irq map
drivers/irqchip/irq-bcm2835.c
divided into 3 banks.
0-31 bank 0 => Basic Interrupt enable register. offset 0x218, bit 0-7
32-63 bank 1 => Interrupt enable register 1. offset 0x210, bit 0-31
64-95 bank 2 => Interrupt enable register 2. offset 0x214, bit 0-31
bank 1 and bank 2 are GPU interrupt.
the system timer compare interrupt 0-3 => bank 1, 0-3 => hw irq num is 32-35
compare 0, 2 used by gpu.
compare 1, 3 can be used by ARM.
UART idle状态下保持高电平，传输数据时，先下降为低电平，为start bit，在传输数据。传输结束后，在保持高电平，为stop bit。
一个bit传输的时间为1s/buard rate。例如波特率为9600，那么bit传输时间为1000000/9600=104us
一帧的传输时间为：(1+8+1)*104=1.04ms。
实现思路是，使用起始位的下降沿作为中断触发源。然后关闭该中断，使用定时器作为中断触发源，在每个传输位的中点时间触发中断，读取GPIO电平，一个帧完毕后，在开启GPIO中断。
因此用到了两个中断：RX GPIO中断，System Timer中断。前者用来表示新数据开始接收。后者用来接收每个位。
具体代码实现如下：
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See the * GNU General Public License for more details. * */#include <linux/module.h>#include <linux/gpio.h>#include <linux/interrupt.h>#include <linux/delay.h>#include <linux/kfifo.h>#include <linux/wait.h>#include <linux/cdev.h>#define DEBUG_SU 1#define SYS_TIMER_REG_BASE 0x3f003000#define SYS_TIMER_IRQNUM_BASE 32#define SOFT_UART_FIFO 32 #define SOFTUART_PORT_NR 1 enum { SU_RX_STATE_SYNC = 0, SU_RX_STATE_IDLE, SU_RX_STATE_START, SU_RX_STATE_DATA0, SU_RX_STATE_PARITY = SU_RX_STATE_DATA0 + 32, SU_RX_STATE_STOP,};/* See BCM2835-ARM-Peripherals.pdf Chapter 12 System Timer */struct system_timer{ uint32_t contrl_status; uint32_t count_low32; uint32_t count_high32; uint32_t compare[4];};struct soft_uart_port{ dev_t dev; struct cdev cdev; spinlock_t lock; wait_queue_head_t waitqueue; int line; unsigned long flags; int systimer; /* 0,2 is used by GPU, 1 for port 0, 3 for port 1 */ int rx_gpio; int tx_gpio; unsigned int buard_rate; int start_bits; int data_bits; int parity_bits; int stop_bits; unsigned int bit_time; unsigned int half_bit_time; int rx_irq_num; int tx_irq_num; char rx_label[32]; int rx_state; int sync_bits; int rx_intr_disabled; unsigned int rx_char; unsigned int rx_ts; DECLARE_KFIFO(rxfifo,unsigned char,SOFT_UART_FIFO); DECLARE_KFIFO(txfifo,unsigned char,SOFT_UART_FIFO); #if DEBUG_SU int rx_isr_in_irq; int rx_isr_num; unsigned int rx_isr_ts[128]; int timer_isr_num; unsigned int timer_isr_state[128]; unsigned int timer_isr_cmp[128]; unsigned int timer_isr_ts[128]; unsigned int timer_isr_end_ts[128]; int tempdata_len; int tempdata[128];#endif};struct soft_uart_driver{ volatile struct system_timer *sys_timer_regs; struct soft_uart_port port[SOFTUART_PORT_NR];};#define SOFTUART_DRIVER(p) container_of(p-p->line,struct soft_uart_driver,port[0])#if DEBUG_SUvoid dump_port_rx(struct soft_uart_port *port){ int i; printk("rx state %d\n", port->rx_state); printk("rx isr %d, timer isr %d\n", port->rx_isr_num, port->timer_isr_num); for (i = port->rx_isr_num - 1; port->rx_isr_num - i <= ARRAY_SIZE(port->rx_isr_ts) && i >= 0; i--) printk("rx isr %u\n", port->rx_isr_ts[i%ARRAY_SIZE(port->rx_isr_ts)]); for (i = port->timer_isr_num -1; port->timer_isr_num - i <= ARRAY_SIZE(port->timer_isr_ts) && i >= 0; i--) printk("idx %d, timer isr %u end %u cmp %u state %d\n", i, port->timer_isr_ts[i%ARRAY_SIZE(port->timer_isr_ts)], port->timer_isr_end_ts[i%ARRAY_SIZE(port->timer_isr_end_ts)], port->timer_isr_cmp[i%ARRAY_SIZE(port->timer_isr_cmp)], port->timer_isr_state[i%ARRAY_SIZE(port->timer_isr_state)]);}void dump_port_rx_data(struct soft_uart_port *port){ char buf[128]; int buflen = 0; int i; memset(buf, 0, sizeof(buf)); port->tempdata[port->tempdata_len++] = port->rx_char; if (port->tempdata_len >= 9) { for (i = 0; i < 9; i++) buflen += snprintf(buf+buflen, 127-buflen, "%02x", port->tempdata[i]); printk("%s\n", buf); port->tempdata_len = 0; }}#endifstatic inline void disable_rx_intr(struct soft_uart_port *port, int nosync){ if (!port->rx_intr_disabled) { port->rx_intr_disabled = 1; /* using in_irq() may walk into dead lock gpio isr may run at thread */ if (nosync) disable_irq_nosync(port->rx_irq_num); else disable_irq(port->rx_irq_num); }}static inline void enable_rx_intr(struct soft_uart_port *port) { if (port->rx_intr_disabled) { port->rx_intr_disabled = 0; enable_irq(port->rx_irq_num); }}static inline void trigger_timer(struct soft_uart_port *port, unsigned int ts){ struct soft_uart_driver *driver = SOFTUART_DRIVER(port); int systimer = port->systimer; driver->sys_timer_regs->compare[systimer] = ts;#if DEBUG_SU if (port->rx_state != SU_RX_STATE_SYNC) { unsigned int margin = ts - driver->sys_timer_regs->count_low32; port->timer_isr_cmp[port->timer_isr_num%ARRAY_SIZE(port->timer_isr_cmp)] = ts; if (margin < 16 || margin > 10000) printk("timer err trigger %u now %u\n", ts, driver->sys_timer_regs->count_low32); }#endif}static inline void clear_timer(struct soft_uart_port *port){ struct soft_uart_driver *driver = SOFTUART_DRIVER(port); int systimer = port->systimer; driver->sys_timer_regs->contrl_status = (1 << systimer);}static inline uint32_t timer_ts(struct soft_uart_port *port){ struct soft_uart_driver *driver = SOFTUART_DRIVER(port); return driver->sys_timer_regs->count_low32;}static inline int get_rx_value(struct soft_uart_port *port){ return !!gpio_get_value(port->rx_gpio);}static irqreturn_t st_isr(int irqnum, void *data){ unsigned long flags; struct soft_uart_port *port = (struct soft_uart_port *)data; int value = get_rx_value(port); #if DEBUG_SU int idx = -1;#endif spin_lock_irqsave(&port->lock, flags); clear_timer(port);#if DEBUG_SU if (port->rx_state != SU_RX_STATE_SYNC) { idx = (port->timer_isr_num++)%ARRAY_SIZE(port->timer_isr_ts); port->timer_isr_ts[idx] = timer_ts(port); port->timer_isr_state[idx] = port->rx_state; }#endif if (port->rx_state == SU_RX_STATE_SYNC) { if (value) { port->sync_bits++; if (port->sync_bits > 4 * 16) {#if DEBUG_SU printk("sync done\n");#endif port->rx_state = SU_RX_STATE_IDLE; enable_rx_intr(port); } else trigger_timer(port, timer_ts(port) + port->bit_time / 4); } else port->sync_bits = 0; } else if (port->rx_state == SU_RX_STATE_START) { if (value) { /* unstable interrupt triggered by gpio so we reenter IDLE state */ port->rx_state = SU_RX_STATE_IDLE; enable_rx_intr(port); } else { trigger_timer(port, port->rx_ts + port->half_bit_time + 1*port->bit_time); port->rx_state = SU_RX_STATE_DATA0; port->rx_char = 0; } } else if (port->rx_state >= SU_RX_STATE_DATA0 && port->rx_state < SU_RX_STATE_PARITY) { port->rx_char |= (value << (port->rx_state - SU_RX_STATE_DATA0)); port->rx_state++; trigger_timer(port, port->rx_ts + port->half_bit_time + (1+port->rx_state-SU_RX_STATE_DATA0)*port->bit_time); if (port->rx_state >= SU_RX_STATE_DATA0 + port->data_bits) { port->rx_state = SU_RX_STATE_STOP; } } else if (port->rx_state == SU_RX_STATE_STOP) { if (value) { kfifo_put(&port->rxfifo, (unsigned char)port->rx_char); wake_up_interruptible(&port->waitqueue);#if DEBUG_SU dump_port_rx_data(port);#endif } else { printk("ts %u\n", timer_ts(port) - port->rx_ts); printk("low stop bit\n"); } port->rx_state = SU_RX_STATE_IDLE; enable_rx_intr(port); }#if DEBUG_SU if (idx != -1) port->timer_isr_end_ts[idx] = timer_ts(port);#endif spin_unlock_irqrestore(&port->lock, flags); return IRQ_HANDLED;}static irqreturn_t softuart_rx_isr(int irqnum, void *data){ unsigned long flags; struct soft_uart_port *port = (struct soft_uart_port *)data; spin_lock_irqsave(&port->lock, flags); if (port->rx_state == SU_RX_STATE_SYNC) { spin_unlock_irqrestore(&port->lock, flags); return IRQ_HANDLED; }#if DEBUG_SU port->rx_isr_ts[(port->rx_isr_num++)%ARRAY_SIZE(port->rx_isr_ts)] = timer_ts(port); port->rx_isr_in_irq = in_irq(); if (port->rx_state != SU_RX_STATE_IDLE) { printk("invalid state %d\n", port->rx_state); }#endif disable_rx_intr(port, 1); port->rx_ts = timer_ts(port); port->rx_state = SU_RX_STATE_START; trigger_timer(port, port->rx_ts + port->half_bit_time); spin_unlock_irqrestore(&port->lock, flags); return IRQ_HANDLED;}static int softuart_rx_gpio_init(struct soft_uart_port *port){ int ret; int gpionum = port->rx_gpio; int irqnum; sprintf(port->rx_label, "softuart_rx%d\n", gpionum); ret = gpio_request(gpionum, port->rx_label); if (ret) { printk(KERN_ERR "request gpio failed: %d\n", ret); return ret; } ret = gpio_direction_input(gpionum); if (ret) { printk(KERN_ERR "set gpio to input failed: %d\n", ret); gpio_free(gpionum); return ret; } ret = gpio_to_irq(gpionum); if (ret < 0) { printk(KERN_ERR "gpio to irq failed: %d\n", ret); gpio_free(gpionum); return ret; } irqnum = ret; printk("gpio %d to irq %d\n", gpionum, irqnum); ret = request_irq(irqnum, softuart_rx_isr, IRQF_TRIGGER_FALLING, port->rx_label, port); if (ret) { printk(KERN_ERR "request irq failed\n"); return ret; } port->rx_irq_num = irqnum; return 0;}static void softuart_rx_gpio_free(struct soft_uart_port *port){ printk("free state %d\n", port->rx_state); if (!free_irq(port->rx_irq_num, port)) { printk(KERN_ERR "free irq failed\n"); } gpio_free(port->rx_gpio);}static int softuart_startup(struct soft_uart_port *port){ int ret; port->bit_time = 1000000 / port->buard_rate; port->half_bit_time = 500000 / port->buard_rate; port->rx_state = SU_RX_STATE_SYNC; port->rx_intr_disabled = 0; smp_wmb(); ret = request_irq(SYS_TIMER_IRQNUM_BASE+port->systimer, st_isr, 0, "system timer", port); if (ret < 0) { printk("request sys timer irq failed\n"); return ret; } ret = softuart_rx_gpio_init(port); if (ret) { printk(KERN_ERR "softuart_rx_init failed\n"); return ret; } /* disable rx interrupt and trigger sys timer to synchronize to idle state */ disable_rx_intr(port, 0); trigger_timer(port, timer_ts(port)+10); return 0;}static void softuart_shutdown(struct soft_uart_port *port){ free_irq(SYS_TIMER_IRQNUM_BASE+port->systimer, port); softuart_rx_gpio_free(port);}/********************** char device ***************************/ssize_t softuart_read(struct file *fp, char __user *data, size_t len, loff_t *off){ struct soft_uart_port *port = fp->private_data; int ret; int copied; ret = wait_event_interruptible(port->waitqueue, !kfifo_is_empty(&port->rxfifo)); if (ret == -ERESTARTSYS) { return -EINTR; } ret = kfifo_to_user(&port->rxfifo,data,len,&copied); if (ret) return ret; return copied;}ssize_t softuart_write (struct file *fp, const char __user *data, size_t len, loff_t *off){ printk("softuart write\n"); return 0;}int softuart_open(struct inode *inode, struct file *fp){ int ret; struct cdev *cdev = inode->i_cdev; struct soft_uart_port *port = container_of(cdev,struct soft_uart_port,cdev); fp->private_data = port; ret = softuart_startup(port); if (ret < 0) { printk("softuart_startup failed\n"); return ret; } printk("softuart open ok\n"); return 0;}int softuart_release(struct inode *inode, struct file *fp){ struct cdev *cdev = inode->i_cdev; struct soft_uart_port *port = container_of(cdev,struct soft_uart_port,cdev); softuart_shutdown(port); printk("softuart release\n"); return 0;}struct file_operations softuart_fops = { .owner = THIS_MODULE, .read = softuart_read, .write = softuart_write, .open = softuart_open, .release = softuart_release,};static struct soft_uart_driver softuart_driver = { .port = { { .line = 0, .systimer = 1, } }};static int buard_rate = 9600;static int rx_gpio = 21;static int tx_gpio = 20;static int start_bits = 1;static int data_bits = 8;static int parity_bits = 0;static int stop_bits = 1;static int __init mod_init(void){ int err; dev_t *dev; struct cdev *cdev; struct soft_uart_port *port; softuart_driver.sys_timer_regs = ioremap(SYS_TIMER_REG_BASE, sizeof(struct system_timer)); port = &softuart_driver.port[0]; port->buard_rate = buard_rate; port->rx_gpio = rx_gpio; port->tx_gpio = tx_gpio; port->start_bits = start_bits; port->data_bits = data_bits; port->parity_bits = parity_bits; port->stop_bits = stop_bits; spin_lock_init(&port->lock); INIT_KFIFO(port->rxfifo); INIT_KFIFO(port->txfifo); init_waitqueue_head(&port->waitqueue); dev = &softuart_driver.port[0].dev; cdev = &softuart_driver.port[0].cdev; err = alloc_chrdev_region(dev, 0, 1, "softuart"); if (err < 0) { printk(KERN_WARNING "alloc_chrdev_region() failed\n"); return err; } cdev_init(cdev, &softuart_fops); cdev->owner = THIS_MODULE; err = cdev_add(cdev, *dev, 1); if (err < 0){ printk(KERN_WARNING "cdev_add() failed\n"); unregister_chrdev_region(*dev, 1); return err; } return 0;}static void __exit mod_exit(void){ dev_t *dev = &softuart_driver.port[0].dev; struct cdev *cdev = &softuart_driver.port[0].cdev; unregister_chrdev_region(*dev, 1); cdev_del(cdev); iounmap(softuart_driver.sys_timer_regs);}module_init(mod_init);module_exit(mod_exit);MODULE_LICENSE("GPL");MODULE_AUTHOR("Yuan Jianpeng"); |
使用char device作为读取数据，没有使用UART层，主要是不熟悉UART层的接口。目前只实现了RX。TX相对更简单一点。
注意：中断必须在一个bit的时间内及时处理，否则数据将丢失。目前测试，主要是printk会关中断比较长的时间，导致问题。
References
http://xinu-os.org/BCM2835_Interrupt_Controller
http://xinu-os.org/BCM2835_System_Timer
Adrienne Prahler Jaffe. Implementation of a Software UART on TMS320C54x Using General-Purpose I/O Pins.