1 # $NetBSD: ncr5380.doc,v 1.5 2005/12/11 12:21:28 christos Exp $ 2 3 MI 5380 driver 4 ============== 5 6 (What? Documentation? Is this guy nuts? :-) 7 8 Reselection 9 ----------- 10 11 This driver will permit reselection on non-polled commands if 12 sc->sc_flags & NCR5380_PERMIT_RESELECT is 1. This permits enabling of 13 reselection on a per-device basis. 14 15 Disconnect/reselect is never permitted for polled commands. 16 17 18 19 Interfacing the driver to MD code 20 --------------------------------- 21 22 /sys/dev/ic/ncr5380.c is now stand-alone. DON'T include it after your 23 MD stuff! 24 25 This allows for more than one 5380-based SCSI board in your system. This is 26 a real possibility for Amiga generic kernels. 27 28 Your driver's softc structure must have an instance of struct ncr5380_softc 29 as the first thing in the structure. The MD code must initialize the 30 following: 31 32 sci_*: pointers to the 5380 registers. All accesses are done through 33 these pointers. This indirection allows the driver to work with 34 boards that map the 5380 on even addresses only or do other 35 weirdnesses. 36 37 int (*sc_pio_out)(sc, phase, datalen, data) 38 int (*sc_pio_in)(sc, phase, datalen, data) 39 These point to functions that do programmed I/O transfers to the bus and 40 from the bus, respectively. Arguments: 41 42 sc points to the softc 43 phase the current SCSI bus phase 44 datalen length of data to transfer 45 data pointer to the buffer 46 47 Both functions must return the number of bytes successfully transferred. 48 A transfer operation must be aborted if the target requests a different 49 phase before the transfer completes. 50 51 If you have no special requirements, you can point these to 52 ncr5380_pio_out() and ncr5380_pio_in() respectively. If your board 53 can do pseudo-DMA, then you might want to point these to functions 54 that use this feature. 55 56 void (*sc_dma_alloc)(sc) 57 This function is called to set up a DMA transfer. You must create and 58 return a "DMA handle" in sc->sc_dma_hand which identifies the DMA transfer. 59 The driver will pass you your DMA handle in sc->sc_dma_hand for future 60 operations. The contents of the DMA handle are immaterial to the MI 61 code - the DMA handle is for your bookkeeping only. Usually, you 62 create a structure and point to it here. 63 64 For example, you can record the mapped and unmapped addresses of the 65 buffer. The Sun driver places an Am9516 UDC control block in the DMA 66 handle. 67 68 If for some reason you decide not to do DMA for the transfer, make 69 sc->sc_dma_hand NULL. This might happen if the proposed transfer is 70 misaligned, or in the wrong type of memory, or... 71 72 void (*sc_dma_start)(sc) 73 This function starts the transfer. 74 75 void (*sc_dma_stop)(sc) 76 This function stops a transfer. sc->sc_datalen and sc->sc_dataptr must 77 be updated to reflect the portion of the DMA already done. 78 79 void (*sc_dma_eop)(sc) 80 This function is called when the 5380 signals EOP. Either continue 81 the DMA or stop the DMA. 82 83 void (*sc_dma_free)(sc) 84 This function frees the current DMA handle. 85 86 u_char *sc_dataptr; 87 int sc_datalen; 88 These variables form the active SCSI data pointer. DMA code must start 89 DMA at the location given, and update the pointer/length in response to 90 DMA operations. 91 92 u_short sc_dma_flags; 93 See ncr5380var.h 94 95 96 97 Writing your DMA code 98 --------------------- 99 100 DMA on a system with protected or virtual memory is always a problem. Even 101 though a disk transfer may be logically contiguous, the physical pages backing 102 the transfer may not be. There are two common solutions to this problem: 103 104 DMA chains: the DMA is broken up into a list of contiguous segments. The first 105 segment is submitted to the DMA controller, and when it completes, the second 106 segment is submitted, without stopping the 5380. This is what the sc_dma_eop() 107 function can do efficiently - if you have a DMA chain, it can quickly load up 108 the next link in the chain. The sc_dma_alloc() function builds the chain and 109 sc_dma_free() releases any resources you used to build it. 110 111 DVMA: Direct Virtual Memory Access. In this scheme, DMA requests go through 112 the MMU. Although you can't page fault, you can program the MMU to remap 113 things so the DMA controller sees contiguous data. In this mode, sc_dma_alloc() 114 is used to map the transfer into the address space reserved for DVMA and 115 sc_dma_free() is used to unmap it. 116 117 118 Interrupts 119 ---------- 120 121 ncr5380_sbc_intr() must be called when the 5380 interrupts the host. 122 123 You must write an interrupt routine pretty much from scratch to check for 124 things generated by MD hardware. 125 126 127 Known problems 128 -------------- 129 130 I'm getting this out now so that other ports can hack on it and integrate it. 131 132 The sun3, DMA/Interrupt appears to be working now, but needs testing. 133 134 Polled commands submitted while non-polled commands are in progress are not 135 handled correctly. This can happen if reselection is enabled and a new disk 136 is mounted while an I/O is in progress on another disk. 137 138 The problem is: what to do if you get reselected while doing the selection 139 for the polled command? Currently, the driver busy waits for the non-polled 140 command to complete, but this is bogus. I need to complete the non-polled 141 command in polled mode, then do the polled command. 142 143 144 Timeouts in the driver are EXTREMELY sensitive to the characteristics of the 145 local implementation of delay(). The Sun3 version delays for a minimum of 5us. 146 However, the driver must assume that delay(1) will delay only 1us. For this 147 reason, performance on the Sun3 sucks in some places. 148 149
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