+}
+
+int
+achi_alloc_slot(struct ahci_port* port)
+{
+ hba_reg_t pxsact = port->regs[HBA_RPxSACT];
+ hba_reg_t pxci = port->regs[HBA_RPxCI];
+ hba_reg_t free_bmp = pxsact | pxci;
+ uint32_t i = 0;
+ for (; i <= hba.cmd_slots && (free_bmp & 0x1); i++, free_bmp >>= 1)
+ ;
+ return i | -(i > hba.cmd_slots);
+}
+
+void
+__ahci_create_fis(struct sata_reg_fis* cmd_fis,
+ uint8_t command,
+ uint32_t lba_lo,
+ uint32_t lba_hi,
+ uint16_t sector_count)
+{
+ cmd_fis->head.type = SATA_REG_FIS_H2D;
+ cmd_fis->head.options = SATA_REG_FIS_COMMAND;
+ cmd_fis->head.status_cmd = command;
+ cmd_fis->dev = 0;
+
+ cmd_fis->lba0 = SATA_LBA_COMPONENT(lba_lo, 0);
+ cmd_fis->lba8 = SATA_LBA_COMPONENT(lba_lo, 8);
+ cmd_fis->lba16 = SATA_LBA_COMPONENT(lba_lo, 16);
+ cmd_fis->lba24 = SATA_LBA_COMPONENT(lba_lo, 24);
+
+ cmd_fis->lba32 = SATA_LBA_COMPONENT(lba_hi, 0);
+ cmd_fis->lba40 = SATA_LBA_COMPONENT(lba_hi, 8);
+
+ cmd_fis->count = sector_count;
+}
+
+int
+ahci_identify_device(struct ahci_port* port)
+{
+ int slot = achi_alloc_slot(port);
+ assert_msg(slot >= 0, "No free slot");
+
+ // 清空任何待响应的中断
+ port->regs[HBA_RPxIS] = 0;
+
+ /* 发送ATA命令，参考：SATA AHCI Spec Rev.1.3.1, section 5.5 */
+
+ // 构建命令头（Command Header）和命令表（Command Table）
+ struct ahci_hba_cmdh* cmd_header = &port->cmdlst[slot];
+ struct ahci_hba_cmdt* cmd_table = valloc_dma(sizeof(struct ahci_hba_cmdt));
+
+ memset(cmd_header, 0, sizeof(*cmd_header));
+ memset(cmd_table, 0, sizeof(*cmd_table));
+
+ // 预备DMA接收缓存，用于存放HBA传回的数据
+ uint16_t* data_in = (uint16_t*)valloc_dma(512);
+
+ cmd_table->entries[0] =
+ (struct ahci_hba_prdte){ .data_base = vmm_v2p(data_in),
+ .byte_count = 511 }; // byte_count是从0开始算的
+
+ // 在命令表中构建命令FIS
+ struct sata_reg_fis* cmd_fis = (struct sata_reg_fis*)cmd_table->command_fis;
+
+ // 根据设备类型使用合适的命令
+ if (port->regs[HBA_RPxSIG] == HBA_DEV_SIG_ATA) {
+ // ATA 一般为硬盘
+ __ahci_create_fis(cmd_fis, ATA_IDENTIFY_DEVICE, 0, 0, 0);
+ } else {
+ // ATAPI 一般为光驱，软驱，或者磁带机
+ __ahci_create_fis(cmd_fis, ATA_IDENTIFY_PAKCET_DEVICE, 0, 0, 0);
+ }
+
+ // 将命令表挂到命令头上
+ cmd_header->cmd_table_base = vmm_v2p(cmd_table);
+ cmd_header->prdt_len = 1;
+ cmd_header->options |=
+ HBA_CMDH_FIS_LEN(sizeof(*cmd_fis)) | HBA_CMDH_CLR_BUSY;
+
+ // PxCI寄存器置位，告诉HBA这儿有个数据需要发送到SATA端口
+ port->regs[HBA_RPxCI] = (1 << slot);
+
+ wait_until(!(port->regs[HBA_RPxCI] & (1 << slot)));
+
+ /*
+ 等待数据到达内存
+ 解析IDENTIFY DEVICE传回来的数据。
+ 参考：
+ * ATA/ATAPI Command Set - 3 (ACS-3), Section 7.12.7
+
+ 注意：ATAPI无法通过IDENTIFY PACKET DEVICE 获取容量信息。
+ 这需要另外使用特殊的SCSI命令中的READ CAPACITY(16)
+ 来获取，这种命令需要使用ATA的PACKET命令发出。
+ 参考：
+ * ATA/ATAPI Command Set - 3 (ACS-3), Section 7.18
+ * SATA AHCI HBA Spec, Section 5.3.7
+ * SCSI Command Reference Manual, Section 3.26
+ */
+ port->device_info = valloc(sizeof(struct ahci_device_info));
+ ahci_parse_dev_info(port->device_info, data_in);
+
+ vfree_dma(data_in);
+ vfree_dma(cmd_table);
+
+ return 1;
+}
+
+// TODO: Support ATAPI Device.
\ No newline at end of file
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