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/* $Id: dma.h,v 1.1 2005-12-20 11:35:33 jcastillo Exp $
 * linux/include/asm/dma.h: Defines for using and allocating dma channels.
 * Written by Hennus Bergman, 1992.
 * High DMA channel support & info by Hannu Savolainen
 * and John Boyd, Nov. 1992.
 */
 
#ifndef _ASM_DMA_H
#define _ASM_DMA_H
 
#include <asm/io.h>             /* need byte IO */
 
 
#ifdef HAVE_REALLY_SLOW_DMA_CONTROLLER
#define dma_outb        outb_p
#else
#define dma_outb        outb
#endif
 
#define dma_inb         inb
 
/*
 * NOTES about DMA transfers:
 *
 *  controller 1: channels 0-3, byte operations, ports 00-1F
 *  controller 2: channels 4-7, word operations, ports C0-DF
 *
 *  - ALL registers are 8 bits only, regardless of transfer size
 *  - channel 4 is not used - cascades 1 into 2.
 *  - channels 0-3 are byte - addresses/counts are for physical bytes
 *  - channels 5-7 are word - addresses/counts are for physical words
 *  - transfers must not cross physical 64K (0-3) or 128K (5-7) boundaries
 *  - transfer count loaded to registers is 1 less than actual count
 *  - controller 2 offsets are all even (2x offsets for controller 1)
 *  - page registers for 5-7 don't use data bit 0, represent 128K pages
 *  - page registers for 0-3 use bit 0, represent 64K pages
 *
 * DMA transfers are limited to the lower 16MB of _physical_ memory.
 * Note that addresses loaded into registers must be _physical_ addresses,
 * not logical addresses (which may differ if paging is active).
 *
 *  Address mapping for channels 0-3:
 *
 *   A23 ... A16 A15 ... A8  A7 ... A0    (Physical addresses)
 *    |  ...  |   |  ... |   |  ... |
 *    |  ...  |   |  ... |   |  ... |
 *    |  ...  |   |  ... |   |  ... |
 *   P7  ...  P0  A7 ... A0  A7 ... A0
 * |    Page    | Addr MSB | Addr LSB |   (DMA registers)
 *
 *  Address mapping for channels 5-7:
 *
 *   A23 ... A17 A16 A15 ... A9 A8 A7 ... A1 A0    (Physical addresses)
 *    |  ...  |   \   \   ... \  \  \  ... \  \
 *    |  ...  |    \   \   ... \  \  \  ... \  (not used)
 *    |  ...  |     \   \   ... \  \  \  ... \
 *   P7  ...  P1 (0) A7 A6  ... A0 A7 A6 ... A0
 * |      Page      |  Addr MSB   |  Addr LSB  |   (DMA registers)
 *
 * Again, channels 5-7 transfer _physical_ words (16 bits), so addresses
 * and counts _must_ be word-aligned (the lowest address bit is _ignored_ at
 * the hardware level, so odd-byte transfers aren't possible).
 *
 * Transfer count (_not # bytes_) is limited to 64K, represented as actual
 * count - 1 : 64K => 0xFFFF, 1 => 0x0000.  Thus, count is always 1 or more,
 * and up to 128K bytes may be transferred on channels 5-7 in one operation.
 *
 */
 
#define MAX_DMA_CHANNELS        8
 
/* The maximum address that we can perform a DMA transfer to on this platform */
#define MAX_DMA_ADDRESS      0x1000000
 
/* 8237 DMA controllers */
#define IO_DMA1_BASE    0x00    /* 8 bit slave DMA, channels 0..3 */
#define IO_DMA2_BASE    0xC0    /* 16 bit master DMA, ch 4(=slave input)..7 */
 
/* DMA controller registers */
#define DMA1_CMD_REG            0x08    /* command register (w) */
#define DMA1_STAT_REG           0x08    /* status register (r) */
#define DMA1_REQ_REG            0x09    /* request register (w) */
#define DMA1_MASK_REG           0x0A    /* single-channel mask (w) */
#define DMA1_MODE_REG           0x0B    /* mode register (w) */
#define DMA1_CLEAR_FF_REG       0x0C    /* clear pointer flip-flop (w) */
#define DMA1_TEMP_REG           0x0D    /* Temporary Register (r) */
#define DMA1_RESET_REG          0x0D    /* Master Clear (w) */
#define DMA1_CLR_MASK_REG       0x0E    /* Clear Mask */
#define DMA1_MASK_ALL_REG       0x0F    /* all-channels mask (w) */
 
#define DMA2_CMD_REG            0xD0    /* command register (w) */
#define DMA2_STAT_REG           0xD0    /* status register (r) */
#define DMA2_REQ_REG            0xD2    /* request register (w) */
#define DMA2_MASK_REG           0xD4    /* single-channel mask (w) */
#define DMA2_MODE_REG           0xD6    /* mode register (w) */
#define DMA2_CLEAR_FF_REG       0xD8    /* clear pointer flip-flop (w) */
#define DMA2_TEMP_REG           0xDA    /* Temporary Register (r) */
#define DMA2_RESET_REG          0xDA    /* Master Clear (w) */
#define DMA2_CLR_MASK_REG       0xDC    /* Clear Mask */
#define DMA2_MASK_ALL_REG       0xDE    /* all-channels mask (w) */
 
#define DMA_ADDR_0              0x00    /* DMA address registers */
#define DMA_ADDR_1              0x02
#define DMA_ADDR_2              0x04
#define DMA_ADDR_3              0x06
#define DMA_ADDR_4              0xC0
#define DMA_ADDR_5              0xC4
#define DMA_ADDR_6              0xC8
#define DMA_ADDR_7              0xCC
 
#define DMA_CNT_0               0x01    /* DMA count registers */
#define DMA_CNT_1               0x03
#define DMA_CNT_2               0x05
#define DMA_CNT_3               0x07
#define DMA_CNT_4               0xC2
#define DMA_CNT_5               0xC6
#define DMA_CNT_6               0xCA
#define DMA_CNT_7               0xCE
 
#define DMA_PAGE_0              0x87    /* DMA page registers */
#define DMA_PAGE_1              0x83
#define DMA_PAGE_2              0x81
#define DMA_PAGE_3              0x82
#define DMA_PAGE_5              0x8B
#define DMA_PAGE_6              0x89
#define DMA_PAGE_7              0x8A
 
#define DMA_MODE_READ   0x44    /* I/O to memory, no autoinit, increment, single mode */
#define DMA_MODE_WRITE  0x48    /* memory to I/O, no autoinit, increment, single mode */
#define DMA_MODE_CASCADE 0xC0   /* pass thru DREQ->HRQ, DACK<-HLDA only */
 
/* enable/disable a specific DMA channel */
static __inline__ void enable_dma(unsigned int dmanr)
{
        if (dmanr<=3)
                dma_outb(dmanr,  DMA1_MASK_REG);
        else
                dma_outb(dmanr & 3,  DMA2_MASK_REG);
}
 
static __inline__ void disable_dma(unsigned int dmanr)
{
        if (dmanr<=3)
                dma_outb(dmanr | 4,  DMA1_MASK_REG);
        else
                dma_outb((dmanr & 3) | 4,  DMA2_MASK_REG);
}
 
/* Clear the 'DMA Pointer Flip Flop'.
 * Write 0 for LSB/MSB, 1 for MSB/LSB access.
 * Use this once to initialize the FF to a known state.
 * After that, keep track of it. :-)
 * --- In order to do that, the DMA routines below should ---
 * --- only be used while interrupts are disabled! ---
 */
static __inline__ void clear_dma_ff(unsigned int dmanr)
{
        if (dmanr<=3)
                dma_outb(0,  DMA1_CLEAR_FF_REG);
        else
                dma_outb(0,  DMA2_CLEAR_FF_REG);
}
 
/* set mode (above) for a specific DMA channel */
static __inline__ void set_dma_mode(unsigned int dmanr, char mode)
{
        if (dmanr<=3)
                dma_outb(mode | dmanr,  DMA1_MODE_REG);
        else
                dma_outb(mode | (dmanr&3),  DMA2_MODE_REG);
}
 
/* Set only the page register bits of the transfer address.
 * This is used for successive transfers when we know the contents of
 * the lower 16 bits of the DMA current address register, but a 64k boundary
 * may have been crossed.
 */
static __inline__ void set_dma_page(unsigned int dmanr, char pagenr)
{
        switch(dmanr) {
                case 0:
                        dma_outb(pagenr, DMA_PAGE_0);
                        break;
                case 1:
                        dma_outb(pagenr, DMA_PAGE_1);
                        break;
                case 2:
                        dma_outb(pagenr, DMA_PAGE_2);
                        break;
                case 3:
                        dma_outb(pagenr, DMA_PAGE_3);
                        break;
                case 5:
                        dma_outb(pagenr & 0xfe, DMA_PAGE_5);
                        break;
                case 6:
                        dma_outb(pagenr & 0xfe, DMA_PAGE_6);
                        break;
                case 7:
                        dma_outb(pagenr & 0xfe, DMA_PAGE_7);
                        break;
        }
}
 
 
/* Set transfer address & page bits for specific DMA channel.
 * Assumes dma flipflop is clear.
 */
static __inline__ void set_dma_addr(unsigned int dmanr, unsigned int a)
{
        set_dma_page(dmanr, a>>16);
        if (dmanr <= 3)  {
            dma_outb( a & 0xff, ((dmanr&3)<<1) + IO_DMA1_BASE );
            dma_outb( (a>>8) & 0xff, ((dmanr&3)<<1) + IO_DMA1_BASE );
        }  else  {
            dma_outb( (a>>1) & 0xff, ((dmanr&3)<<2) + IO_DMA2_BASE );
            dma_outb( (a>>9) & 0xff, ((dmanr&3)<<2) + IO_DMA2_BASE );
        }
}
 
 
/* Set transfer size (max 64k for DMA1..3, 128k for DMA5..7) for
 * a specific DMA channel.
 * You must ensure the parameters are valid.
 * NOTE: from a manual: "the number of transfers is one more
 * than the initial word count"! This is taken into account.
 * Assumes dma flip-flop is clear.
 * NOTE 2: "count" represents _bytes_ and must be even for channels 5-7.
 */
static __inline__ void set_dma_count(unsigned int dmanr, unsigned int count)
{
        count--;
        if (dmanr <= 3)  {
            dma_outb( count & 0xff, ((dmanr&3)<<1) + 1 + IO_DMA1_BASE );
            dma_outb( (count>>8) & 0xff, ((dmanr&3)<<1) + 1 + IO_DMA1_BASE );
        } else {
            dma_outb( (count>>1) & 0xff, ((dmanr&3)<<2) + 2 + IO_DMA2_BASE );
            dma_outb( (count>>9) & 0xff, ((dmanr&3)<<2) + 2 + IO_DMA2_BASE );
        }
}
 
 
/* Get DMA residue count. After a DMA transfer, this
 * should return zero. Reading this while a DMA transfer is
 * still in progress will return unpredictable results.
 * If called before the channel has been used, it may return 1.
 * Otherwise, it returns the number of _bytes_ left to transfer.
 *
 * Assumes DMA flip-flop is clear.
 */
static __inline__ int get_dma_residue(unsigned int dmanr)
{
        unsigned int io_port = (dmanr<=3)? ((dmanr&3)<<1) + 1 + IO_DMA1_BASE
                                         : ((dmanr&3)<<2) + 2 + IO_DMA2_BASE;
 
        /* using short to get 16-bit wrap around */
        unsigned short count;
 
        count = 1 + dma_inb(io_port);
        count += dma_inb(io_port) << 8;
 
        return (dmanr<=3)? count : (count<<1);
}
 
 
/* These are in kernel/dma.c: */
extern int request_dma(unsigned int dmanr, const char * device_id);     /* reserve a DMA channel */
extern void free_dma(unsigned int dmanr);       /* release it again */
 
 
#endif /* _ASM_DMA_H */

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[/] [or1k/] [trunk/] [rc203soc/] [sw/] [uClinux/] [include/] [asm-i386/] [dma.h] - Blame information for rev 1765

Line No.	Rev	Author	Line
1	1633	jcastillo	`/* $Id: dma.h,v 1.1 2005-12-20 11:35:33 jcastillo Exp $`
2			`* linux/include/asm/dma.h: Defines for using and allocating dma channels.`
3			`* Written by Hennus Bergman, 1992.`
4			`* High DMA channel support & info by Hannu Savolainen`
5			`* and John Boyd, Nov. 1992.`
6			`*/`
7
8			`#ifndef _ASM_DMA_H`
9			`#define _ASM_DMA_H`
10
11			`#include <asm/io.h> /* need byte IO */`
12
13
14			`#ifdef HAVE_REALLY_SLOW_DMA_CONTROLLER`
15			`#define dma_outb outb_p`
16			`#else`
17			`#define dma_outb outb`
18			`#endif`
19
20			`#define dma_inb inb`
21
22			`/*`
23			`* NOTES about DMA transfers:`
24			`*`
25			`* controller 1: channels 0-3, byte operations, ports 00-1F`
26			`* controller 2: channels 4-7, word operations, ports C0-DF`
27			`*`
28			`* - ALL registers are 8 bits only, regardless of transfer size`
29			`* - channel 4 is not used - cascades 1 into 2.`
30			`* - channels 0-3 are byte - addresses/counts are for physical bytes`
31			`* - channels 5-7 are word - addresses/counts are for physical words`
32			`* - transfers must not cross physical 64K (0-3) or 128K (5-7) boundaries`
33			`* - transfer count loaded to registers is 1 less than actual count`
34			`* - controller 2 offsets are all even (2x offsets for controller 1)`
35			`* - page registers for 5-7 don't use data bit 0, represent 128K pages`
36			`* - page registers for 0-3 use bit 0, represent 64K pages`
37			`*`
38			`* DMA transfers are limited to the lower 16MB of _physical_ memory.`
39			`* Note that addresses loaded into registers must be _physical_ addresses,`
40			`* not logical addresses (which may differ if paging is active).`
41			`*`
42			`* Address mapping for channels 0-3:`
43			`*`
44			`* A23 ... A16 A15 ... A8 A7 ... A0 (Physical addresses)`
45			`* \| ... \| \| ... \| \| ... \|`
46			`* \| ... \| \| ... \| \| ... \|`
47			`* \| ... \| \| ... \| \| ... \|`
48			`* P7 ... P0 A7 ... A0 A7 ... A0`
49			`* \| Page \| Addr MSB \| Addr LSB \| (DMA registers)`
50			`*`
51			`* Address mapping for channels 5-7:`
52			`*`
53			`* A23 ... A17 A16 A15 ... A9 A8 A7 ... A1 A0 (Physical addresses)`
54			`* \| ... \| \ \ ... \ \ \ ... \ \`
55			`* \| ... \| \ \ ... \ \ \ ... \ (not used)`
56			`* \| ... \| \ \ ... \ \ \ ... \`
57			`* P7 ... P1 (0) A7 A6 ... A0 A7 A6 ... A0`
58			`* \| Page \| Addr MSB \| Addr LSB \| (DMA registers)`
59			`*`
60			`* Again, channels 5-7 transfer _physical_ words (16 bits), so addresses`
61			`* and counts _must_ be word-aligned (the lowest address bit is _ignored_ at`
62			`* the hardware level, so odd-byte transfers aren't possible).`
63			`*`
64			`* Transfer count (_not # bytes_) is limited to 64K, represented as actual`
65			`* count - 1 : 64K => 0xFFFF, 1 => 0x0000. Thus, count is always 1 or more,`
66			`* and up to 128K bytes may be transferred on channels 5-7 in one operation.`
67			`*`
68			`*/`
69
70			`#define MAX_DMA_CHANNELS 8`
71
72			`/* The maximum address that we can perform a DMA transfer to on this platform */`
73			`#define MAX_DMA_ADDRESS 0x1000000`
74
75			`/* 8237 DMA controllers */`
76			`#define IO_DMA1_BASE 0x00 /* 8 bit slave DMA, channels 0..3 */`
77			`#define IO_DMA2_BASE 0xC0 /* 16 bit master DMA, ch 4(=slave input)..7 */`
78
79			`/* DMA controller registers */`
80			`#define DMA1_CMD_REG 0x08 /* command register (w) */`
81			`#define DMA1_STAT_REG 0x08 /* status register (r) */`
82			`#define DMA1_REQ_REG 0x09 /* request register (w) */`
83			`#define DMA1_MASK_REG 0x0A /* single-channel mask (w) */`
84			`#define DMA1_MODE_REG 0x0B /* mode register (w) */`
85			`#define DMA1_CLEAR_FF_REG 0x0C /* clear pointer flip-flop (w) */`
86			`#define DMA1_TEMP_REG 0x0D /* Temporary Register (r) */`
87			`#define DMA1_RESET_REG 0x0D /* Master Clear (w) */`
88			`#define DMA1_CLR_MASK_REG 0x0E /* Clear Mask */`
89			`#define DMA1_MASK_ALL_REG 0x0F /* all-channels mask (w) */`
90
91			`#define DMA2_CMD_REG 0xD0 /* command register (w) */`
92			`#define DMA2_STAT_REG 0xD0 /* status register (r) */`
93			`#define DMA2_REQ_REG 0xD2 /* request register (w) */`
94			`#define DMA2_MASK_REG 0xD4 /* single-channel mask (w) */`
95			`#define DMA2_MODE_REG 0xD6 /* mode register (w) */`
96			`#define DMA2_CLEAR_FF_REG 0xD8 /* clear pointer flip-flop (w) */`
97			`#define DMA2_TEMP_REG 0xDA /* Temporary Register (r) */`
98			`#define DMA2_RESET_REG 0xDA /* Master Clear (w) */`
99			`#define DMA2_CLR_MASK_REG 0xDC /* Clear Mask */`
100			`#define DMA2_MASK_ALL_REG 0xDE /* all-channels mask (w) */`
101
102			`#define DMA_ADDR_0 0x00 /* DMA address registers */`
103			`#define DMA_ADDR_1 0x02`
104			`#define DMA_ADDR_2 0x04`
105			`#define DMA_ADDR_3 0x06`
106			`#define DMA_ADDR_4 0xC0`
107			`#define DMA_ADDR_5 0xC4`
108			`#define DMA_ADDR_6 0xC8`
109			`#define DMA_ADDR_7 0xCC`
110
111			`#define DMA_CNT_0 0x01 /* DMA count registers */`
112			`#define DMA_CNT_1 0x03`
113			`#define DMA_CNT_2 0x05`
114			`#define DMA_CNT_3 0x07`
115			`#define DMA_CNT_4 0xC2`
116			`#define DMA_CNT_5 0xC6`
117			`#define DMA_CNT_6 0xCA`
118			`#define DMA_CNT_7 0xCE`
119
120			`#define DMA_PAGE_0 0x87 /* DMA page registers */`
121			`#define DMA_PAGE_1 0x83`
122			`#define DMA_PAGE_2 0x81`
123			`#define DMA_PAGE_3 0x82`
124			`#define DMA_PAGE_5 0x8B`
125			`#define DMA_PAGE_6 0x89`
126			`#define DMA_PAGE_7 0x8A`
127
128			`#define DMA_MODE_READ 0x44 /* I/O to memory, no autoinit, increment, single mode */`
129			`#define DMA_MODE_WRITE 0x48 /* memory to I/O, no autoinit, increment, single mode */`
130			`#define DMA_MODE_CASCADE 0xC0 /* pass thru DREQ->HRQ, DACK<-HLDA only */`
131
132			`/* enable/disable a specific DMA channel */`
133			`static __inline__ void enable_dma(unsigned int dmanr)`
134			`{`
135			`if (dmanr<=3)`
136			`dma_outb(dmanr, DMA1_MASK_REG);`
137			`else`
138			`dma_outb(dmanr & 3, DMA2_MASK_REG);`
139			`}`
140
141			`static __inline__ void disable_dma(unsigned int dmanr)`
142			`{`
143			`if (dmanr<=3)`
144			`dma_outb(dmanr \| 4, DMA1_MASK_REG);`
145			`else`
146			`dma_outb((dmanr & 3) \| 4, DMA2_MASK_REG);`
147			`}`
148
149			`/* Clear the 'DMA Pointer Flip Flop'.`
150			`* Write 0 for LSB/MSB, 1 for MSB/LSB access.`
151			`* Use this once to initialize the FF to a known state.`
152			`* After that, keep track of it. :-)`
153			`* --- In order to do that, the DMA routines below should ---`
154			`* --- only be used while interrupts are disabled! ---`
155			`*/`
156			`static __inline__ void clear_dma_ff(unsigned int dmanr)`
157			`{`
158			`if (dmanr<=3)`
159			`dma_outb(0, DMA1_CLEAR_FF_REG);`
160			`else`
161			`dma_outb(0, DMA2_CLEAR_FF_REG);`
162			`}`
163
164			`/* set mode (above) for a specific DMA channel */`
165			`static __inline__ void set_dma_mode(unsigned int dmanr, char mode)`
166			`{`
167			`if (dmanr<=3)`
168			`dma_outb(mode \| dmanr, DMA1_MODE_REG);`
169			`else`
170			`dma_outb(mode \| (dmanr&3), DMA2_MODE_REG);`
171			`}`
172
173			`/* Set only the page register bits of the transfer address.`
174			`* This is used for successive transfers when we know the contents of`
175			`* the lower 16 bits of the DMA current address register, but a 64k boundary`
176			`* may have been crossed.`
177			`*/`
178			`static __inline__ void set_dma_page(unsigned int dmanr, char pagenr)`
179			`{`
180			`switch(dmanr) {`
181			`case 0:`
182			`dma_outb(pagenr, DMA_PAGE_0);`
183			`break;`
184			`case 1:`
185			`dma_outb(pagenr, DMA_PAGE_1);`
186			`break;`
187			`case 2:`
188			`dma_outb(pagenr, DMA_PAGE_2);`
189			`break;`
190			`case 3:`
191			`dma_outb(pagenr, DMA_PAGE_3);`
192			`break;`
193			`case 5:`
194			`dma_outb(pagenr & 0xfe, DMA_PAGE_5);`
195			`break;`
196			`case 6:`
197			`dma_outb(pagenr & 0xfe, DMA_PAGE_6);`
198			`break;`
199			`case 7:`
200			`dma_outb(pagenr & 0xfe, DMA_PAGE_7);`
201			`break;`
202			`}`
203			`}`
204
205
206			`/* Set transfer address & page bits for specific DMA channel.`
207			`* Assumes dma flipflop is clear.`
208			`*/`
209			`static __inline__ void set_dma_addr(unsigned int dmanr, unsigned int a)`
210			`{`
211			`set_dma_page(dmanr, a>>16);`
212			`if (dmanr <= 3) {`
213			`dma_outb( a & 0xff, ((dmanr&3)<<1) + IO_DMA1_BASE );`
214			`dma_outb( (a>>8) & 0xff, ((dmanr&3)<<1) + IO_DMA1_BASE );`
215			`} else {`
216			`dma_outb( (a>>1) & 0xff, ((dmanr&3)<<2) + IO_DMA2_BASE );`
217			`dma_outb( (a>>9) & 0xff, ((dmanr&3)<<2) + IO_DMA2_BASE );`
218			`}`
219			`}`
220
221
222			`/* Set transfer size (max 64k for DMA1..3, 128k for DMA5..7) for`
223			`* a specific DMA channel.`
224			`* You must ensure the parameters are valid.`
225			`* NOTE: from a manual: "the number of transfers is one more`
226			`* than the initial word count"! This is taken into account.`
227			`* Assumes dma flip-flop is clear.`
228			`* NOTE 2: "count" represents _bytes_ and must be even for channels 5-7.`
229			`*/`
230			`static __inline__ void set_dma_count(unsigned int dmanr, unsigned int count)`
231			`{`
232			`count--;`
233			`if (dmanr <= 3) {`
234			`dma_outb( count & 0xff, ((dmanr&3)<<1) + 1 + IO_DMA1_BASE );`
235			`dma_outb( (count>>8) & 0xff, ((dmanr&3)<<1) + 1 + IO_DMA1_BASE );`
236			`} else {`
237			`dma_outb( (count>>1) & 0xff, ((dmanr&3)<<2) + 2 + IO_DMA2_BASE );`
238			`dma_outb( (count>>9) & 0xff, ((dmanr&3)<<2) + 2 + IO_DMA2_BASE );`
239			`}`
240			`}`
241
242
243			`/* Get DMA residue count. After a DMA transfer, this`
244			`* should return zero. Reading this while a DMA transfer is`
245			`* still in progress will return unpredictable results.`
246			`* If called before the channel has been used, it may return 1.`
247			`* Otherwise, it returns the number of _bytes_ left to transfer.`
248			`*`
249			`* Assumes DMA flip-flop is clear.`
250			`*/`
251			`static __inline__ int get_dma_residue(unsigned int dmanr)`
252			`{`
253			`unsigned int io_port = (dmanr<=3)? ((dmanr&3)<<1) + 1 + IO_DMA1_BASE`
254			`: ((dmanr&3)<<2) + 2 + IO_DMA2_BASE;`
255
256			`/* using short to get 16-bit wrap around */`
257			`unsigned short count;`
258
259			`count = 1 + dma_inb(io_port);`
260			`count += dma_inb(io_port) << 8;`
261
262			`return (dmanr<=3)? count : (count<<1);`
263			`}`
264
265
266			`/* These are in kernel/dma.c: */`
267			`extern int request_dma(unsigned int dmanr, const char * device_id); /* reserve a DMA channel */`
268			`extern void free_dma(unsigned int dmanr); /* release it again */`
269
270
271			`#endif /* _ASM_DMA_H */`