interrupt won't fire yet because we initialized the SPI interrupt as
    //disabled.  This way, we can just enable the SPI interrupt and the interrupt handler will kick in, handling 
    //any transactions that are queued.
    spihost[host]->hw->slave.trans_inten=1;
    spihost[host]->hw->slave.trans_done=1;

    //Select DMA channel.
    SET_PERI_REG_BITS(DPORT_SPI_DMA_CHAN_SEL_REG, 3, dma_chan, (host * 2));

    return ESP_OK;
}

esp_err_t spi_bus_free(spi_host_device_t host)
{
    int x;
    SPI_CHECK(host>=SPI_HOST && host<=VSPI_HOST, "invalid host", ESP_ERR_INVALID_ARG);
    SPI_CHECK(spihost[host]!=NULL, "host not in use", ESP_ERR_INVALID_STATE);
    for (x=0; x<NO_CS; x++) {
        SPI_CHECK(spihost[host]->device[x]==NULL, "not all CSses freed", ESP_ERR_INVALID_STATE);
    }
    spihost[host]->hw->slave.trans_inten=0;
    spihost[host]->hw->slave.trans_done=0;
    esp_intr_free(spihost[host]->intr);
    periph_module_disable(io_signal[host].module);
    free(spihost[host]);
    spihost[host]=NULL;
    return ESP_OK;
}

/*
 Add a device. This allocates a CS line for the device, allocates memory for the device structure and hooks
 up the CS pin to whatever is specified.
*/
esp_err_t spi_bus_add_device(spi_host_device_t host, spi_device_interface_config_t *dev_config, spi_device_handle_t *handle)
{
    int freecs;
    int apbclk=APB_CLK_FREQ;
    SPI_CHECK(host>=SPI_HOST && host<=VSPI_HOST, "invalid host", ESP_ERR_INVALID_ARG);
    SPI_CHECK(spihost[host]!=NULL, "host not initialized", ESP_ERR_INVALID_STATE);
    SPI_CHECK(dev_config->spics_io_num < 0 || GPIO_IS_VALID_OUTPUT_GPIO(dev_config->spics_io_num), "spics pin invalid", ESP_ERR_INVALID_ARG);
    SPI_CHECK(dev_config->clock_speed_hz > 0, "invalid sclk speed", ESP_ERR_INVALID_ARG);
    for (freecs=0; freecs<NO_CS; freecs++) {
        //See if this slot is free; reserve if it is by putting a dummy pointer in the slot. We use an atomic compare&swap to make this thread-safe.
        if (__sync_bool_compare_and_swap(&spihost[host]->device[freecs], NULL, (spi_device_t *)1)) break;
    }
    SPI_CHECK(freecs!=NO_CS, "no free cs pins for host", ESP_ERR_NOT_FOUND);
    //The hardware looks like it would support this, but actually setting cs_ena_pretrans when transferring in full
    //duplex mode does absolutely nothing on the ESP32.
    SPI_CHECK(dev_config->cs_ena_pretrans==0 || (dev_config->flags & SPI_DEVICE_HALFDUPLEX), "cs pretrans delay incompatible with full-duplex", ESP_ERR_INVALID_ARG);
    //Speeds >=40MHz over GPIO matrix needs a dummy cycle, but these don't work for full-duplex connections.
    SPI_CHECK(!( ((dev_config->flags & SPI_DEVICE_HALFDUPLEX)==0) && (dev_config->clock_speed_hz > ((apbclk*2)/5)) && (!spihost[host]->no_gpio_matrix)),
            "No speeds >26MHz supported for full-duplex, GPIO-matrix SPI transfers", ESP_ERR_INVALID_ARG);

    //Allocate memory for device
    spi_device_t *dev=malloc(sizeof(spi_device_t));
    if (dev==NULL) return ESP_ERR_NO_MEM;
    memset(dev, 0, sizeof(spi_device_t));
    spihost[host]->device[freecs]=dev;

    //Allocate queues, set defaults
    dev->trans_queue=xQueueCreate(dev_config->queue_size, sizeof(spi_transaction_t *));
    dev->ret_queue=xQueueCreate(dev_config->queue_size, sizeof(spi_transaction_t *));
    if (dev_config->duty_cycle_pos==0) dev_config->duty_cycle_pos=128;
    dev->host=spihost[host];

    //We want to save a copy of the dev config in the dev struct.
    memcpy(&dev->cfg, dev_config, sizeof(spi_device_interface_config_t));

    //Set CS pin, CS options
    if (dev_config->spics_io_num > 0) {
        if (spihost[host]->no_gpio_matrix &&dev_config->spics_io_num == io_signal[host].spics0_native && freecs==0) {
            //Again, the cs0s for all SPI peripherals map to pin mux source 1, so we use that instead of a define.
            PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[dev_config->spics_io_num], 1);
        } else {
            //Use GPIO matrix
            PIN_FUNC_SELECT(GPIO_PIN_MUX_REG[dev_config->spics_io_num], PIN_FUNC_GPIO);
            gpio_set_direction(dev_config->spics_io_num, GPIO_MODE_OUTPUT);
            gpio_matrix_out(dev_config->spics_io_num, io_signal[host].spics_out[freecs], false, false);
        }
    }
    if (dev_config->flags&SPI_DEVICE_CLK_AS_CS) {
        spihost[host]->hw->pin.master_ck_sel |= (1<<freecs);
    } else {
        spihost[host]->hw->pin.master_ck_sel &= (1<<freecs);
    }
    if (dev_config->flags&SPI_DEVICE_POSITIVE_CS) {
        spihost[host]->hw->pin.master_cs_pol |= (1<<freecs);
    } else {
        spihost[host]->hw->pin.master_cs_pol &= (1<<freecs);
    }
    *handle=dev;
    return ESP_OK;
}

esp_err_t spi_bus_remove_device(spi_device_handle_t handle)
{
    int x;
    SPI_CHECK(handle!=NULL, "invalid handle", ESP_ERR_INVALID_ARG);
    //These checks aren't exhaustive; another thread could sneak in a transaction inbetween. These are only here to
    //catch design errors and aren't meant to be triggered during normal operation.
    SPI_CHECK(uxQueueMessagesWaiting(handle->trans_queue)==0, "Have unfinished transactions", ESP_ERR_INVALID_STATE);
    SPI_CHECK(handle->host->cur_trans==0 || handle->host->device[handle->host->cur_cs]!=handle, "Have unfinished transactions", ESP_ERR_INVALID_STATE);
    SPI_CHECK(uxQueueMessagesWaiting(handle->ret_queue)==0, "Have unfinished transactions", ESP_ERR_INVALID_STATE);

    //Kill queues
    vQueueDelete(handle->trans_queue);
    vQueueDelete(handle->ret_queue);
    //Remove device from list of csses and free memory
    for (x=0; x<NO_CS; x++) {
        if (handle->host->device[x] == handle) handle->host->device[x]=NULL;
    }
    free(handle);
    return ESP_OK;
}

static int spi_freq_for_pre_n(int fapb, int pre, int n) {
    return (fapb / (pre * n));
}

/*
 * Set the SPI clock to a certain frequency. Returns the effective frequency set, which may be slightly
 * different from the requested frequency.
 */
static int spi_set_clock(spi_dev_t *hw, int fapb, int hz, int duty_cycle) {
    int pre, n, h, l, eff_clk;

    //In hw, n, h and l are 1-64, pre is 1-8K. Value written to register is one lower than used value.
    if (hz>((fapb/4)*3)) {
        //Using Fapb directly will give us the best result here.
        hw->clock.clkcnt_l=0;
        hw->clock.clkcnt_h=0;
        hw->clock.clkcnt_n=0;
        hw->clock.clkdiv_pre=0;
        hw->clock.clk_equ_sysclk=1;
        eff_clk=fapb;
    } else {
        //For best duty cycle resolution, we want n to be as close to 32 as possible, but
        //we also need a pre/n combo that gets us as close as possible to the intended freq.
        //To do this, we bruteforce n and calculate the best pre to go along with that.
        //If there's a choice between pre/n combos that give the same result, use the one
        //with the higher n.
        int bestn=-1;
        int bestpre=-1;
        int besterr=0;
        int errval;
        for (n=1; n<=64; n++) {
            //Effectively, this does pre=round((fapb/n)/hz).
            pre=((fapb/n)+(hz/2))/hz;
            if (pre<=0) pre=1;
            if (pre>8192) pre=8192;
            errval=abs(spi_freq_for_pre_n(fapb, pre, n)-hz);
            if (bestn==-1 || errval<=besterr) {
                besterr=errval;
                bestn=n;
                bestpre=pre;
            }
        }

        n=bestn;
        pre=bestpre;
        l=n;
        //This effectively does round((duty_cycle*n)/256)
        h=(duty_cycle*n+127)/256;
        if (h<=0) h=1;

        hw->clock.clk_equ_sysclk=0;
        hw->clock.clkcnt_n=n-1;
        hw->clock.clkdiv_pre=pre-1;
        hw->clock.clkcnt_h=h-1;
        hw->clock.clkcnt_l=l-1;
        eff_clk=spi_freq_for_pre_n(fapb, pre, n);
    }
    return eff_clk;
}


//If a transaction is smaller than or equal to of bits, we do not use DMA; instead, we directly copy/paste
//bits from/to the work registers. Keep between 32 and (8*32) please.
#define THRESH_DMA_TRANS (8*32)

//This is run in interrupt context and apart from initialization and destruction, this is the only code
//touching the host (=spihost[x]) variable. The rest of the data arrives in queues. That is why there are
//no muxes in this code.
static void IRAM_ATTR spi_intr(void *arg)
{
    int i;
    int prevCs=-1;
    BaseType_t r;
    BaseType_t do_yield=pdFALSE;
    spi_transaction_t *trans=NULL;
    spi_host_t *host=(spi_host_t*)arg;

    //Ignore all but the trans_done int.
    if (!host->hw->slave.trans_done) return;

    if (host->cur_trans) {
        //Okay, transaction is done. 
        if ((host->cur_trans->rx_buffer || (host->cur_trans->flags & SPI_TRANS_USE_RXDATA)) && host->cur_trans->rxlength<=THRESH_DMA_TRANS) {
            //Need to copy from SPI regs to result buffer.
            uint32_t *data;
            if (host->cur_trans->flags & SPI_TRANS_USE_RXDATA) {
                data=(uint32_t*)&host->cur_trans->rx_data[0];
            } else {
                data=(uint32_t*)host->cur_trans->rx_buffer;
            }
            for (int x=0; x < host->cur_trans->rxlength; x+=32) {
                //Do a memcpy to get around possible alignment issues in rx_buffer
                uint32_t word=host->hw->data_buf[x/32];
                memcpy(&data[x/32], &word, 4);
            }
        }
        //Call post-transaction callback, if any
        if (host->device[host->cur_cs]->cfg.post_cb) host->device[host->cur_cs]->cfg.post_cb(host->cur_trans);
        //Return transaction descriptor.
        xQueueSendFromISR(host->device[host->cur_cs]->ret_queue, &host->cur_trans, &do_yield);
        host->cur_trans=NULL;
        prevCs=host->cur_cs;
    }
    //ToDo: This is a stupidly simple low-cs-first priority scheme. Make this configurable somehow. - JD
    for (i=0; i<NO_CS; i++) {
        if (host->device[i]) {
            r=xQueueReceiveFromISR(host->device[i]->trans_queue, &trans, &do_yield);
            //Stop looking if we have a transaction to send.
            if (r) break;
        }
    }
    if (i==NO_CS) {
        //No packet waiting. Disable interrupt.
        esp_intr_disable(host->intr);
    } else {
        host->hw->slave.trans_done=0; //clear int bit
        //We have a transaction. Send it.
        spi_device_t *dev=host->device[i];
        host->cur_trans=trans;
        host->cur_cs=i;
        //We should be done with the transmission.
        assert(host->hw->cmd.usr == 0);
        
        //Default rxlength to be the same as length, if not filled in.
        if (trans->rxlength==0) {
            trans->rxlength=trans->length;
        }
        
        //Reconfigure according to device settings, but only if we change CSses.
        if (i!=prevCs) {
            //Assumes a hardcoded 80MHz Fapb for now. ToDo: figure out something better once we have
            //clock scaling working.
            int apbclk=APB_CLK_FREQ;
            int effclk=spi_set_clock(host->hw, apbclk, dev->cfg.clock_speed_hz, dev->cfg.duty_cycle_pos);
            //Configure bit order
            host->hw->ctrl.rd_bit_order=(dev->cfg.flags & SPI_DEVICE_RXBIT_LSBFIRST)?1:0;
            host->hw->ctrl.wr_bit_order=(dev->cfg.flags & SPI_DEVICE_TXBIT_LSBFIRST)?1:0;
            
            //Configure polarity
            //SPI iface needs to be configured for a delay in some cases.
            int nodelay=0;
            int extra_dummy=0;
            if (host->no_gpio_matrix) {
                if (effclk >= apbclk/2) {
                    nodelay=1;
                }
            } else {
                if (effclk >= apbclk/2) {
                    nodelay=1;
                    extra_dummy=1;          //Note: This only works on half-duplex connections. spi_bus_add_device checks for this.
                } else if (effclk >= apbclk/4) {
                    nodelay=1;
                }
            }

            if (dev->cfg.mode==0) {
                host->hw->pin.ck_idle_edge=0;
                host->hw->user.ck_out_edge=0;
                host->hw->ctrl2.miso_delay_mode=nodelay?0:2;
            } else if (dev->cfg.mode==1) {
                host->hw->pin.ck_idle_edge=0;
                host->hw->user.ck_out_edge=1;
                host->hw->ctrl2.miso_delay_mode=nodelay?0:1;
            } else if (dev->cfg.mode==2) {
                host->hw->pin.ck_idle_edge=1;
                host->hw->user.ck_out_edge=1;
                host->hw->ctrl2.miso_delay_mode=nodelay?0:1;
            } else if (dev->cfg.mode==3) {
                host->hw->pin.ck_idle_edge=1;
                host->hw->user.ck_out_edge=0;
                host->hw->ctrl2.miso_delay_mode=nodelay?0:2;
            }

            //Configure bit sizes, load addr and command
            host->hw->user.usr_dummy=(dev->cfg.dummy_bits+extra_dummy)?1:0;
            host->hw->user.usr_addr=(dev->cfg.address_bits)?1:0;
            host->hw->user.usr_command=(dev->cfg.command_bits)?1:0;
            host->hw->user1.usr_addr_bitlen=dev->cfg.address_bits-1;
            host->hw->user1.usr_dummy_cyclelen=dev->cfg.dummy_bits+extra_dummy-1;
            host->hw->user2.usr_command_bitlen=dev->cfg.command_bits-1;
            //Configure misc stuff
            host->hw->user.doutdin=(dev->cfg.flags & SPI_DEVICE_HALFDUPLEX)?0:1;
            host->hw->user.sio=(dev->cfg.flags & SPI_DEVICE_3WIRE)?1:0;

            host->hw->ctrl2.setup_time=dev->cfg.cs_ena_pretrans-1;
            host->hw->user.cs_setup=dev->cfg.cs_ena_pretrans?1:0;
            host->hw->ctrl2.hold_time=dev->cfg.cs_ena_posttrans-1;
            host->hw->user.cs_hold=(dev->cfg.cs_ena_posttrans)?1:0;

            //Configure CS pin
            host->hw->pin.cs0_dis=(i==0)?0:1;
            host->hw->pin.cs1_dis=(i==1)?0:1;
            host->hw->pin.cs2_dis=(i==2)?0:1;
        }
        //Reset DMA
        host->hw->dma_conf.val |= SPI_OUT_RST|SPI_AHBM_RST|SPI_AHBM_FIFO_RST;
        host->hw->dma_out_link.start=0;
        host->hw->dma_in_link.start=0;
        host->hw->dma_conf.val &= ~(SPI_OUT_RST|SPI_AHBM_RST|SPI_AHBM_FIFO_RST);
        //QIO/DIO
        host->hw->ctrl.val &= ~(SPI_FREAD_DUAL|SPI_FREAD_QUAD|SPI_FREAD_DIO|SPI_FREAD_QIO);
        host->hw->user.val &= ~(SPI_FWRITE_DUAL|SPI_FWRITE_QUAD|SPI_FWRITE_DIO|SPI_FWRITE_QIO);
        if (trans->flags & SPI_TRANS_MODE_DIO) {
            if (trans->flags & SPI_TRANS_MODE_DIOQIO_ADDR) {
                host->hw->ctrl.fread_dio=1;
                host->hw->user.fwrite_dio=1;
            } else {
                host->hw->ctrl.fread_dual=1;
                host->hw->user.fwrite_dual=1;
            }
            host->hw->ctrl.fastrd_mode=1;
        } else if (trans->flags & SPI_TRANS_MODE_QIO) {
            if (trans->flags & SPI_TRANS_MODE_DIOQIO_ADDR) {
                host->hw->ctrl.fread_qio=1;
                host->hw->user.fwrite_qio=1;
            } else {
                host->hw->ctrl.fread_quad=1;
                host->hw->user.fwrite_quad=1;
            }
            host->hw->ctrl.fastrd_mode=1;
        }


        //Fill DMA descriptors
        if (trans->rx_buffer || (trans->flags & SPI_TRANS_USE_RXDATA)) {
            uint32_t *data;
            if (trans->flags & SPI_TRANS_USE_RXDATA) {
                data=(uint32_t *)&trans->rx_data[0];
            } else {
                data=trans->rx_buffer;
            }
            if (trans->rxlength <= THRESH_DMA_TRANS) {
                //No need for DMA; we'll copy the result out of the work registers directly later.
            } else {
                host->hw->user.usr_miso_highpart=0;
                host->dmadesc_rx.size=(trans->rxlength+7)/8;
                host->dmadesc_rx.length=(trans->rxlength+7)/8;
                host->dmadesc_rx.buf=(uint8_t*)data;
                host->dmadesc_rx.eof=1;
                host->dmadesc_rx.sosf=0;
                host->dmadesc_rx.owner=1;
                host->hw->dma_in_link.addr=(int)(&host->dmadesc_rx)&0xFFFFF;
                host->hw->dma_in_link.start=1;
            }
            host->hw->user.usr_miso=1;
        } else {
            host->hw->user.usr_miso=0;
        }

        if (trans->tx_buffer || (trans->flags & SPI_TRANS_USE_TXDATA)) {
            uint32_t *data;
            if (trans->flags & SPI_TRANS_USE_TXDATA) {
                data=(uint32_t *)&trans->tx_data[0];
            } else {
                data=(uint32_t *)trans->tx_buffer;
            }
            if (trans->length <= THRESH_DMA_TRANS) {
                //No need for DMA.
                for (int x=0; x < trans->length; x+=32) {
                    //Use memcpy to get around alignment issues for txdata
                    uint32_t word;
                    memcpy(&word, &data[x/32], 4);
                    host->hw->data_buf[(x/32)+8]=word;
                }
                host->hw->user.usr_mosi_highpart=1;
            } else {
                host->hw->user.usr_mosi_highpart=0;
                host->dmadesc_tx.size=(trans->length+7)/8;
                host->dmadesc_tx.length=(trans->length+7)/8;
                host->dmadesc_tx.buf=(uint8_t*)data;
                host->dmadesc_tx.eof=1;
                host->dmadesc_tx.sosf=0;
                host->dmadesc_tx.owner=1;
                host->hw->dma_out_link.addr=(int)(&host->dmadesc_tx) & 0xFFFFF;
                host->hw->dma_out_link.start=1;
            }
        }
        host->hw->mosi_dlen.usr_mosi_dbitlen=trans->length-1;
        host->hw->miso_dlen.usr_miso_dbitlen=trans->rxlength-1;
        host->hw->user2.usr_command_value=trans->command;
        if (dev->cfg.address_bits>32) {
            host->hw->addr=trans->address >> 32;
            host->hw->slv_wr_status=trans->address & 0xffffffff;
        } else {
            host->hw->addr=trans->address & 0xffffffff;
        }
        host->hw->user.usr_mosi=(trans->tx_buffer==NULL)?0:1;
        host->hw->user.usr_miso=(trans->rx_buffer==NULL)?0:1;

        //Call pre-transmission callback, if any
        if (dev->cfg.pre_cb) dev->cfg.pre_cb(trans);
        //Kick off transfer
        host->hw->cmd.usr=1;
    }
    if (do_yield) portYIELD_FROM_ISR();
}


esp_err_t spi_device_queue_trans(spi_device_handle_t handle, spi_transaction_t *trans_desc,  TickType_t ticks_to_wait)
{
    BaseType_t r;
    SPI_CHECK(handle!=NULL, "invalid dev handle", ESP_ERR_INVALID_ARG);
    SPI_CHECK((trans_desc->flags & SPI_TRANS_USE_RXDATA)==0 ||trans_desc->length <= 32, "rxdata transfer > 32bytes", ESP_ERR_INVALID_ARG);
    SPI_CHECK((trans_desc->flags & SPI_TRANS_USE_TXDATA)==0 ||trans_desc->length <= 32, "txdata transfer > 32bytes", ESP_ERR_INVALID_ARG);
    SPI_CHECK(!((trans_desc->flags & (SPI_TRANS_MODE_DIO|SPI_TRANS_MODE_QIO)) && (handle->cfg.flags & SPI_DEVICE_3WIRE)), "incompatible iface params", ESP_ERR_INVALID_ARG);
    SPI_CHECK(!((trans_desc->flags & (SPI_TRANS_MODE_DIO|SPI_TRANS_MODE_QIO)) && (!(handle->cfg.flags & SPI_DEVICE_HALFDUPLEX))), "incompatible iface params", ESP_ERR_INVALID_ARG);
    r=xQueueSend(handle->trans_queue, (void*)&trans_desc, ticks_to_wait);
    if (!r) return ESP_ERR_TIMEOUT;
    esp_intr_enable(handle->host->intr);
    return ESP_OK;
}

esp_err_t spi_device_get_trans_result(spi_device_handle_t handle, spi_transaction_t **trans_desc, TickType_t ticks_to_wait)
{
    BaseType_t r;
    SPI_CHECK(handle!=NULL, "invalid dev handle", ESP_ERR_INVALID_ARG);
    r=xQueueReceive(handle->ret_queue, (void*)trans_desc, ticks_to_wait);
    if (!r) return ESP_ERR_TIMEOUT;
    return ESP_OK;
}

//Porcelain to do one blocking transmission.
esp_err_t spi_device_transmit(spi_device_handle_t handle, spi_transaction_t *trans_desc)
{
    esp_err_t ret;
    spi_transaction_t *ret_trans;
    //ToDo: check if any spi transfers in flight
    ret=spi_device_queue_trans(handle, trans_desc, portMAX_DELAY);
    if (ret!=ESP_OK) return ret;
    ret=spi_device_get_trans_result(handle, &ret_trans, portMAX_DELAY);
    if (ret!=ESP_OK) return ret;
    assert(ret_trans==trans_desc);
    return ESP_OK;
}

