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swd: Improve parity calculation and move it to types.h 

It could be reused by SWD drivers and in other places.

Change-Id: Ieed0cf70c111a73d3a42ed59f46a0cdd177a73d5
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1957
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>
__archive__
Andreas Fritiofson 2014-02-17 00:27:09 +01:00
parent 0e95ec4070
commit 36772a7ed0
2 changed files with 20 additions and 12 deletions
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19
src/helper/types.h
View File

@ -270,6 +270,25 @@ static inline void buf_bswap32(uint8_t *dst, const uint8_t *src, size_t len)
} }
} }
/**
* Calculate the (even) parity of a 32-bit datum.
* @param x The datum.
* @return 1 if the number of set bits in x is odd, 0 if it is even.
*/
static inline int parity_u32(uint32_t x)
{
#ifdef __GNUC__
return __builtin_parityl(x);
#else
x ^= x >> 16;
x ^= x >> 8;
x ^= x >> 4;
x ^= x >> 2;
x ^= x >> 1;
return x & 1;
#endif
}
#if defined(__ECOS) #if defined(__ECOS)
/* eCos plain lacks these definition... A series of upstream patches /* eCos plain lacks these definition... A series of upstream patches

13
src/jtag/swd.h
View File

@ -32,17 +32,6 @@
#define SWD_CMD_PARK (0 << 7) /* not driven by host (pull high) */ #define SWD_CMD_PARK (0 << 7) /* not driven by host (pull high) */
/* followed by TRN, 3-bits of ACK, TRN */ /* followed by TRN, 3-bits of ACK, TRN */
/* pbit16 holds precomputed parity bits for each nibble */
#define pbit(parity, nibble) ((parity) << (nibble))
static const uint16_t pbit16 =
pbit(0, 0) | pbit(1, 1) | pbit(1, 2) | pbit(0, 3)
| pbit(1, 4) | pbit(0, 5) | pbit(0, 6) | pbit(1, 7)
| pbit(1, 8) | pbit(0, 9) | pbit(0, 0xa) | pbit(1, 0xb)
| pbit(0, 0xc) | pbit(1, 0xd) | pbit(1, 0xe) | pbit(0, 0xf);
#define nibble_parity(nibble) (pbit16 & pbit(1, (nibble)))
/** /**
* Construct a "cmd" byte, in lSB bit order, which swd_driver.read_reg() * Construct a "cmd" byte, in lSB bit order, which swd_driver.read_reg()
* and swd_driver.write_reg() methods will use directly. * and swd_driver.write_reg() methods will use directly.
@ -54,7 +43,7 @@ static inline uint8_t swd_cmd(bool is_read, bool is_ap, uint8_t regnum)
| ((regnum & 0xc) << 1); | ((regnum & 0xc) << 1);
/* 8 cmd bits 4:1 may be set */ /* 8 cmd bits 4:1 may be set */
if (nibble_parity(cmd >> 1)) if (parity_u32(cmd))
cmd |= SWD_CMD_PARITY; cmd |= SWD_CMD_PARITY;
/* driver handles START, STOP, and TRN */ /* driver handles START, STOP, and TRN */