Cortex A: fix extra memory read and non-word sizes
Without this patch, to perform a memory read, OpenOCD first issues an LDC instruction into DBGITR in Stall mode (thus executing the instruction), then switches to Fast mode and reads from DBGDTRTX once for each word to transfer. At the very end of the transfer, the final Fast mode read of DBGDTRTX has, as always, the side effect of re-issuing the LDC instruction. This causes two problems: (1) If the word immediately beyond the end of the requested region is inaccessible, this spurious LDC will cause a fault. On a fast CPU, the LDC will finish executing by the time the poll of DSCR takes place, failing the entire memory read. On a slow CPU, the LDC might finish executing later, leaving an unexpected and confusing sticky fault lying around for the next operation to see. (2) If the LDC succeeds, it will leave the loaded word in DBGDTRTX, thus setting DBGDSCR.TXFULL=1. The cortex_a_read_apb_ab_memory routine completes without consuming that last word, thus confusing the next routine that tries to use DBGDTRTX (this may not have any visible effect on some implementations, because writing to DBGDTRTXint when TXFULL=1 is defined as Unpredictable, but I believe it caused a visible problem for me). With this patch, the bulk mem_ap_sel_read_buf_noincr is modified to omit the last word of the block. The second-to-last read of DBGDTRTX by that function will cause the issue of the LDC for the last word. After switching back to Normal mode and waiting for that instruction to finish, do a final read of DBGDTRTX to extract the last word into the buffer, leaving TXFULL=0. Without this patch, memory accesses are always expanded such that they are aligned to the access size. With this patch, accesses are issued exactly as ordered by the caller. The caller is expected to handle fragments at the beginning and end of the transfer if the address is unaligned and an unaligned access is not desired. Without this patch, the DFAR and DFSR registers, which report the location and status of data faults, are ignored while performing memory accesses, which could cause problems debugging an OS page fault handler. With this patch, DFAR and DFSR are preserved across memory accesses, and DFSR is decoded in the event of a synchronous fault to provide the caller with more information about the reason for failure. Thanks to Boris Brezillon for the original patch whose ideas led to the non-word access mechanism implemented here and to various code reviewers for their comments. Change-Id: I11ae7104fbe69a522efadefc705c9a217a7eef41 Signed-off-by: Christopher Head <chead@zaber.com> Reviewed-on: http://openocd.zylin.com/2381 Tested-by: jenkins Reviewed-by: Olivier Schonken <olivier.schonken@gmail.com> Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
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Christopher Head
Paul Fertser
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