Calibration of HAL_CounterDelay
-------------------------------

System under test:
  Acorn Risc PC motherboard serial number EMM-1000668
  Acorn StrongARM 233 rev S card serial number 05493139
  RISC OS 4.02
  HAL26 version 0.02
  
Test equipment:
  BlackStar model 1325 1300MHz frequency counter, serial number 66229
  calibrated 5 November 2002
  
Date of test: 25 January 2003

Measured crystal frequencies:
  Motherboard X1 nominal 64MHz: 64.005MHz
  SA card PLL crystal nominal 3.579545MHz:  3.579384MHz

The program Calibrate was used to test the HAL_CounterDelay function of HAL26
by toggling the D0 line on the parallel port, one toggle per delay.  A
constant error each cycle is introduced due to the delay of the parallel port
I/O - parallel_delay_calibrate suggests this is 1.006us per cycle.

The frequency counter was used to measure the period of pulses on D0 - this
was divided by 2 to determine the speed of toggling.

The results can be seen in the file Data/tsv.  The columns from left to right
are:

The delay parameter supplied to HAL_CounterDelay
The square wave period on D0 as measure by the frequency counter
The real delay measured - ie half the square wave period
This delay minus the parallel port access time
The error in us between requested delay and actual delay
This error as a percentage of the requested delay

